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The dispersal of pyroclasts from ancient explosive volcanoes on Mars: Implications for the friable layered deposits
Abstract
A number of voluminous, fine-grained, friable deposits have been mapped on Mars. The modes of origin for these deposits are debated. The feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit. It is concluded that the Medusae Fossae Formation and Electris deposits are easily formed through volcanic processes, and that the Hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes. The Arabia and Argyre deposits are not well replicated by modeled pyroclast dispersal, suggesting that these deposits were most likely emplaced by other means.
... The change from sulfates to rhythmites has been hypothesized to record global climate change [17]. Global mechanisms such as ashfall from large caldera-forming eruptions and climate-controlled dust circulation and induration have been proposed for rhythmite accumulation ( [18][19][20], but see also [2]). Here we test and reject these hypotheses using new datasets and for the first time synthesize the layer thickness, deposit thickness and volume, and age of Mars' young layered sedimentary rocks. ...
... Thus, accumulation in these different geographic areas was likely governed by regional depositional processes (Figs. 4, S3, S6, S11) (although in principle global dust storms could account for this type of variability with a single sediment source [21]). Valles Marineris sites show thinning away from the Tharsis volcanoes, as expected for a volcanic origin [18,19], although this trend is slight. Conversely, the Arabia and Medusae Fossae Formation sites lack clear intra-regional trends in latitude or distance from volcanic sources. ...
... The differences in trends and in fractional variance between deposits suggests that sediment deposition in these two regions was governed by independent regional controls/independent sediment sources. Globally we do not observe a trend of thicker layers at lower latitudes [20], nor thinning layers away from the major volcanic centers [18,19]. This is inconsistent with previously proposed simple models. ...
Mars' sedimentary rocks record Gyrs of environmental change. New data enable the first global analysis of paleo-environment relevant physical properties of these rocks, including layer thickness and accumulation rate. We find that layer thicknesses of post-3.5 Ga sedimentary rocks across the Martian surface show coherent variations at ~1000 km-scale that are inconsistent with simple volcanic and climatic hypotheses for formation, which are consistent with global compositional homogeneity at orbital scales. These data, in combination with new analyses of outcrop age and total rock volume demonstrate a global decrease in layer thickness that predates the eventual drop off in preserved sedimentary rock volume per Myr. The new constraints confirm a diachronous transition in Mars' global sedimentary rock record while also highlighting a regional dichotomy in young sedimentary rock deposits that has not been quantified before.
... Previous investigations into LLDs suggest a pyroclastic origin for the initial material accumulation and date it to the Late Hesperian (Le Deit et al., 2010;Weitz et al., 2008Weitz et al., , 2010. Studies modeling the distribution of ash fall from Ascraeus, Pavonis and Arsia Montes (∼2,000 km west of the region examined in this study) show that they could contribute significant pyroclastic material to the plains surrounding western VM (Hynek et al., 2003;Kerber et al., 2011Kerber et al., , 2012. Based on modeled ash dispersal patterns, Kerber et al. (2012) illustrate that the rim deposits being emplaced through pyroclastic volcanism is a viable hypothesis, and the most likely source of deposit material. ...
... Studies modeling the distribution of ash fall from Ascraeus, Pavonis and Arsia Montes (∼2,000 km west of the region examined in this study) show that they could contribute significant pyroclastic material to the plains surrounding western VM (Hynek et al., 2003;Kerber et al., 2011Kerber et al., , 2012. Based on modeled ash dispersal patterns, Kerber et al. (2012) illustrate that the rim deposits being emplaced through pyroclastic volcanism is a viable hypothesis, and the most likely source of deposit material. Modeling indicates that ashfall contributions to the regions where we have mapped rim deposits exceed a total thickness of 200 m, which is far thicker than observed; however, these models are contingent upon ...
... Recent research has proposed the existence of a volcanic edifice (provisionally labeled "Noctis Mons") situated within Noctis Labyrinthus (Figure 7) (Lee & Shubham, 2024). This putative volcano is at the correct latitude (exactly due west of the Ius Chasma) and is less than 500 km away from the nearest identified rim deposits, placing it over 1,100 km closer than the large volcanoes modeled by Kerber et al. (2012). Based on the inferred profile of Noctis Mons (Figure 7c), the caldera was ∼30 km in diameter prior to collapse, and the caldera depth, along with its prominence above the surrounding terrain is ∼3 km. ...
Layered deposits are found on the plateaus surrounding the western portion of Valles Marineris, mantling the chasmata rims. These rim deposits exhibit intricate layering and are described as light‐toned layered deposits (LLDs) in previous studies. Light‐toned layered deposits are thought to be composed of pyroclastic ash that was emplaced during volcanic eruptions and later chemically altered. Using Shallow Radar (SHARAD) observations to map radar reflections from what appears to be the base of these deposits, we discovered two additional types of rim deposits that are contiguous with the well‐known LLDs; weakly layered deposits (WLDs) that exhibit less obvious stratification and completely unstratified deposits designated as nonlayered deposits (NDs). Complementing the SHARAD data with imagery from Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) and with narrow‐angle imagery from the Mars Global Surveyor Mars Observer Camera (MOC‐NA), we mapped the full extent of all rim deposits and present the finished map within this study. We hypothesize that all three deposits originate from pyroclastic ashfall but experienced different degrees of modification due to the variable presence of liquid water. This hypothesis requires a source of volcanic depositional material and past aqueous environments in regions with LLDs and WLDs. We discuss the potential for several large Tharsis volcanoes and a hypothesized degraded volcano within Noctis Labyrinthus as sources of the ash, and we examine the evidence for past aqueous environments.
... The vast MFF, the westernmost extent of which maps to Zephyria Planum bedrock (Fig. 1C), is interpreted as a pyroclastic deposit on the basis of erosional morphology, draping of underlying topography, density, compositional information, and multiple radar data sets (Brož et al., 2021). Given the distribution of pyroclastic deposits on Mars (Kerber et al., 2012;Tanaka et al., 2014), the discovery of a pyroclastic source for the Zephyria Planum sand provides a mechanism for the wide-spread distribution of Martian sand from local sources. Explosive deposits with sand-sized grains are A B Fig. 1C), show that sand transport into Aeolis Dorsa is limited. ...
... widespread on Mars ( Wilson and Head, 1994;Kerber et al., 2012;Brož et al., 2021). Though fine sands will fall very close to the vent (Kerber et al., 2012), the potential for saltative sand transport at moderate wind speeds (Sullivan and Kok, 2017;Andreotti et al., 2021) allows for further distribution. ...
... widespread on Mars ( Wilson and Head, 1994;Kerber et al., 2012;Brož et al., 2021). Though fine sands will fall very close to the vent (Kerber et al., 2012), the potential for saltative sand transport at moderate wind speeds (Sullivan and Kok, 2017;Andreotti et al., 2021) allows for further distribution. Pyroclastic deposits have been inferred globally (Tanaka et al., 2014), identified regionally ( This mechanism of sand liberation from a pyroclastic deposit, detected to be operating in the present-day Amazonian climate on Mars, also likely operated over much of Martian history. ...
Dark, windblown (eolian) sand on Mars has produced significant geologic effects throughout Martian history. Although local and regional sand sources have been identified, a primary origin, or genesis, for Martian sand has not been demonstrated. This knowledge gap was recently heightened by the discovery of widespread sand motion, implying breakdown of grains to sub-sand sizes. To address the question of sand genesis, we investigated the source(s) of sand in Aeolis Dorsa (AD), the westernmost Medusae Fossae Formation, using comparisons to sand potentially sourced from multiple regions, each connoting a different sand genesis. Our methods included comparison of (1) AD sand mineralogies with those of possible sand source features, and (2) mapped AD sand deposits and inferred emplacement directions with modeled sand deposit locations and transport pathways. The results point to a time-transgressive unit, interpreted as pyroclastic, as a source of dark sand. High-resolution images of this unit reveal outcrops with dark sand weathering out of lithified bedrock. Given the extent of interpreted pyroclastic deposits on Mars, this sand genesis mechanism is likely widespread today and operated throughout Martian history. Whereas this work identified olivine-rich sand, a range of original pyroclastic lithologies would account for the mineralogic variability of dune fields on Mars. These findings can be tested through analyses of other pyroclastic deposits and potentially by data from the NASA Curiosity rover in nearby Gale crater.
... exist within the NPLD (Bouška & Bell III, 1993;Kerber et al., 2012), orbital investigations of the composition of the NPLD have focused on hydrated minerals (B. H. Horgan et al., 2009;Massé et al., 2010Massé et al., , 2012 and ice grain size (Calvin et al., 2009), so it is unknown whether or not the NPLD contain primary mafic silicates that could indicate dateable volcanic or impact deposits. ...
... Some mafic sediments at the NPLD could also be ash deposits sourced from volcanic eruptions. While the existence of volcanic edifices in the northern lowlands is controversial (Garvin et al., 2000), more distant sources could also have deposited ash, transported by atmospheric suspension and dispersed to distant locations by global atmospheric circulation (Kerber et al., 2012). Volcanic tephra can be crystalline or glass-rich, where glass abundances are significantly enhanced by water/ice interactions during eruption (Henderson et al., 2021;Wall et al., 2014). ...
... However, coarse (sand and larger) tephra is only deposited close to the source. Climate models suggest that only the finestgrained volcanic ash (particle size ∼1 μm) can be latitudinally transported from the mid-latitudes and beyond to the poles, especially at low modern atmospheric densities (Kerber et al., 2012). Since no known major volcanoes are located at northern high-latitudes, any volcanic ash in the NPLD will account for a very small volume of sediment relative to the full stratigraphy (Kerber et al., 2012). ...
Plain Language Summary
Mars' north polar cap accumulated over last few millions of years due to seasonal buildup of frost trapping atmospheric gases and incoming sediments, thereby preserving the history of Mars' recent climate in the form of an ice‐rich geologic record. Characterizing the contents of these deposits is essential to understand the role of geologic and climatic processes recently active on Mars. The Mars scientific community recommends robotic exploration of these icy north polar deposits to sample the ice and extract climate records. This study uses a novel technique to determine the composition of sediments entrained in ice by analyzing the properties of reflected light from the icy surface which is captured using an imaging spectrometer from orbit. A diverse suite of iron‐bearing minerals are detected within sediments eroding from the icy deposits, which we hypothesize were sourced from recent impacts and volcanic eruptions that deposited sediments over the north polar region. Therefore, processes like impacts and volcanism influenced the formation of the north polar deposits. Because the sediments from these sources are dateable, they can be used to determine the age of its ice‐rich climate records and thus the timescales of climate change on another planet.
... Contrary to common usage of the term in Mars geoscience [72,225,[234][235][236][237], the friability of a rock cannot be detected using satellite or aerial images. The geological term, friable, refers to rock that crumbles or sheds small fragments (such as sand grains) as a result of rubbing by human touch. ...
... Some investigators have considered, too, the possibility that fine, Martian tephra has been deposited far from a source vent following aeolian suspension [234,236,380]. The most prominent and persistent interpretation of such materials is that of the yardangforming rocks of the Medusae Fossae Formation [303,305,[380][381][382], which we discuss in Section 4.2.3. ...
... The proximity of the rocks to the volcanoes and lava flows of the Tharsis, Amazonis, Elysium, Apollinaris, and Cerberus Fossae regions provide the necessary volcanic context (Figure 39a). Further, models of possible tephra dispersal patterns [236,380] suggest that a relation between the volcanoes and the Medusae Fossae Formation is possible. However, the interpretation that the rocks consist of primary volcaniclastic material conflates two topics that should be considered separately: (1) the depositional processes and settings recorded by the rocks, and (2) the genesis of the clasts that compose the rocks. ...
Sedimentary rocks provide records of past surface and subsurface processes and environments. The first step in the study of the sedimentary rock record of another world is to learn to recognize their occurrences in images from instruments aboard orbiting, flyby, or aerial platforms. For two decades, Mars has been known to have sedimentary rocks; however, planet-wide identification is incomplete. Global coverage at 0.25–6 m/pixel, and observations from the Curiosity rover in Gale crater, expand the ability to recognize Martian sedimentary rocks. No longer limited to cases that are light-toned, lightly cratered, and stratified—or mimic original depositional setting (e.g., lithified deltas)—Martian sedimentary rocks include dark-toned examples, as well as rocks that are erosion-resistant enough to retain small craters as well as do lava flows. Breakdown of conglomerates, breccias, and even some mudstones, can produce a pebbly regolith that imparts a “smooth” appearance in satellite and aerial images. Context is important; sedimentary rocks remain challenging to distinguish from primary igneous rocks in some cases. Detection of ultramafic, mafic, or andesitic compositions do not dictate that a rock is igneous, and clast genesis should be considered separately from the depositional record. Mars likely has much more sedimentary rock than previously recognized.
... Given its regional extent, spanning >2,500-km, a volcanic provenance of the unit would be indicative of voluminous explosive volcanism. However, this explanation remains unconfirmed because it has two important deficiencies: (a) logical source(s) (Kerber et al., 2012) and (b) direct evidence of volcanic deposits. ...
... Michalski and Bleacher (2013) present evidence for large calculated erupted volumes, collapse, low relief, and resurgent domes consistent with terrestrial explosive calderas. If these features are indeed explosive calderas, ash dispersion modeling (e.g., Glaze and Baloga, 2002;Kerber et al., 2012;Keber, Forget et al., 2013;Keber, Michalski et al., 2013) suggests extensive ash deposits, carried by ancient winds, should be common throughout Arabia Terra. The kilometer-deep canyon walls within the fretted terrain should therefore expose evidence for Noachian-Hesperian era volcanic deposits. ...
... Modeling shows that the thin atmosphere on Mars today would limit ash dispersion distances (Glaze & Baloga, 2002). However, due to a thicker than present-day atmosphere (e.g., 0.5-bar) on ancient Mars, ash fall deposits would have had a wider distribution than for a similar eruption on Earth (e.g., Brož et al., 2021;Glaze & Baloga, 2002;Kerber et al., 2011Kerber et al., , 2012Wilson & Head, 2007). Therefore, in Arabia Terra, ash fall deposits would be expected to be found >1,000 km from source, that is, throughout the region. ...
Several large paterae in Arabia Terra are suggested to be calderas that produced colossal explosive eruptions (i.e., supereruptions). If these features are indeed explosive calderas, dispersion modeling suggests extensive ash deposits should be common throughout the region. However, such deposits have not previously been linked with the suggested calderas. Here, we describe layered deposits containing minerals both consistent with and diagnostic of altered volcanic ash throughout Arabia Terra. These deposits include Al‐dominant minerals such as montmorillonite, imogolite, and allophane among others. Altered ash deposits are found to thin (from 1‐km to 100‐m thickness) away from the suggested calderas. We estimate that the volcanic ash observed in Arabia Terra is the result of between 1,000 and 2,000 individual explosive eruptions over 500‐million years. Our observations support the hypothesis that Arabia Terra hosted supereruptions in the late Noachian‐early Hesperian that repeatedly blanketed the region with layers of ash.
... Depending on the size of the pyroclasts the material can fall out from the plume close to the vent or be transported far away from the vent by the wind (e.g., Parfitt and Wilson, 2008 and references therein). The fallout from these plumes can give rise to unconsolidated airfall pyroclastic deposits, which can be spread over hundreds or thousands square kilometres (e.g., Kerber et al., 2012). ...
... Black crosses and white asterisks indicate the locations shown in Fig. 8 and 9, respectively. Red dots mark potential centers of explosive volcanism as mentioned in the references listed in Table 1 Tanaka (2000) and Kerber et al. (2012). to dominantly effusive eruptions may have occurred over time (e.g., Carr et al., 1977;Greeley and Spudis, 1981;Williams et al., 2007 and references therein). ...
... The volcano may have released more than 10 15 kg of water vapour into the atmosphere during its activity and large amounts of pyroclasts. Large-scale explosive eruptions of this kind may have been responsible for extensive pyroclastic deposits on Mars (Kerber et al., 2012), such as the Medusae Fossae Formation (MFF) located on the northern and eastern flanks of this volcano and described in detail below in Section 3.2.3. III. ...
Decades of space exploration reveal that Mars has been reshaped by volcanism throughout its history. The range of observed volcanic landforms shows that effusive and explosive eruptions have occurred, albeit unevenly in time and space. Evidence for explosive volcanism—characterized as eruptions in which magma is disrupted by the expansion of dissolved gases or by an interaction of magma with external volatiles—is less common than evidence for effusive activity. Nonetheless, indications of explosive volcanism have been identified. Examples include old, rimless depressions, termed paterae, often on the summits of broad topographic rises with very gentle flanks, which are located mainly around the Hellas impact basin. Fields of kilometre-sized cones are interpreted as scoria cones, tuff rings and tuff cones. Also, extensive clusters of sub-kilometre pitted cones in the northern lowlands are proposed to be rootless cones, i.e. constructional features caused by accumulation of volcanic fragments. Finally, layered deposits widely spread in equatorial areas (e.g., the Medusae Fossae Formation), and layered stacks of ash and a putative volcanic bomb observed by rover, also point to a protracted history of explosive volcanism on Mars. Yet some of these interpretations remain a matter of scientific debate. The discovery of evidence for explosive volcanism on Mars triggered an interest in the theoretical aspects of such volcanism under gravitational and atmospheric conditions different from those on Earth. These studies indicate that explosive eruptions on Mars would behave differently from their terrestrial counterparts. This is because a lower atmospheric pressure and gravity can affect all stages of the eruption including the ascent of magma, the process of degassing and magma fragmentation, the transport and deposition of the pyroclasts, and, in some cases, the formation of explosive volcanoes themselves. On Earth, explosive eruptions are responsible for the formation of most volcanoes on land, and so the relatively sparse occurrence of explosive volcanism on Mars is surprising, especially considering the martian environmental conditions as well as wide occurrence of external volatiles on Mars. This is because the lower atmospheric pressure than on Earth ought to favour magma fragmentation and hence the formation of pyroclasts and associated explosive volcanic edifices, even if lower volumes of dissolved gases were present in martian magma than is usual on Earth. The relative dearth of explosive activity on Mars therefore represents a gap in our understanding of martian volcanism, suggesting that there may be considerable compositional differences between Mars and Earth or that evidence of explosive volcanism on Mars manifests differently than on Earth. Understanding these differences is important, as explosive volcanism provides insight into the planet’s composition and plays a crucial role in the evolution of a planet’s atmosphere by the release of magmatic gases, which have the ability to affect geological and even biological processes operating on the surface. In this paper, we present an overview of explosive volcanism on Mars—from both observational and theoretical perspectives—and discuss the implications of explosive eruptions for the evolution of the Red Planet.
... The dark protruding layer appears to be the exposed volcanic plains. Candidate origins for the light surface layer include (a) fluvial flood plain from valley networks debouching into the Arabia terra plain (e.g., Davis et al., 2019), (b) impact ejecta, (c) volcanic tephra airfall (Kerber et al., 2012), (d) dust storm airfall, and (e) sublimation residue from dust associated with regional plateau glaciation snowfall (see Madeleine et al., 2009). The fluvial flood plain origin can be excluded due to the lack of evidence for regional overland flow and the very locally distributed branched fluvial channels. ...
... Impact ejecta up to 300 m thick over an extensive area seems unlikely, but may locally contribute to the light surface layer. In addition, volcanic tephra and dust storm airfall are not expected to form such voluminous ash accumulations in the Arabia Terra region (Kerber et al., 2012). Consequently, the preferred origin that fits the observations and can explain the majority of the several hundred meters thick light surface layer is a sublimation residue associated with Amazonian plateau glaciation snowfall (Madeleine et al., 2009). ...
The Ismenius Lacus region of Mars has a diverse geological history, and we present the first high‐resolution map of Deuteronilus Cavus (36.2°N; 14.0°E, ∼120 km diameter) in the fretted terrain south of the dichotomy boundary. Strong evidence suggests a volcanic origin of the regional plains, based on the ∼50 m thick volcanic bed underlying 180–300 m of sublimation residue associated with Amazonian plateau glaciation. Pervasive external volcanic flooding, internal erosional modification, and enlargement of a pre‐existing crater by up to 175%–200% resulted in the cavus' present shape. The phyllosilicates detected within Deuteronilus Cavus could be primary materials associated with the surficial aqueous activity, subsurface alteration products excavated by impacts, or a combination of both. We observe branching fluvial channels that are more recent than the traditional valley networks and may be related to fretted terrain resurfacing during the waning period of a high‐obliquity glaciation phase. This is consistent with our interpretation of the ∼600 m thick lobate and lineated deposits, which are remnants of receding glaciers. The glacial ice, protected by a 15–20 m insulating layer of debris cover, is of significant interest for future landing missions because of its potential to preserve biological and climatological signatures, to provide a critical test of Amazonian plateau glaciation, and to be used for in situ resource utilization. With our detailed geological mapping, we improved our understanding of the geological evolution and climatic conditions in the enigmatic fretted terrain near the dichotomy boundary.
... Explosive volcanic eruptions were likely frequent during the Noachian and Hesperian periods (Wilson & Head, 2007). This study uses a map of deposits identified in the literature as potentially pyroclastic that are larger than 10 5 km 2 (Broz et al., 2020;Kerber et al., 2012;Tanaka, 2000). The mapped deposits include Arabia deposits, Electris deposits, Medusae Fossae Formation (MFF), Dorsa Argentea Formation, Hellas deposits, Argyre deposits, Tyrrhena Patera deposits, and Isidis deposits. ...
... The zeolite mineral analcime was first detected in the west of Nili Fossae in craters near the Antoniadi basin and in the eastern portion of the Arabia Terra by Ehlmann et al. (2009) using CRISM data. Ash dispersion modeling (e.g., Kerber et al., 2012Kerber et al., , 2013 suggests that extensive ash deposits should be common in the Arabia Terra. Fassett and Head (2007) observed that hundreds of meters of material was deposited on the surface of the northeast Arabia Terra, likely as airfall. ...
The evolution of the climate and hydrochemistry of Mars is still a mystery but it must have been at least occasionally warm and wet to have formed the ancient fluvial and lacustrine landforms observed today. Terrestrial examples and geochemical modeling under proposed early Mars conditions show that zeolite minerals are likely to have formed under alkaline (pH > 8) conditions with low water/rock ratio and surface temperatures below 150°C. The identification and spatial association of zeolites on the surface of Mars could thus be used to reconstruct the paleoclimate, paleohydrochemistry, and geological evolution of some locations on Mars. Previous studies identified the zeolite analcime and discuss the difficulties of identifying other zeolite species on the surface of Mars using orbital spectroscopy. We used published global mineralogical, geological, geomorphological, hydrological, physical, and elemental abundance maps and the locations of hydrous minerals detected and mapped using orbital data to create a map that delineates favorable areas to look for zeolites on Mars. We used the data‐driven fuzzy‐based Weights‐of‐Evidence method to identify and map favorable areas for zeolites on the surface of Mars up to ±40° latitude toward the poles. The final map shows that the eastern and western Arabia deposits, some sites in the Medusae Fossae formation, and some areas within and near Valles Marineris, Mawrth Vallis, highlands north of Hellas, and the Terra Cimmeria and Terra Sirenum regions would be favorable areas to look for zeolites using targeted orbital spectral analysis or future in situ observations.
... The need for more reliable methods to understand their distribution and formation processes, particularly at a regional scale, is vital to the future of Mars exploration. A variety of processes and depositional regimes, both sedimentary and volcanic, have been proposed to explain ELD formation and include lacustrine (Day et al., 2019;Lucchitta, 2010;Wharton et al., 1995;Wray et al., 2011), groundwater upwelling (Allen & Oehler, 2008;Andrews-Hanna et al., 2010;Franchi et al., 2014;Pondrelli et al., 2015Pondrelli et al., , 2019Rossi et al., 2008), ash fall (Fassett & Head, 2007;Fueten et al., 2014;Kerber et al., 2012;Le Deit et al., 2013;Schmidt et al., 2018), diapiric uplift (Jackson et al., 2011), dust rich glaciers (Bennett & Bell, 2016;Fergason & Christensen, 2008;Michalski & Niles, 2012), aeolian deposition (Annex & Lewis, 2020;Kite et al., 2016Kite et al., , 2013Lewis & Aharonson et al., 2014;Hayes et al., 2011), and a combination of multiple processes (Bennett & Bell, 2016;Cadieux & Kah, 2015;Fueten et al., 2014;Le Deit et al., 2013;Schmidt et al., 2018;Zabrusky et al., 2012). These sedimentary deposits are widespread and their occurrence in AT was first identified by Malin and Edgett (2000). ...
... Perhaps many separate eruptions occurred and were part of a long duration of volcanic activity in which ash did not fill the craters entirely and were only deposited on the plateau in sporadic patches. The Syrtis Major volcanic province makes a strong candidate for the location of such eruptions, however based on pyroclastic ejecta modeling, ash from Syrtis Major would not have been distributed in the study area (Kerber et al., 2012). In order to refine the ash fall origin hypothesis, modeling predictions must coincide with these craters, or an undiscovered buried volcanic province is the source. ...
An extensive distribution of water‐altered equatorial layered deposits (ELDs) characterizes the densely cratered terrain of Arabia Terra (AT), Mars. The majority of these deposits reside within craters and are easily identified by laterally continuous layering. The processes that led to their formation have been widely investigated, but remain unresolved. Furthermore, their precise spatial distribution as a whole, as well as their relationship to one another individually, has yet to be fully appreciated. This work examines 1,013 craters and emphasizes 45 that were observed to contain ELDs within the eastern half of AT. We present the statistical relationships between crater characteristics (e.g., location, diameter, depth), as well as evidence supporting a southeast‐northwest facies change. The 30–2,000‐m range of measured deposit thicknesses, accompanied with individual layer thicknesses, correlate with crater elevation either due to water level differences within craters, or a proximal‐distal relationship to the source. Air fall or fluid expulsion appear to stand out among all the prevailing depositional hypotheses, however the volume required to fill these craters in an ash fall scenario is in opposition with the locations of known volcanic provinces and the volume of ash that volcanic eruptions produce. This new evidence of a regional facies change provides a unique opportunity to better understand past climate and sedimentary processes on Mars, as well as the putative groundwater level in ancient AT. Ultimately, our results do not agree well with a unified depositional method for these deposits and the possibility of mixed origins should be taken seriously.
... On Mars, orbital and in situ data suggest occurrences of pyroclastic deposits, implying that explosive processes might have happened frequently throughout Mars history (Hynek et al., 2003;Loizeau et al., 2007;Lewis et al., 2008b;Kerber et al., 2012). The olivine-rich unit's extent and thick beds imply that the hypothetical explosive eruption(s) that formed the unit would have produced a volume of material similar to terrestrial Plinian supereruptions (Mastin et al., 2014). ...
... The olivine-rich unit's extent and thick beds imply that the hypothetical explosive eruption(s) that formed the unit would have produced a volume of material similar to terrestrial Plinian supereruptions (Mastin et al., 2014). From what we observe today, the most significant source -important enough to produce a widespread amount of deposits -is the Syrtis Major volcano (Kerber et al., 2012), in a potential early explosive phase. Yet, the source(s) might just as easily be covered today by more recent terrains or eroded, making it impossible to clearly identify from orbit. ...
L’exploration spatiale de la planète Mars sera marquée dans la prochaine décennie par une étape historique : l’exploration in situ de terrains d’âge noachien, soit faisant partie des plus anciens de la planète. Les sites d’atterrissage sélectionnés, le cratère Jezero et Oxia Planum, présentent depuis l’orbite les traces d’une activité hydrologique ancienne, ainsi qu’un potentiel exobiologique. Les deux rovers envoyés pour explorer ces sites (Perseverance par la NASA, et Rosalind Franklin par l’ESA et Roscosmos), sont équipés des premiers spectromètres de réflectance visible et proche-infrarouge (VNIR) à toucher le sol martien, alors que cette technique de détection est la première utilisée depuis l’orbite pour détecter et cartographier les minéraux en surface. Nos travaux de thèse sont découpés en deux axes : dans un premier temps, une analyse des deux sites d’atterrissage par télédétection a été effectuée, afin d’avancer sur leur caractérisation géologique et minéralogique. Dans un second temps, des roches terrestres analogues aux sites d’atterrissage ont été collectées et analysées à l’aide d’un spectromètre de réflectance dont le faisceau d’analyse est comparable en taille à celui de la voie VNIR du spectromètre SuperCam du rover Perseverance. Notre analyse sur le site d’atterrissage de Perseverance a permis de carter les variations minéralogiques d’une des unités géologiques les plus étendues sur le site, l’unité à olivine et carbonate, de proposer une origine pyroclastique, et d’en dater la mise en place il y a 3,82 +/- 0,07 Ga. Cet âge pourra être utilisé dans l’optique du retour des échantillons collectés par Perseverance, afin de calibrer la chronologie martienne. Là où le site d’atterrissage de Rosalind Franklin apparaît spectralement homogène depuis l’orbite, nous montrons qu’il existe à haute résolution une diversité morphologique, compositionnelle et minéralogique au sein des argiles présentes sur le site, cibles principales de la mission. Au cours de ces travaux de recherche, nous avons produit une base de données spectrale sur des échantillons analysés en laboratoire. Cette base de données inclut le premier panel représentatif de météorites martiennes, des roches terrestres naturelles dont la composition minéralogique a pu être estimée grâce à la diffraction de rayons X, ainsi que des mélanges synthétiques de composition simplifiée et de minéralogie directement transposable à celle estimée sur les sites d’atterrissage. Ces spectres de réflectance pourront être directement et automatiquement comparés à ceux mesurés sur des affleurements rocheux in situ
... On Mars, orbital and in situ data suggest occurrences of pyroclastic deposits, implying that explosive processes might have happened frequently throughout Mars history (Hynek and Phillips, 2003;Loizeau et al., 2007;Lewis et al., 2008;Kerber et al., 2012). The olivine-rich unit's extent and thick beds imply that the hypothetical explosive eruption(s) that formed the unit would have produced a volume of material similar to terrestrial Plinian super-eruptions (Mastin et al., 2014). ...
... The olivine-rich unit's extent and thick beds imply that the hypothetical explosive eruption(s) that formed the unit would have produced a volume of material similar to terrestrial Plinian super-eruptions (Mastin et al., 2014). From what we observe today, the most significant source -important enough to produce a widespread amount of deposits -is the Syrtis Major volcano (Kerber et al., 2012), in a potential early explosive phase. Yet, the source(s) might just as easily be covered today by more recent terrains or eroded, making it impossible to clearly identify from orbit. ...
The Nili Fossae region of Mars exhibits from remote sensing spectral data the largest exposures of olivine-rich materials on the planet. However, it is not clearly constrained how and when these terrains formed. Some of the proposed scenarios favor a mode of formation closely related to Isidis impact basin: either under intense effusive volcanism following the impact, from cooling of an immediate impact melt sheet or silicate impact vapor condensate. These deposits might also be pyroclastic products ejected from now eroded or buried vents. Recent studies also proposed that lag deposits could be responsible for enrichment in olivine after deposition. In this contribution, we mapped the olivine-rich unaltered and altered bedrock exposures using near infrared and thermal inertia data, investigated the geometry and key contacts of the olivine-rich unit, and determined its surface age using crater counts and stratigraphical relationships. We find that the olivine-rich bedrock extends over at least ~18,000 km2 in the Nili Fossae region, with a large part of it being unaltered. Olivine-rich material that overlaps the northern rim of Jezero crater corresponds to a primary deposit (i.e. rather than reworked material). Since this crater is younger than Isidis, we favor the hypothesis of a post-Isidis origin, rather than the impact melt (consistently with Bramble et al., 2017) and impact condensate origin. Based on our observations and crater counts, we estimate an emplacement age of 3.82 ± 0.07 Ga (Mid to Late Noachian). We discuss the origin of the unit, with the most likely scenarios being ash falls and/or pyroclastic surges. To explain the circum-Isidis distribution of these deposits, we favor the hypothesis of a thinned and weakened crust in the region subsequently to the giant impact of Isidis, as suggested by Tornabene et al. (2008). Finally, the distribution of altered bedrock conflicts with the contact metamorphism scenario. As the olivine-rich unit exposed at Jezero crater, future home of the Mars 2020 rover, is a regional stratigraphic marker, return samples for precise dating of this unit should be made one of the major mission targets.
... The MFF exhibits highly eroded surfaces, abundant yardangs, linear dunes, and various etched terrains [Bradley et al., 2002;Mandt et al., 2008;Zimbelman and Griffin, 2009;Zimbelman and Scheidt, 2018]. The proximity of Apollinaris Mons to the nearby MFF deposits suggests it may have been the source for other nearby regions that have materials with similar characteristics [Kerber et al., 2011[Kerber et al., , 2012. Recent bulk density estimates of MFF materials indicate a dry porous unit with no internal ice [Ohja and Lewis, 2018], further supporting the presence of pyroclastic deposits possibly sourced from Apollinaris Mons. ...
... Compared to both early and more current geologic maps of Mars and Apollinaris Mons [Scott and Tanaka, 1986;Greeley and Guest, 1987;Scott et al., 1993;Tanaka et al., 2014], our results indicate that Apollinaris Mons is one of several paterae on Mars with a significant period of erosion up to the end of the Early Amazonian. The erosional evidence for pyroclastic materials at Apollinaris Mons and other Martian paterae such as Tyrrhenus, Hadriacus, and Alba Montes [Reimers and Komar, 1979;Greeley, 1993, 2007;Hodges and Moore, 1994;Scott and Tanaka, 1986;Greeley and Guest, 1987;Scott et al., 1993;Kerber et al., 2012;Tanaka et al., 2014] demonstrates the importance of explosive volcanism in planetary evolution and the potential contribution of pyroclastic materials to the inventory of mobile, fine-grained surficial deposits. ...
We have utilized THEMIS, MOLA, CTX and HiRISE data sets to investigate the morphologic and topographic characteristics of the northeast flank of Apollinaris Mons, a region with evidence for significant erosion of volcanic deposits. Using ArcGIS software, we mapped the geology of the northeast flank and obtained age estimates using crater size-frequency distributions from crater counts. Of the eight mapped units, three (Apollinaris Mons upper, mid-, and lower flank units) represent volcanic flank materials in various states of preservation. The Late Noachian-Early Hesperian upper flank unit is massive and contains joint-like vertical structures along the scarp faces of two large plateaus whose upper surfaces likely represent the original surface or near-surface deposits of Apollinaris Mons. Downslope-facing plateau scarps have up to 500 m of relief. Positioned below this unit are the mid-flank and lower flank units, each representing eroded surfaces within Apollinaris Mons flank materials that have stabilization ages between the Late Hesperian to Early Amazonian. Mantling material in the region contains cavities and boxwork-like textures that resemble patterns in terrestrial eroded pyroclastic flow deposits. Dome-shaped mounds west of the mapping region have morphologic similarities to terrestrial fumarolic mounds or possibly inverted impact craters. Both the texture and features suggest widespread pyroclastic deposits adjacent to Apollinaris Mons. Using MOLA gridded topography, we estimate that ~308 km³ of materials have been eroded along the flanks of the volcano. Statistical and histogram data from the thickness values of eroded materials shows that up to ~300 m of material has been removed from the majority of flank surfaces. Assuming steady state erosion of flank surfaces, we estimate an area-normalized loss rate of ~0.859 nm/yr for northeast Apollinaris Mons. This erosion rate is within the long-term range for Mars (~0.01–10 nm/yr) as estimated from MER landing site geology by Golombek et al. [2006].
... Finally, evidence to date is equivocal that the unit was deposited as spherules from other large impacts (Edwards and Christensen, 2011), eroded and transported epiclastic sediment, or air-fall pyroclasts ( Rogers et al., 2018). Based on previous interpretations of abundant pyroclastic rocks on Mars (e.g., Kerber et al., 2012;Bandfield et al., 2013) and in situ observations of martian pyroclastic rocks (Squyres et al., 2007), including olivine-rich ash (Ruff et al., 2014), we undertake a detailed geomorphic and stratigraphic study to test whether the unit may have been deposited as volcanic ash. ...
... Errors are generally small (Table DR4 [ Models of explosive eruptions on Mars imply that >0.5-mm-diameter ash would have been capable of traveling hundreds of kilometers from vents in the greater Syrtis-Isidis region under a thicker early martian atmosphere (Wilson and Head, 2007), but not thousands of kilometers to the greater Syrtis-Isidis region from volcanoes elsewhere on Mars (Kerber et al., 2012). Thickness data leave the exact provenance ambiguous, and source vents have potentially been degraded by ~3.6 b.y. of erosion or covered by the extensive lavas that emanated from Syrtis Major and filled Isidis Planitia (Fig. 1), consistent with recent discoveries of poorly exposed volcanoes elsewhere on Mars (Xiao et al., 2012;Michalski and Bleacher, 2013). ...
... Fallout of ash is an alternative to fallout of dust. 3D ash-dispersal simulations suggest that distalash fallout in Gale crater would correlate with distal-ash fallout in Aeolis Dorsa (Kerber et al. 2011(Kerber et al. , 2012. Landscape-terrain feedbacks can explain preferential preservation of rhythmite and/or ash on preexisting local-to-regional topographic highs such as Mt. ...
Unraveling the stratigraphic record is the key to understanding ancient climate and past climate changes on Mars. River deposits when placed in stratigraphic order could constrain the number, magnitudes, and durations of the wettest climates in Mars history. We establish the stratigraphic context of river deposits in Aeolis Dorsa sedimentary basin, 10E of Gale crater. Here, wind has exhumed a stratigraphic section of >=4 unconformity-bounded sedimentary rock packages, recording >=3 distinct episodes of surface runoff. Early deposits (>700m thick) are embayed by river deposits (>400m), which are in turn unconformably draped by fan-shaped deposits (<100m) which we interpret as alluvial fans. Yardang-forming deposits (>900 m) unconformably drape all previous deposits. River deposits embay a dissected sedimentary-rock landscape, and comprise >=2 distinguishable units. The total interval spanned by river deposits is >(1x10^6-2x10^7) yr; more if we include alluvial-fan deposits. Alluvial-fan deposits unconformably postdate thrust faults which crosscut river deposits. We infer a relatively dry interval of >4x10^7 yr after river deposits formed and before fan-shaped deposits formed. The time gap between the end of river deposition and the onset of yardang-forming deposits is constrained to >10^8 yr by the density of impact craters embedded at the unconformity. We correlate yardang-forming deposits to the upper layers of Gale crater's mound (Mt. Sharp/Aeolis Mons), and fan-shaped deposits to Peace Vallis fan. Alternations between periods of low vs. high mean obliquity may have modulated erosion-deposition cycling in Aeolis. This is consistent with results from an ensemble of simulations of Solar System orbital evolution and the resulting history of Mars obliquity. Almost all simulations yield intervals of continuously low mean Mars obliquity that are long enough to match our unconformity data.
... Ancient volcanic eruptions on Mars have been modeled with the potential to produce regional-globally extensive airfall deposits (Brož et al., 2021;Kerber et al., 2011;Whelley et al., 2022). Modeling has previously suggested that distal pryoclasts from large-scale volcanic provinces could have been dispersed over Arabia Terra (Kerber et al., 2012). However, a more local source of volcaniclastic material could be paterae that have been suggested to be remnant volcanoes. ...
Oxia Planum, Mars, is the future landing site of the ExoMars Rosalind Franklin rover mission, which will search for preserved biosignatures in a phyllosilicate‐bearing unit. Overlying the mission‐important phyllosilicate‐bearing rocks is a dark, capping unit—known here as the Low albedo, Thin, Resistant (LTR) unit—which may have protected the phyllosilicate‐bearing unit over geologic time from solar insolation and radiation. However, little is known about the origin of the LTR unit. Here, we map the LTR unit and investigate its distribution and morphology across 50,000 km² using a variety of orbital remote sensing data sets. The characteristics of the LTR unit include draping palaeo‐topographic surfaces, deposition over a wide elevation range, and a consistent vertical thickness that can be best explained by airfall deposition including a primary or reworked volcanic palaeo‐ashfall. Previous research suggests that the LTR unit was not significantly buried, and we find it to be preferentially preserved with a high mechanical strength in discrete deposits representing palaeo‐topographic lows. We suggest this could be attributed to localized cementation via upwelling groundwater. This scenario suggests that most of the phyllosilicate‐bearing exposures may not have been protected over geologic time, as the uncemented LTR sediment would have easily been removed by erosion. However, our observations indicate that the scarped margins of the LTR unit deposits probably exposed regions of the once protected phyllosilicate‐bearing unit. These areas could be key science targets for the ExoMars Rosalind Franklin rover mission.
... In addition, the region contains evidence for an ancient Martian sea approximately three times the size of the modern Caspian Sea on Earth with associated widespread alteration and hydration of the crust 33 . Though this part of Terra Cimmeria and Terra Sirenum is recognized for having some volcanic vents and structures 6,28,31,34,35 , the provenance of olivine-rich flood lavas and the widespread (1.8 × 10 6 km 2 ), voluminous (∼10 6 km 3 ) 'Electris' suite of airfall deposits 28,36 remains enigmatic 37 . This work describes a diverse suite of volcanic structures and associations of those structures with tectonics and crustal properties. ...
The relatively well-preserved ancient crust of Mars provides a natural window into early planetary evolution not available on Earth due to sustained tectonic recycling and erosion on this planet. Mars has generally been considered a one-plate basaltic planet, though recent evidence suggests magmatic evolution resulting in felsic crust might have occurred sporadically. Here we show multiple lines of evidence for diverse volcanism and complex volcanotectonics in the southern highlands of Mars within and around the ∼3.5–4-billion-year-old Eridania basin. Infrared remote sensing reveals bimodal volcanism consisting of olivine-bearing basalts and voluminous, widespread dacitic (64–69% SiO2, and possibly higher) volcanic deposits within a region of high crustal potassium. The diverse igneous compositions are associated with an extraordinary number and morphological range of volcanic structures, including domes, stratovolcanoes, calderas and pyroclastic shields occurring proximal to large (hundreds of kilometres in diametre) basins within the Eridania region. The 2–4 km-deep topographically concave-up basins have crustal thicknesses 10–20 km thinner than adjacent terrain and disrupt patterns of deeply seated remnant crustal magnetism. The Eridania basins may represent ancient episodes of crustal recycling via lithospheric delamination in which altered, hydrated volcanic materials were cycled downward and melted resulting in magmatic evolution analogous to pre-plate tectonic processes on the Archaean Earth.
... The origin of the water and sediment for surface runoff is unclear, but the widely accepted theory is that the light-layered deposits in Valles Marineris are sedimentary, formed by fluvial processes. Another theory holds that the light-layered deposits result from pyroclastic materials interacting with water ( Milliken et al., 2008 ;Kerber et al., 2012 ;Mishev and Smith, 2021 ). It was proposed that a wetter climate during the Hesperian period favoured the formation of light-toned deposits on Mars ( Flahaut et al., 2010a , b ). ...
... Second, if the sediments that became the Burns formation were initially emplaced on Meridiani as airfall deposits as proposed for the diagenetic scenario, then it could reinforce other geologic evidence that pyroclastic ash deposits are widespread on the surface of Mars and may be responsible for many large-scale layered units (e.g., Hynek et al., , 2003Kerber et al., 2011Kerber et al., , 2012Le Deit et al., 2010;Michalski & Bleacher, 2013;Ojha & Lewis, 2018;Scott & Tanaka, 1982). Moreover, the diagenetic scenario may illustrate one pathway by which materials originally deposited by airfall became transformed and sulfate-enriched, which could aid in the interpretation of other sulfate-bearing layered deposits that might have had a similar origin (e.g., Chojnacki Fueten et al., 2011;Le Deit et al., 2010;Weitz et al., 2011Weitz et al., , 2012. ...
The sulfate‐rich sandstones of the Burns formation investigated by the Opportunity rover on Meridiani Planum, Mars, are directly underlain by the fine‐grained sedimentary rocks of the Grasberg formation. It was recently shown that, except for differing amounts of MgO and SO3, the Burns and Grasberg rocks have very nearly the same chemical composition, suggesting that both units may be genetically related. Here, quantitative models demonstrate that the chemical composition of the Burns rocks is closely reproduced by the addition of MgO and SO3 to a Grasberg‐like precursor. Comparison with previously proposed chemical models indicates that this new model reproduces the measured Burns rock compositions far better than evaporite models and somewhat better than the addition of sulfur alone to pristine basalt. Based on this result, we propose that the precursor materials for both units were derived from related sources and initially had very similar (or identical) chemical compositions, but magnesium sulfate salts were added to the Burns formation during diagenesis. We further propose an alternative origin of the Burns sandstones that incorporates this new chemical model, which involves (a) deposition of fine‐grained airfall deposits with a composition similar to that of Grasberg, (b) induration and erosion into sand‐sized particles, (c) reworking and deposition of the sand grains by eolian and fluvial processes, and (d) diagenetic alteration of the resulting sediments that includes enrichment in MgO and SO3 through evaporation or freezing of infiltrating groundwater. This new scenario would have substantially different implications for sediment sources, depositional history, and diagenetic processes than other proposed scenarios.
... Explosive eruptions on Mars have been proposed to have formed tholi, small cones, ancient calderas in the southern highlands, and to have been involved in the construction of large shields in Tharsis (Brož et al., 2015(Brož et al., , 2021Kerber et al., 2012;Werner, 2009). Explosive eruptions at the calderas of the Circum-Hellas Volcanic Province, including Tyrrhena, Hadriaca, Malea, and Pityusa Paterae, were suggested to be related to rapid magma ascent from deep-seated sources associated with crustal fracturing, as a result of the formation of the Hellas impact basin (Bernhardt & Williams, 2021aGregg & Williams, 1996). ...
Plain Language Summary
Perhaps the most recognizable image of a volcano is a topographic rise, such as a cone or mountain, flanked by lava flows. While this image fits many volcanic settings on Earth and Mars, many known volcanic settings on Earth do not fit this iconic description at all and the question remains open as to whether that exception might also be true for Mars, where observations are limited to remote sensing interpretations. Several volcanoes in Arabia Terra on Mars lack recognizable topographic features, suggesting an important form of explosive volcanism associated with crustal collapse. These source vents could have produced huge amounts of ash airfall deposits, now widely observed throughout the region as layered deposits. These features are likely more common on Mars than is currently recognized and are likely a critical component of Mars' geologic puzzle. This work describes in detail the geological characteristics of Eden Patera (a large caldera with diameter over 60 km), located within Arabia Terra on Mars. This site is a “type‐locality” to which other collapsed calderas on Mars can be compared. Mapping results from Eden Patera illuminate a complex geologic history driven by both explosive (ash‐dominated) and effusive (lava‐dominated) eruptions.
... Therefore, in regions which have been subjected to high degrees of aqueous alteration, significant fractionation of K from Th would occur, resulting in a K/Th ratio that is lower than the martian global average . We use such trends to investigate if aqueous alteration is a dominant process within SCR, a trend that would arise if NW Arabia functioned as a sedimentary basin or floodplain, suggested by previous studies Kerber et al., 2012;Tanaka, 2000). ...
An area roughly 9 × 10⁵ km² within northwest Arabia Terra contains several depressions interpreted to be supervolcanic calderas, contained within a chemical province considered consistent with large-scale igneous processes. Despite the underlying global significance to climate and geology, the supervolcanic hypothesis is yet to be tested with comprehensive compositional or geophysical analyses. Here we present geochemical evidence consistent with regional-scale supervolcanic resurfacing, with associated eruptions capable of degassing a climate-altering ∼10⁸ kg of sulfur phases. Through gravitational modeling, we find evidence of low-density pyroclastic loading within this region, and a low elastic thickness, suggestive of a higher heat flow during the eruptive process. Our geochemical observations within this region reinforce its compositional uniqueness compared to contemporaneous volcanoes.
... In all these cases, a sequence of lava flows is a possible source of reflectors, similar to the terrestrial large flow fields where separate episodes of volcanism produced overlapping lava flows of similar composition, but perhaps having different properties such as a low or high fraction of vesicles or a layer of ash, regolith, or some amount of weathering during a hiatus that creates a density contrast (Morgan et al., 2015). Multiple lines of evidence support the hypothesis that the Tharsis Montes have been past sources of explosive volcanism, producing tephra and ash that may have been deposited throughout the Province and across the surface of Mars (e.g., Edgett, 1997;Ganesh et al., 2020;Hynek et al., 2003;Kerber et al., 2012;Mouginis-Mark & Zimbelman, 2020). Pyroclastic deposits could also be generated by the numerous low shield fields and fissures mapped by Richardson et al. (2021). ...
The Tharsis Montes volcanoes on Mars are the source of laterally extensive lava flows and other volcanic deposits generating a complex stratigraphy throughout the Tharsis Volcanic Province. We use SHAllow RADar (SHARAD) and Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) observations in a region northwest of Ascraeus Mons to determine the composition, density, thickness, and spatial distribution of these emplaced volcanic materials. We identified subsurface reflectors along 43 SHARAD and five MARSIS observations. Reflectors in the volcanic plains are interpreted to be sequences of basaltic lava flows with interspersed pyroclastic material, dust, or regolith during a hiatus in activity. Others correspond to the base of three major flow fields. Several plain reflectors were detected by both MARSIS and SHARAD. Other notable reflectors were identified near Ascraeus' flank where lava buried glacially derived sediment. We derived thickness and other material properties for flows using their distinct topographic boundary visible in the radar images. Permittivity ranged from 7.0 to 11.2 corresponding to lava flow densities of 3.20–3.52 g/cm³. Flow thicknesses ranged from 19.8 to 60.2 m. Loss tangents were low for the flow fields ranging from 0.024 to 0.043. Loss tangents in the plains ranged from 0.010 to 0.076. Higher loss tangents correspond to lossier regions that may have higher concentrations of radar absorbing minerals like hematite. Surface roughness controls where reflectors are detected. SHARAD detects the base of three out of the four flow fields in this region with muted surface roughness from dust mantling and erosion.
... Analogously, many terrestrial loess deposits show signs of being derived from erosion of shales and other fine-grained sedimentary rocks as second-generation sediments (Muhs, 2018). The MFF deposit emplacement has been dated to Mars's Hesperian period ($ 2.9-3.7 Gyr ago), which was characterized by strong volcanic activity and catastrophic flooding on an otherwise dry planet (Kerber et al., 2012;Zimbelman and Scheidt, 1683), but its origin is still a matter of debate. Recent gravity measurements found that the unit is dry and porous, consistent with pyroclastic ashfalls and flows . ...
The Martian dust cycle is the primary driver of atmospheric and surface variability in the arid, low-surface pressure climate of present-day Mars. Martian dust is ubiquitous across the surface, produces Mars's characteristic rusty color, and, in the modern era, may derive primarily from one huge, wind-eroded sedimentary deposit. Lofted dust absorbs solar radiation, increasing atmospheric temperatures, and emits thermal radiation, warming the surface at night. Rearrangement of surface dust via dust lifting and deposition modifies albedo, hence patterns of surface heating. Strong winds and dust devils are likely the main causes of dust lifting, although it is unknown whether most dust is lifted directly by winds (as individual grains or aggregates) or via saltation of sand-sized particles. Other key unknowns include threshold wind stresses for particle motion, how dust fluxes relate to atmospheric conditions, and how dust is transported through the boundary layer. Positive feedbacks between dust lifting, radiative heating, and circulation strength and surface winds give rise to rapid increases in dust lifting that produce dust storms. Some storms remain local and only last a few sols, others expand to become regional, while global storms are produced by multiple regional storms merging and/or new lifting sites developing across Mars. Global storms, which last several Earth months and occur three times per Mars decade on average, have the greatest impact on climate: strengthening the global circulation, modifying atmospheric waves, and transporting more dust and water vapor to high altitudes. Yet the strong interannual variability in storm occurrence, onset timing, and location, remain poorly understood. Improved observations of dust lifting, boundary layer processes, and ice nucleation on dust particles, plus greater understanding of the role of surface dust availability and dust-ice coupling, are needed to better represent major storms in Mars climate models. Monitoring the evolution of dust storms continuously and simultaneously at global scale from orbit is required to better understand the processes and feedbacks responsible for their growth and decay. In addition, such observations are needed to provide initial conditions for future Mars weather forecasting systems.
... Thus, it is reasonable to conclude that much of the post-impact-event fill within the larger crater is likely to be some combination of sediment and impact-generated debris, and perhaps tephra. Sediment and impact debris could have been locally-or regionally derived or carried to the site by wind; tephra would have to have been created some distance away and transported to the site in suspension (e.g., Kerber et al., 2012). Locally derived sediment would include clastic debris eroded from the rim and wall of the larger, older crater; these sediments would be coarser at the base of the crater walls and potentially finer toward the crater center. ...
Ripples, transverse aeolian ridges (TARs), and dark‐toned sand sheets and dunes are common aeolian bedforms on the Martian surface. They are important for understanding the nature of present‐day Martian sediments and regional aeolian processes. Here we present a case study investigation of ripples, TARs, a dark‐toned sand sheet, and dunes in an unnamed—but well‐covered by remote sensing datasets—crater in Terra Sabaea, Mars, to consider their nature and possible origin scenarios. Repeat high‐spatial resolution images show only minor albedo changes among the dark‐toned sand dunes but no obvious changes in the ripples and TARs. Visible and infrared spectra show that the megaripples and TARs are pyroxene‐bearing, while the dark‐toned sheet and dunes are olivine‐bearing. Thousands of TARs are superimposed on the crater walls, and they have a similar composition as the bedrock exposed around the central pit, suggesting that some percentage of the sediment composing the TARs may be locally derived. Megaripples have a similar composition as TARs, suggesting they may share a similar origin. Dark‐toned sand sheets and sand dunes show a different composition from the substrate of the crater, plus bedform orientations indicative of a dominant, north‐northwest wind, indicating that some of these dark sands might have been blown in from outside of the crater. Alternatively, the sand in the megaripples, TARs, sand sheets, and dunes could share a common source, and some or even all of them could be recycled from the weathering and erosion of the sand‐bearing clastic rocks exposed in the crater walls.
... Furthermore, at least one distinct layer of dark sand or dust crops out along the flanks of unit Hs in some locations, indicating mafic fines were entrained in the depositional stack of the unit. Ash deposits erupted by the volcanic centers in the MPR stand to reason because atmospheric flow models by Kerber et al. (2012) showed that ash plumes from Pityusa or Malea Paterae would be entrained in the south polar vortex, thereby depositing ash around the entire pole, covering the area of today's DAF. We also suggest these fines to contribute to the dune fields found throughout the MPR and eastern Noachis Terra (see unit Add interpretation). ...
Characterized by large paterae and late Noachian wrinkle-ridged plains, the ~1.2 million km² Malea Planum region (MPR) has been grouped into a circum-Hellas volcanic province and likely represents the oldest of the large volcanic areas on Mars. Being key to Mars’ early volcanic, tectonic, and climate evolution, we conducted a comprehensive and in-depth photogeological investigation of the MPR using multiple datasets including THEMIS-IR as a basemap. We identified 26 geomorphologic units and derived apparent model ages based on crater size-frequency distribution measurements for six of them. Along with stratigraphic, morphologic, hyperspectral, and gravimetric analyses, as well as findings by previous works in the surrounding regions, our chronostratigraphy resulted in a complete landscape formation model of the mapping area. At 3.9–3.8 Ga, Malea and Pityusa Paterae form, probably as volcanic collapse calderas geographically controlled by Hellas-concentric faults. Pityusa Patera hosts folded, layered deposits, possibly pyroclastics emplaced and shortened during patera formation as a piston-type caldera. Around 3.8–3.7 Ga, i.e., during the same time the ridged plains of the Hellas basin are formed, up to ~3.9 million km³ of volcanic and clastic/ballistic deposits partially sourced by Pityusa/Malea Patera activity and/or by now-obscured vents are emplaced and superpose Pityusa and Malea Paterae, thus covering any potential features associated with them. Simplistically assuming the wrinkle-ridged plains to entirely consist of basaltic deposits with ~2 wt% H2O, outgassing might have produced ~0.8 m Global Equivalence Layer of water and/or 3.9 hPa of H2, which could have temporarily increased ambient temperatures, potentially enabling fluvial and lacustrine processes across the Malea-Hellas regions. After plains emplacement, doming above a shallow magma chamber and its subsequent partial evacuation forms Amphitrites Patera as a caldera on a ~1.5 km high, broad rise collocated with a positive ~2.6 x 10⁻³ m/s² free-air, but no significant Bouguer gravity anomaly. Smooth crater fills throughout the area that often show high thermal inertias as well as enrichments of plagioclase and clay minerals (probably from leaching) might represent pyroclastic deposits resulting from this patera formation. Between 3.7 and 3.6 Ga, the northern slope of Amphitrites Patera is heavily dissected by low-viscosity flow processes that drain towards the Hellas basin floor and leave behind the Axius Valles amongst others, forming one of the densest martian valley networks with a drainage density of ~0.08 km⁻¹. 1,777 km long Mad Vallis and other smaller channels traversing the entire MPR and connecting the South Pole area with the Hellas basin are also formed around this time. Based on the geologic context and feasibility studies, we favor glacial meltwater/mud or alternatively low-viscosity lavas sourced from Amphitrites’ summit over a catastrophic sapping event as causes for the Axius Valles. Following this, the Barnard impact event deposits ejecta on the surrounding flow features southeast of Amphitrites Patera. Relatively shortly after its formation, sinuous valleys and ridges are formed in Barnard crater, likely by meltwater from ice sheets that might also have occupied Amphitrites Patera. Around 3.5 Ga, approximately 80-140 m (i.e., up to ~140,000 km³) of layered, friable materials are emplaced across large parts of the MPR as far north as 60°S. These materials are an extension of the circum-south polar Dorsa Argentea Formation (DAF) and possibly originate as lag deposits from wet-based glaciation. Entrained within these deposits are dark, fine-grained materials, likely pyroclastics potentially sourced from volcanic activity at Peneus Patera, which might have formed around the same time, with bounding faults penetrating the wrinkle-ridged plains but without completely resurfacing its interior floor. Combining structural analyses of radial wrinkle ridges within Peneus Patera with a piston-type caldera model similar to Pityusa Patera (Bernhardt and Williams, 2021) would imply the collapse of a magma chamber at 19.5 to 26 km depth, i.e., potentially in the mid-crust. Another, distinct set of up to ~210,000 km³ of friable airfall deposits, possibly sourced by ongoing/recurring Peneus activity, then cover the entire MPR but are relatively quickly eroded except where they are armored by superposing impact ejecta, thus forming numerous pedestal craters. In the Amazonian, these pedestals are themselves covered by up to few 10s of 1000s of km³ of atmosphere-derived volatiles and fines, which are then also sculpted into a second, distinctly younger pedestal crater population. Observable ongoing erosion of pyroclastic materials entrained in DAF deposits across the MPR and elsewhere provide mafic fines that potentially supply the formation of vast, mostly transversal and barchanoid dune fields in local depressions, e.g., within Pityusa Patera and on the floors of larger impact craters throughout the MPR and Noachis Terra to the northwest, which is contrary to previous theories of more local supplies. In conclusion, our in-depth investigation of the MPR, which included a comprehensive map and chronostratigraphic as well as morphometric analyses, shows that the area experienced a complex volcanic, tectonic, eolian as well as most likely (glacio-)fluvial history and acted as corridor between the south polar area and the Hellas basin. In total, ~294,000 km³ of material were eroded from the MPR in multiple episodes, i.e., not just in in one catastrophic event. This might have contributed close to a third of the originally one million km³ of hummocky materials residing on the Hellas basin floor (Bernhardt et al., 2016a). Unlike Olympus Mons in the Tharsis region (Zuber and Mouginis-Mark, 1992) but similar to Pityusa Patera, Peneus Patera formed as relatively deep-seated caldera. Activity related to Amphitrites and Peneus Paterae likely contributed to ridged plains formation and the associated volatile release as well as mobilization had significant environmental effects on the southern hemisphere.
... Recent work suggests that the presence of massive ice, rather than simply pore-filling ice, challenges current thermal models that predict any near-surface ice should be geologically young and actively retreating in the current climate (Bramson et al. 2017). The composition and origin of the Medusae Fossae Formation (MFF) are also contested, with different approaches offering contradictory interpretations as to whether the unit is a friable ash deposit or if it may offer an equatorial deposit rich in water ice, or possibly both (e.g., Bradley et al. 2002;Watters et al. 2007;Mandt et al. 2008;Carter et al. 2009;Kerber et al. 2012;Campbell & Morgan 2018;Wilson et al. 2018;Ojha & Lewis 2018;Campbell et al. 2021). In the north polar layered deposits (PLD), a sequence of recent layers has been identified and suggested to be related to obliquity variations over the last 370 ka (Smith et al. 2016). ...
The Mars Orbiter for Resources, Ices, and Environments (MORIE) was selected as one of NASA's 2019 Planetary Mission Concept Studies. The mission builds upon recent discoveries and current knowledge gaps linked to two primary scientific questions: (1) when did elements of the cryosphere form and how are ice deposits linked to current, recent, and ancient climate, and (2) how does the crust record the evolution of surface environments and their transition through time? Addressing these questions has emerged in numerous recent reports as a high priority in investigating the evolution of Mars as a habitable world. A subsidiary goal of the mission concept is to provide information relevant to the eventual human exploration of Mars, specifically helping to locate and quantify near-surface water ice and hydrated mineral resources. The proposed instrument suite includes polarimetric synthetic aperture radar imaging, radar sounding, high-resolution visible and infrared imaging, both short-wave and thermal-infrared spectroscopy, and multichannel wide-angle imaging. MORIE would provide novel measurements of Mars expected to lead to significant new discoveries by the first radar imaging from orbit, radar sounding directly over the poles, and mineral mapping at spatial scales that will unravel geologic sequence stratigraphy through time. The final report of the mission concept provides details on the spacecraft, orbital design, technological maturity, results from systems-level integration studies, and costs. This article is intended to expand upon the science motivation for the mission, the measurement goals and objectives, and the instrument trade space that was examined in detail during the concept study.
... both processes resulting in crater floor shallowing. Explosive volcanic eruptions on Mars are known to produce widely dispersed tephra (e.g., Kerber et al., 2012) and potentially significant deposits on crater floors (e.g., Le Deit et al., 2013). With the exception of the deposition of the distal ash layer, magmatic processes are not known to have influenced the evolution of the Ries crater. ...
Since its recognition as an impact structure 60 years ago, no volcanics were anticipated in the circular depression of the 14.8 Ma old Nördlinger Ries. Here, we describe for the first time a volcanic ash‐derived clinoptilolite‐heulandite‐buddingtonite bed within the 330 m thick Miocene lacustrine crater fill. Zircon U‐Pb ages of 14.20 ± 0.08 Ma point to the source of the volcanic ash in the Pannonian Basin, 760 km east of the Ries. The diagenetically derived zeolite‐feldspar bed occurs in laminated claystones of the Ries soda‐lake stage and represents the first unequivocal stratigraphic marker bed in this basin, traceable from marginal surface outcrops to 218 m below surface in the crater center. These relationships demonstrate a deeply bowl‐shaped geometry of crater fill sediments, not explainable by sediment compaction and corresponding stratigraphic backstripping alone. Since most of the claystones formed at shallow water depths, the bowl‐shaped geometry must reflect 134 +23/−49 m of sagging of the crater floor. We attribute the sagging to compaction and closure of the dilatant macro‐porosity of the deeply fractured and brecciated crater floor during basin sedimentation and loading, a process that lasted for more than 0.6 Myr. As a result, the outcrop pattern of the lithostratigraphic crater‐fill units in its present erosional plane forms a concentric pattern. Recognition of this volcanic ash stratigraphic marker in the Ries crater provides insights into the temporal and stratigraphic relationships of crater formation and subsidence that have implications for impact‐hosted lakes on Earth and Mars.
... Such observations of Mars confirmed in a variety of studies the eruptive styles to be mainly effusive while having the resemblance of large shield volcanoes, with several volcanic cones, like cinder cones among others identical to those of Galapagos or Hawaii (Brož and Hauber, 2012;Ghent, Anderson, and Pithawala, 2012;Gulick and Baker, 1990). They also display shallow flanks, which were interpreted to be composed of pyroclastic deposits, mainly deposited by airfall (Brož and Hauber, 2012;Gregg and Farley, 2006;Kerber, Head, and Madeleine, 2011;Kerber, Head, and Madeleine, 2012). ...
Volcanic cinder, also known as scoria, is an extrusive igneous rock that forms when gas-rich magmas of basaltic or andesitic composition cool quickly. It is typically dark in color, ranging from black to red depending on its chemical composition. Sometimes fresh cinder samples show a variety of shiny metallic colors on its surface ranging from blue to gold to silver. The origin of these colors has remained unknown up to now. Cinder samples from an eruptive event occurred in October 2005 have been collected in the surroundings of the Sierra Negra volcano in the Galápagos Islands. The samples’ crystallographic structure, chemical composition, and surface morphology have been analyzed using X-Ray diffractometry (XRD), energy dispersive X-Ray spectroscopy (EDS) and a field gun emission scanning electron microscopy (SEM), respectively. Based on an extensive physical and chemical analysis, we were able to demonstrate that these colors are due to a light interference phenomenon. These results have a great potential to be used for a wide variety of purposes such as determining the temperature and composition of magma and evaluating volcanic samples for planetary studies.
... Lower atmospheric pressure in the Hesperian and Amazonian would have enhanced eruptions' explosivity even in basaltic magmas with lower volatile contents (Wilson & Head, 2007). Under low atmospheric pressures, tephra and ash would have dispersed onto the surface at distances much greater than on Earth (Wilson & Head, 1994); thus, explosive eruptions may have emplaced many of the regional-scale sedimentary deposits on Mars (Kerber et al., 2012). ...
Abstract Orbital imagery and spectroscopy at Mars have identified a variety of deposits potentially consistent with volcanic tephra formed during explosive volcanic eruptions, and some of these deposits may have formed due to water‐ or ice‐magma interactions during phreatomagmatic eruptions. If this is the case, these deposits could serve as an additional record of past water on Mars. Previous work has demonstrated that phreatomagmatic tephra is characterized by much lower crystallinities than tephras from other types of eruptions. We hypothesize that crystallinity could be inferred remotely using spectroscopy; however, tephra spectral properties have not been directly linked to their mineralogy. Here, we use Mars analog tephra samples to investigate if eruption styles and the past presence of water during the eruption of possible volcanic deposits on Mars can be determined using orbital spectroscopy. Visible/near‐infrared (VNIR) reflectance and thermal infrared (TIR) emission spectra were collected of basaltic volcanic tephras sourced from a range of eruption styles and deposit types on Earth. Our research demonstrates that, TIR and VNIR data are both sufficient to detect increased glass abundances in volcanic deposits, potentially indicating volatile interactions during an eruption, and that glass‐poor tephras have distinct TIR properties that can be used to infer tephra type (e.g., ignimbrite vs. scoria). Combining VNIR and TIR orbital data for analysis based on our new laboratory spectral endmember library may allow a reevaluation of Martian volcanic and volatile histories using current and future planetary orbital and in situ spectral datasets.
... There is significant global evidence of explosive volcanism on Mars (e.g., Broz & Hauber, 2012), and ash falls have been suggested as a likely depositional mechanism for other layered deposits on Mars (Kerber et al., 2011(Kerber et al., , 2012, including in the eastern Medusae Fossae Formation, which hosts polygonal ridges interpreted as filled fractures (Kerber et al., 2017) that have similarities to those within the NE Syrtis layered sulfates. While Syrtis Major is mostly an effusive basaltic province (Hiesinger & Head, 2004), there is significant evidence that Nili Patera in its center hosted major pyroclastic eruptions (e.g., Fawdon et al., 2015). ...
Ancient stratigraphy on Isidis Basin's western margin records the history of water on early Mars. Noachian units are overlain by layered, basaltic composition sedimentary rocks that are enriched in polyhydrated sulfates and capped by more resistant units. The layered sulfates—uniquely exposed at northeast Syrtis Major—comprise a sedimentary sequence up to 600 m thick that has undergone a multistage history of deposition, alteration, and erosion. Siliciclastic sediments enriched in polyhydrated sulfates are bedded at meter scale and were deposited on slopes up to 10°, embaying and thinning against preexisting Noachian highlands around the Isidis Basin rim. The layered sulfates were modified by volume loss fracturing during diagenesis. Resultant fractures hosted channelized flow and jarosite mineral precipitation to form resistant ridges upon erosion. The structural form of the layered sulfates is consistent with packages of sediment fallen from either atmospheric or aqueous suspension; coupling with substantial diagenetic volume loss may favor deepwater basin sedimentation. After formation, the layered sulfates were capped by a “smooth capping unit” and then eroded to form paleovalleys. Hesperian Syrtis Major lavas were channelized by this paleotopography, capping it in some places and filling it in others. Later fluvial features and phyllosilicate‐bearing lacustrine deposits, sharing a regional base level of ∼−2,300 m, were superimposed on the sulfate‐lava stratigraphy. The layered sulfates suggest surface bodies of water and active groundwater upwelling during the Noachian‐Hesperian transition. The northeast Syrtis Major stratigraphy records at least four distinct phases of surface and subsurface aqueous activity spanning from late Noachian to early Amazonian time.
... One of the biggest ongoing changes in our view of Mars is the recognition of the dominance of sedimentary processes over coherent bedrock (e.g., lava) on the surface. Recent investigations of the ancient southern highlands using morphology, mineralogy, thermal properties, and superposition relationships have shown that friable, layered rocks are much more common than previously thought (Edgett 2016;Rogers et al. 2017), and when combined with known regional sedimentary layered deposits like Arabia Terra, Meridiani Planum, etc. (e.g., Malin and Edgett 2001;Lewis et al. 2008;Kerber et al. 2012), these observations suggest that Mars has had extremely active sedimentary cycle. Indeed, many weathering sequences possibly indicative of paleosols are associated with sedimentary units (Noe Dobrea et al. 2010;Carter et al. 2015). ...
This report requested by the International Mars Exploration Working Group (IMEWG). Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re‐evaluate and update the sample‐related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub‐objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others.
The search for life on other planets is one of the most important scientific challenges of this century, centered mainly on Mars. The Atacama Desert is one of the places on the planet with an environment similar to the red planet, with a hyper-arid core that constitutes an extreme environment and scarce life, due to environmental factors. At the moment it has not been possible to confirm the existence of life in this planet, but it is planned to take the life to this planet by means of potato crop. Also has been research the application of microorganisms for the recovery of desert soils, with high salinity or low fertility, through the interaction of microorganisms and plants. The present review describes the similarities between the La Joya desert in Atacama and Mars, showing its importance for the search for life on that planet. Show the recent advances in the investigation of potato crops for its development on Mars or in similar conditions, in addition to the importance of the application of microorganisms that facilitate the growth and adaptability of this crop to inhospitable conditions.
In an attempt to improve the quality of the seismic signals provided by the seismometer of the InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) on Mars, part of the tether linking the seismometer to the InSight lander was buried by some regolith using the scoop of the articulated robotic arm. The regolith in a source area was scraped into piles, scooped and dumped by the scoop from a height of ∼50 cm above the surface onto the tether. Part of the regolith was carried away by the wind and dispersed 1–2 m downwind, as evidenced by the comparison between images taken from the lander before and after the regolith pouring. Using both ballistic trajectory and wind dispersion effects as a sorter, the grain size range was determined through numerical fluid mechanics simulations. The trajectory of the poured grains is determined by the Martian atmospheric and gravimetry conditions, the initial conditions of scoop pouring and grain lithology. The spatial grain distribution on the ground shows a downwind decrease in grain size from the pouring point, with a size ranging from 1 mm near the dump point to ∼100 μm at the farthest area observed on the images. We find that the deposit of grains coarser than 500 μm is controlled mainly by gravity. Grains finer than 100 μm are present in the regolith, but they are not quantifiable with this method because they are blown away by the wind.
Plain Language Summary
Despite years of orbital observations of the surface of Mars, mid‐to low‐latitude layered deposits (LD) in Arabia Terra are not yet fully understood. These deposits record an important geological sequence of the early Martian history, but their exact formation, specifically the putative role of the water in their formation and preservation, remains an unanswered question. This study helps in further understanding these processes by comparing and contrasting LD present in craters in very close proximity to each other. In this way, proposed hypotheses benefit from having a control that is not limited to a singular crater or location. Our study contributes to the understanding of regional geological processes in Arabia Terra revealing long‐term aqueous activity. Results combine various analyses, including measurements of layer thickness and attitudes, orbital spectroscopy, basin geometry, and morphologies aimed at reconstructing the geological evolution of the area. In particular, we interpreted that LD were emplaced in a depositional environment reflecting sediment accumulation strongly controlled by a regional groundwater reservoir in acidic conditions.
Much has been discovered about volcanism on Mars over the past fifty years of space exploration. Previous reviews of these discoveries have generally focused on the volcanic constructs (e.g., Olympus Mons and the other volcanoes within the Tharsis and Elysium regions), the analysis of individual lava flows, and how this activity has evolved over time. Here we focus on attributes of volcanology that have received less attention and build upon characteristics of terrestrial volcanoes to pose new questions to guide future analyses of their Martian equivalents either with existing data sets or with new types of measurements that need to be made. The remarkable lack of exposed dikes at eroded ancient volcanoes attests to an internal structure that is different from terrestrial equivalents. Enigmatic aspects of the origin of the ridged plains (commonly accepted to be volcanic but with few identifiable flow fronts and only rare vents), the style(s) of volcanism during the earliest period of Martian history (the Noachian), and the possible mode(s) of formation of the Medusae Fossae Formation are considered here. Martian meteorites have been dated and are volcanic, but they cannot be correlated with specific geographic areas, or the chronology of Mars derived from the number of superimposed impact craters. Some of these questions about Martian volcanism can be addressed with existing instrumentation, but further progress will most likely rely on the acquisition of new data sets such as high-resolution gravity data, the return of samples from known localities, the flight of a synthetic aperture imaging radar, penetrators sent to the Medusae Fossae Formation, and detailed in situ field observations of selected volcanic sites.
Wherever effusive volcanism has occurred, there is usually also evidence of explosive volcanism. The boundaries between these two kinds of eruption are blurred, because even the sources of lava flows, regarded as the classic effusive landform, may exhibit explosive activity. In the absence of an atmosphere, the expansion of gas (derived from volatiles either dissolved in or encountered by the magma) is uninhibited once any bubbles have burst, and explosively ejected particles of all sizes follow ballistic trajectories once they are clear of any gas jet. An atmosphere impedes bubble expansion, decelerates smaller ballistic particles preferentially compared with larger ones, and introduces the possibility of a convective plume (i.e., an eruption column) able to loft fine particles to much greater heights than would be possible ballistically. Atmospheres also enable the formation of ground-hugging pyroclastic density currents that have no equivalents on airless bodies.
This chapter explores the various hypotheses put forward for the formation of the Martian dichotomy, the topographic difference between the northern lowlands and the southern highlands of the planet. Among the various hypotheses, the Southern Polar Giant Impact (SPGI) was the only one validated with the discovery of twelve volcanic alignments as predicted by the 3D model. Furthermore, this hypothesis is the only one that matches both astronomical and geophysical data available in the literature and all the requirements to be seriously considered as a theory. The various volcanic centres of Mars, including the vast majority being part of the alignments, are described with full detail in this chapter.
Lava tubes exists as volcanic features not only on Earth, but even on other worlds. Lava tubes are the most practical and effective places where to install the first human bases on Mars. We review the human to Mars architectures currently being developed, subsequently we describe a context for the use of lava tubes for human habitation. The architecture for the use of in-situ resources as fuel for a return rocket, the use of a landing vehicle as the initial habitat are discussed. Also, the core landing site selection criteria are discussed, including how the access to a lava tube might change the landing approach. Additionally, the challenges to constructing a larger scale habitat for a growing population necessary to achieve a permanent base and the possible solutions are proposed. Whether lava tubes are present on the Martian surface, the shielding effect that they can provide is exceptionally advantageous in both logistical and economical terms for a planetary mission, since they do not require a huge mass load to be brought on a space mission and minimize considerably the work to be done on the dangerous Martian surface after landing—however, habitats on the surface still need to be considered where lava tubes are absent. Lava tubes can naturally protect from deadly radiations, extreme temperature variations, dust storms, and micrometeorite impacts. Thermal mining inside lava tubes is proposed as a realistic way to extract water ice from below the surface and use it for living purposes. Robots and humans should work together in order to detect and access the best lava tube close to the selected landing site. Lava tubes on Earth or the Moon can result in a great opportunity for conducting analog Martian missions.
Highland paterae are broad, low-sloped volcanoes on Mars that have a large summit caldera and channeled flanks. Crater-modeled ages suggest they may represent some of the oldest central vent volcanoes on the planet. The presence of channeled flanks that surround a younger summit caldera with topographically smooth floor material has led to the interpretation that highland paterae record a transition from explosive volcanic eruptions to more effusive eruptive styles. In this chapter we describe the geology of seven highland paterae (Amphitrites Patera, Peneus Patera, Malea Patera, Pityusa Patera, Tyrrhena Patera, Hadriaca Patera, and Apollinaris Mons), discuss what that reveals about their history and origin, and then discuss possible avenues of future research on these intriguing Martian landforms.
ExplosiveExplosive volcanism on Mars volcanism should be the most common style on a planet characterized by a low atmospheric pressure and by an assumed high volatile content. However, the observations of the surface of Mars show how explosive volcanism is not widespread as it should be in a planet with the above mentioned characteristics. Therefore, one of the two characteristics should be missing. Considering that the atmospheric pressure has been more or less the same all over the Martian history, then the obvious conclusion is that Mars never had such an high volatile content. Yet, low contents of volatile can still trigger explosive volcanism in the low pressure environment of Mars and this is the reason why several pyroclastic deposits have been observed on the surface of the Red Planet.
Distributed‐style volcanism is an end member of terrestrial volcanism that produces clusters of small volcanoes when isolated magma bodies ascend from broad magma source regions. Volcano clusters can develop over millions of years, one volcano at a time, and can be used to infer unobserved geologic phenomena, including subsurface stresses and cracks during eruption periods. The Tharsis Volcanic Province covers approximately one‐quarter of the martian surface and hosts a large concentration of small volcanoes that formed from distributed volcanism. We present a catalog of 1,106 small volcanic vents identified within Tharsis Volcanic Province. This catalog includes morphologic measurements for each cataloged vent. Vent lengths range from 71 m to 51 km, widths range from 40 m to 3.1 km, and 90% of vents have lengths at least 1.5 times their widths. Additionally, 90% of edifices associated with vents have topographic prominences <100 m. Vents are found throughout Tharsis, though they generally form clusters near large volcanoes or among large graben sets. Older regions with volcanic eruption ages of >1 Ga are found at the Tharsis periphery in the Tempe‐Mareotis region and Syria Planum. Vents in the Tharsis interior have reported ages <500 Ma. Regional trends in vent orientation and intervent alignment are dependent on nearby central volcanoes and fossae. We use these findings to hypothesize that within the most recent 500 Ma, magma was present under and to the east of the Tharsis Montes and that some of this magma erupted and built hundreds of small volcanoes in this region.
Compositional stratigraphy, generally composed of Al-rich clay minerals overlying Fe/Mg-rich clay minerals, is observed in many locations on Mars. Here we describe the occurrence of such mineralogical stratigraphy in settings where the protoliths are almost certainly pyroclastic materials. One such example includes altered rocks high on the summit and flanks of explosive volcanoes in Thaumasia Planum. These clay-bearing deposits are most consistent with precipitation-driven weathering of ash deposits. Considering explosive volcanism was pervasive in the Noachian, the early sedimentary record of Mars in some locations is likely dominated by glassy, fragmented, porous, chemically reactive materials with highly specific surface area. These pyroclastic deposits were potentially a critical geological component linking clay minerals to elements of Mars’ climate, weathering, and sedimentary puzzle.
The Tharsis Province is the largest and youngest volcanic region of Mars, and includes the giant shield volcanoes Olympus Mons and the three Tharsis Montes (Arsia, Pavonis, and Ascraeus Montes). Extensive studies of the styles of volcanic activity within Tharsis have been conducted over the past 45 years, and have identified numerous lava flows in excess of 150 km long, multiple caldera collapse events, and the possibility that explosive volcanism (perhaps due to phreatomagmatic activity) took place. Glacial and tectonic events have also been described. By virtue of the apparent age of the lava flows found in this area, the Tharsis Province is the most likely source of Martian meteorites.
To search more efficiently for a record of past life on Mars, it is critical to know where to look and thus maximize the likelihood of success. Large-scale site selection for the Mars 2020 mission has been completed, but small (meter to 10 cm) scale relationships of microenvironments will not be known until the rover reaches the surface. Over a 2 meter transect at a modern volcanic deposit on the flank of Askja volcano in the barren highlands of Iceland, we compared two biological indicators (ATP activity and 16SrRNA amplicon sequence composition) to physical characteristics including bulk chemical composition, spectral signatures of mineralogy, and grain size. Using analytical instrumentation analogous to those available on Mars rovers we were able to characterize the geological setting of the deposits and link physical parameters to microbial abundance and diversity. In general, methanogenesis, methanotrophy/methylotrophy and nitrate reduction were the functional traits most associated with microbial community shift along the transect. Core microbiome members tended to be associated with nitrate reduction, and relative abundance of core microbes were strongly related to free water in the deposit. Community compositional shift of the rare microbiome was related to microenvironmental changes such as change in grain size, geochemistry, and age of deposit. These correlations lead us to suggest a sampling strategy that accounts for Martian geology, looking for an undisturbed (not-remobilized) explosive volcanic ash below pumice could maximize diversity and abundance of different bioindicators. Our study also illustrates the importance of studying the variability across microenvironments in low bio-mass settings on Earth.
This paper describes the possible karst landforms observed in the Light Toned Deposits (LTDs) located within Cagli crater, a medium size crater located in northern Sinus Meridiani, an area near the equatorial region of Mars. A morphological and morphometric survey of the LTDs surface morphologies through an integrated analysis of the available Reconnaissance Mars Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images highlighted the presence of shallow depressions that display different shapes and sizes . The Martian landforms were interpreted as sinkhole resemble similarly karst landforms that can be observed both in different karst terrains on the Earth and in other regions of Mars. The karst landforms observed highlight the evaporitic origin of these materials and suggest both climatic change and the presence of liquid water, probably due to ice melting, during the late Amazonian period.
Hellas Planitia, located within an enclosed basin which includes the lowest topography on Mars, appears to be undergoing net erosion. Dust is removed from the basin. It probably contributes to global dust storms and should leave behind a coarse lag. The particle size distributions and particularly the rock or boulder populations in this lag might be useful for distinguishing between processes which formed the lithologic units that comprise Hellas Planitia. This report concludes that the abundance of rock particles larger than coarse sand is very low. Although this hypothesis awaits confirmation from forthcoming spacecraft data, the origins for Hellas floor deposits favored by this study are indurated volcanic airfall or ancient loess, lacustrine deposits, and some types of volcanic mud flows. The conclusions of this study tend to disfavor such geologic processes as blocky lava flows, glacial deposits (e.g., moraines), or boulder-laden catastrophic flood outwash.
The landscape of the Argyre Planitia and adjoining Charitum and Nereidum Montes in the southern hemisphere of Mars has been heavily modified since formation of the Argyre impact basin. This study examines morphologies in the Argyre region revealed in images acquired by the High Resolution Imaging Science Experiment (HiRISE) camera and discusses the implications for glacial and periglacial processes. Distinctive features such as large grooves, semicircular embayments in high topography, and streamlined hills are interpreted as glacially eroded grooves, cirques, and whalebacks or roche moutonnée, respectively. Large boulders scattered across the floor of a valley may be ground moraine deposited by ice ablation. Glacial interpretations are supported by the association of these features with other landforms typical of glaciated landscapes such as broad valleys with parabolic cross sections and stepped longitudinal profiles, lobate debris aprons interpreted as remnant debris covered glaciers or rock glaciers, and possible hanging valleys. Aligned boulders observed on slopes may also indicate glacial processes such as fluting. Alternatively, boulders aligned on slopes and organized in clumps and polygonal patterns on flatter surfaces may indicate periglacial processes, perhaps postglaciation, that form patterned ground. At least portions of the Argyre region appear to have been modified by processes of ice accumulation, glacial flow, erosion, sediment deposition, ice stagnation and ablation, and perhaps subsequent periglacial processes. The type of bedrock erosion apparent in images suggests that glaciers were, at times, wet based. The number of superposed craters is consistent with geologically recent glacial activity, but may be due to subsequent modification.
A glacial geologic interpretation was recently presented for Argyre,
which is herein extended to Hellas. This glacial event is believed to
constitute an important link in a global cryohydric epoch of Middle
Amazonian age. At glacial maximum, ice apparently extended far beyond
the regions of Argyre and Hellas, and formed what is termed as the
Austral Ice Sheet, an agglomeration of several ice domes and lobes
including the Hellas Lobe. It is concluded that Hellas was apparently
heavily glaciated. Also glaciation was young by Martian standards
(Middle Amazonian), and ancient by terrestrial standards. Glaciation
appears to have occurred during the same period that other areas on Mars
were experiencing glaciation and periglacial activity. Glaciation seems
to have occurred as a geological brief epoch of intense geomorphic
activity in an era characterized by long periods of relative inactivity.
A large number of anomalous landforms on Mars can be attributed to glaciation, including the action of ice and meltwater. Glacial landscapes are concentrated south of lat -33° and in the Northern Plains suggesting vast Austral and Boreal ice sheets. Crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in Martian history. Thus, Mars may have had a relatively warm, moist climate and dense atmosphere much later than previously believed.
1] The nature and origin of the Medusae Fossae Formation (MFF) on Mars has been debated since the return of the first Viking images. The MFF's young age, distinctive surface texture, and lack of obvious source have prompted multiple hypotheses for its origin. This study uses data from the Mars Global Surveyor (MGS) mission to examine the MFF at all available scales. We discuss and quantify observations from Mars Orbiter Laser Altimeter (MOLA) topography and Mars Orbiter Camera (MOC) images to better constrain the origin of the MFF. Topographic grid estimates yield a present extent of 2.1 Â 10 6 km 2 and a volume of 1.4 Â 10 6 km 3 ; however, remnant yardang deposits observed far from the thicker lobes of MFF material suggest that it may have once covered up to 5 Â 10 6 km 2 . We do not find compelling evidence for extensive fluvial reworking of the MFF; however, in several regions, buried channels are apparent in the MFF because the formation is draped over underlying topography. Layering is apparent at all scales, from submeter to hundreds of meters, with variable resistance to weathering. Continuity of layers appears to be local to regional, but not likely formation-wide. Yardangs form both parallel and bidirectional patterns, with resistant layers and jointing probably influencing their orientations. A comparative study of MFF regional topography and surface expression indicates that the MFF is quantitatively dissimilar to Martian polar layered deposits. The material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin.
1] New data reveal the presence of a system of parallel dune-like ridges extending in a band for up to 25– 30 km around the eastern margin of the source trough for the Mangala Valles outflow channel system. We interpret these ridges to be formed during initial phreatomagmatic activity caused by dike emplacement, cryospheric cracking, magma-groundwater mixing, and explosive eruption to the surface. The erupted material consisted of fragmented magma, steam, and country rock which expanded from a choked state at the surface vent to form a near-ballistic, Io-like eruption plume. Outward flow of the plume at velocities of 30– 60 km-long section of the graben is interpreted to have formed the system of dune-like ridges. Subsequent outpouring of groundwater formed the Mangala Valles outflow channel system.
We describe a set of two "new generation" general circulation models of the Martian atmosphere derived from the models we originally developed in the early 1990s. The two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations. The vertical resolution near the surface has been refined, and the vertical domain has been extended to above 80 km. These changes are accompanied by the inclusion of state-of-the-art parameterizations to better simulate the dynamical and physical processes near the surface (boundary layer scheme, subgrid-scale topography parameterization, etc.) and at high altitude (gravity wave drag). In addition, radiative transfer calculations and the representation of polar processes have been significantly improved. We present some examples of zonal-mean fields from simulations using the model at several seasons. One relatively novel aspect, previously introduced by Wilson [1997], is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi-global, angular-momentum conserving Hadley cell which has no terrestrial equivalent. Within such a cell the Coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km. This winter polar warming had been observed but not properly modeled until recently. In fact, thermal inversions are generally predicted above one, and often both, poles around 60-70 km. However, the Mars middle atmosphere above 40 km is found to be very model-sensitive and thus difficult to simulate accurately in the absence of observations.
1] Several zones of graben (Memnonia, Sirenum, Icaria, Thaumasia, and Claritas Fossae) extend radially away from the Tharsis rise in the southern hemisphere of Mars for distances of up to 3000–4000 km. These graben systems are commonly interpreted to be related to regional tectonic deformation of the Tharsis rise associated with either upwelling or loading. We explore the possibility that these giant Tharsis-radial graben systems could be the surface manifestation of mantle plume-related dike intrusion complexes. Emplacement of dikes causes near-surface stresses that can produce linear graben, and lateral dike emplacement related to plumes on Earth can produce dike swarms with lengths of many hundreds to several thousands of kilometers. We develop a Mars dike emplacement model and explore its implications. We find that the properties (outcrop patterns, widths, and depths) of the extensive Tharsis-radial graben systems are consistent with an origin through near-surface deformation associated with lateral propagation of magma-filled cracks (dikes) from plumes beneath Tharsis, particularly beneath Arsia Mons and Syria Planum. Such dikes are predicted to extend through the crust and into the upper mantle and can have widths of up to several hundred meters. Analyses of summit caldera complexes on Martian volcanoes imply that the magma supply from the mantle into shallower reservoirs is episodic on Mars, and we interpret the graben systems to be large swarms of laterally emplaced giant dikes resulting from the tapping of melt from episodically rising mantle plumes in a buffered magma supply situation. The magmatic interpretation of the Tharsis-radial graben potentially removes one of the conundrums of Tharsis tectonics in which it appeared necessary to require two distinct modes of support for Tharsis in order to explain the presence of radial graben on both the elevated flanks (attributed to isostatic stresses) and outside the rise (more consistent with flexure): dikes capable of forming the observed graben can be emplaced under a wide range of stress fields, including zero stress. The fact that almost no eruptive features are associated with the graben further restricts the ranges of magma density to values between 30 MPa. Eruptions from giant dikes would be more likely to occur in regions where the crust was thinner, such as the northern lowlands, providing a potential mechanism for emplacement of recently documented Early Hesperian volcanic plains (Hr) there. Dike-related graben systems represent efficient mechanisms of lateral heat transfer in the crust and near-surface environments. Lateral dike intrusions could penetrate the cryosphere and cause melting and release of groundwater, as in the Mangala Valles area, and could also drive hydrothermal circulation systems. The geometries of such dike systems will create barriers which are likely to influence regional to global groundwater flow patterns, which may help to explain the abundance of outflow channel sources in eastern Tharsis. Improved knowledge of the Martian crust and mantle density structure will help to refine this analysis and to provide estimates of the magma densities for dikes underlying specific graben.
1] Mars Orbiter Laser Altimeter (MOLA) topographic data support the presence of an extensive Hesperian-aged volatile-rich south polar deposit, the Dorsa Argentea Formation (DAF) and related deposits, underlying the present Amazonian-aged cap. The eastern margin of these deposits displays further evidence for meltback, ponding, and drainage of the volatile-rich deposit. Channels leading from the margins of the DAF deposit enter nearby craters and are interpreted to represent drainage of water, ice, and sediment from the DAF. Channels connecting these craters provide evidence for extensive crater flooding, ponding (minimum volumes 600 km and a vertical height of 2.9 Â 10 6 km 2 . Candidate top-down and bottom-up melting scenarios are examined; the presence of associated Hesperian-aged volcanic deposits and possible subglacial edifices suggests that local and regional basal heating was a major factor in generating the meltwater that formed the drainage features.
1] The geologic history of Crater Terby is developed through geomorphic and stratigraphic analyses within the regional context of the Hellas basin. Terby exhibits $2-km-thick sequences of layers that consist of repetitive, subhorizontal and laterally continuous beds. The layers are predominantly fine-grained as indicated by their ease of aeolian erosion, although a few consolidated layers weather to form rubbly talus. The grain size or composition of the deposited materials fluctuated, producing layering, but the overall properties of the deposits are similar throughout the sequence and are comparable to layered deposits in other crater basins around Hellas. The original depositional geometry, physical and geological characteristics of the layers in Terby and the other basins lead us to favor a lacustrine origin, but a loess-like origin cannot be ruled out. The formation of the layers corresponds to a period when the circum-Hellas region may have been occupied by a lake(s) up to 3.6 km deep. Once the lake in Hellas decreased, the layers in Terby were incised by troughs and a moat-like depression. We attribute this erosion to scour beneath an ice cover due to a lack of integrated fluvial drainage or large aeolian deflation features. The presence of viscous flow features in a crater on Terby's northwestern rim and lobate features on Terby's crater floor are also indicative of ice. The lack of depositional features associated with the postulated glacial activity suggests there was a contemporaneous shallow (ice-covered?) lake covering the floor of Terby that transported material into the greater Hellas basin.
Geologic mapping, thermal inertia measurements, and an analysis of the color (visual wavelengths) of the martian volcano Apollinaris Patera indicate the existence of two different surface materials, comprising an early, easily eroded edifice, and a more recent, competent fan on the southern flank. A chronology of six major events that is consistent with the present morphology of the volcano has been identified. We propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on Earth. A basal escarpment typically 500 m in relief and morphologically similar to the one surrounding Olympus Mons was produced between the formation of the main edifice and the fan, indicating multistage eruptions over a protracted period of time. Contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed Apollinaris Patera. Stereophotogrammetric measurements permit the volume of the volcano to be estimated at 105 km3. From this volume measurement and an inferred eruption rate (1.5 × 10-2 km3 yr-1) we estimate the total eruption duration for the main edifice to be ∼107 yrs. Plausible estimates of the exsolved volatile content of the parent magma imply that greater than 1015 kg of water vapor was released into the atmosphere as a consequence of this activity. This large amount of water vapor as well as other exsolved gases must have had a significant impact on local, and possibly global, climatic conditions.
Evidence is presented supporting the identification of a discrete, well-preserved air fall deposit generated by explosive volcanism on Mars. The deposit is located immediately to the west of the summit caldera of Hecates Tholus (32°N, 209°W), the northernmost of the three volcanic constructs in the Elysium Planitia region. The absence of superposed impact craters larger than the resolution limit of the Viking images (40 m per pixel) indicates a very young age for this eruption, which evidently postdates even the most recent collapse episode of the Olympus Mons caldera (∼300 m.y. B.P.; Neukum and Hiller (1981)). From the distribution of craters smaller than 2 km in diameter, it appears that the air fall material mantles an area about 50×75 km in extent to an estimated thickness of about 100 m. By adapting numerical models for terrestrial volcanic eruptions to the Martian environment, these dimensions imply an eruption cloud height of about 70 km. In order to attain such an altitude, the mass eruption rate must have been ∼107 kg/s and the volatile content either ∼1 wt % for H2O or ∼2 wt % for CO2. Although it is not possible to distinguish between silicic and basaltic volcanism on Hecates, were the volatile species CO2, the depth of most recent storage prior to eruption of the magma would have to be 50–100 km (due to the solubility of CO2 in the melt). If H2O were the driving volatile, a minimum depth of storage would be 0.2–4 km, thereby permitting the possibility of ground water assimilation by the magma.
Building on previous studies of volcanoes around the Hellas basin with
new studies of imaging (HRSC, THEMIS, MOC, HiRISE, CTX), multispectral
(HRSC, OMEGA), topographic (MOLA) and gravity data, we define a new
Martian volcanic province as the Tyrrhena-Malea Volcanic Province
(T-MVP). With an area of >2.1 million sq. km, it contains the six
oldest central vent volcanoes on Mars, which formed after the Hellas
impact basin, between 4.0 to 3.6 Ga. These volcanoes mark a transition
from the flood volcanism that formed Malea Planum ~3.8 Ga, to localized
point source eruptions. The T-MVP volcanoes have two general
morphologies: 1) shieldlike edifices (Tyrrhena, Hadriaca, and
Amphitrites Paterae), and 2) caldera-like depressions surrounded by
ridged plains (Peneus, Malea, and Pityusa Paterae). Positive gravity
anomalies are found at Tyrrhena, Hadriaca, and Amphitrites, perhaps
indicative of dense magma bodies below the surface. The lack of
shield-like edifices and weak gravity anomalies at Peneus, Malea, and
Pityusa suggest a fundamental difference in their formation, styles of
eruption, and/or compositions. The northernmost volcanoes, the ~3.7- 3.9
Ga Tyrrhena and Hadriaca Paterae, have low slopes, well-channeled
flanks, and smooth caldera floors (at tens of meters/pixel scale),
indicative of ash shields formed from poorly-consolidated pyroclastic
deposits that have been modified by fluvial and aeolian erosion and
deposition. The ~3.6 Ga Amphitrites Patera also has a well-channeled
flank, but it and the ~3.8 Ga Peneus Patera are dominated by scalloped
and pitted terrain, pedestal and ejecta flow craters, and a general
`softened' appearance. This morphology is indicative not only of surface
materials subjected to periglacial processes involving water ice, but
also of a surface composed of easily eroded materials such as ash and
dust. The southernmost volcanoes, the ~3.8 Ga Malea and Pityusa Paterae,
have no channeled flanks, no scalloped and pitted terrain, and lack the
`softened' appearance of their surfaces, but they do contain pedestal
and ejecta flow craters and large, smooth, bright plateaus in their
central depressions. This morphology is indicative of a surface with not
only a high water ice content, but also a more consolidated material
that is less susceptible to degradation (relative to the other four
volcanoes). We suggest that Malea and Pityusa (and possibly Peneus)
Paterae are Martian equivalents to Earth's giant calderas (e.g.,
Yellowstone, Long Valley) that erupted large volumes of volcanic
materials, and that Malea and Pityusa are probably composed of either
lava flows or ignimbrites. HRSC and OMEGA spectral data indicate that
dark gray to slightly red materials (often represented as blue or black
pixels in HRSC color images), found in the patera floors and topographic
lows throughout the T-MVP, have a basaltic composition. A key issue is
whether this dark material represents concentrations of underlying
basaltic material exposed by aeolian winnowing, or if the material was
transported from elsewhere on Mars by regional winds. Understanding the
provenance of these dark materials may be the key to understanding the
volcanic diversity of the Tyrrhena-Malea Volcanic Province. References
[1] Crown, D. and Greeley, R. (2007) U.S. Geol. Surv. Sci. Inves. Ser.
Map 2936. [2] Gregg, T., et al. (1998) U.S. Geol. Surv. Map I- 2556. [3]
Leonard, G. and Tanaka, K. (2001) U. S. Geol. Survey Misc. Invest.
Series Map I-2694. [4] Kolb, E. and Tanaka, K. (2008) Geologic Map of
the Planum Australe Region of Mars. U. S. Geol. Survey. Misc.
Investigation Series, in review. [5] Peterson, J. (1978) Proc. 9th LPSC,
3411-3432.
Sharply delineated closed depressions, one-half to tens of kilometers across, with 400 meters estimated maximum depth, are locally abundant in the south polar region. They indent the surface of a massive homogeneous blanket that mantles the cratered bedrock surface. Some pits extend through the blanket exposing the underlying rock floor, and, where the blanket is thin (50–100 meters), its extensive removal exposes large ares of exhumed rock floor producing a terrain described as etched. The blanketing material is speculatively interpreted to be an eolian sedimentary deposit containing a mixture of fine particulate matter, possibly including volcanic ash, and particles of frozen volatiles, principally CO2and H2O. Fields of dunes, groups of linear grooves and flutes, and an unusual scoured topography on the surface of layered blanketing material suggest strong wind action. For this reason, deflation by wind, aided by ablation (evaporation) of included frozen volatiles, is regarded as the most likely mechanism for producing the south polar pits and etched terrain. Pitted and etched terrains and the deposits into which they are cut suggest that the south polar region, and presumably the north polar area as well, have experienced alternating episodes of eolian deposition and erosion.
A global equatorial set of layered deposits on Mars has been reexamined with Mars Global Surveyor data. The stratigraphy, morphology, and erosional characteristics of units separated by thousands of kilometers are remarkably similar to each other and consistent with a widespread, episodic, subaerial source of fine-grained material. This study is the first to propose a genetic link between many units that have traditionally been considered on a local or regional level, including the Medusae Fossae Formation, Valles Marineris interior deposits, chaotic terrain, Terra Meridiani, and Arabia materials. Mapping relationships suggest that all of these units are post-Noachian in age and formation may have continued until the recent past. Thinning of deposits with increasing distance from the Tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in the Tharsis region, analogous to those produced by terrestrial plinian eruptions. Contemporary Martian winds would preferentially transport ash from an eruption plume near Tharsis east or west along the equator depending on the season. Erosion has removed much of the original volcanic ash, and only isolated layered stacks remain, sometimes in topographic depressions that inhibit erosion. Modeling indicates that widespread dispersion of ash after an eruption is easily attainable in present or past atmospheric conditions, consistent with the hypothesis that the far-reaching deposits may be composed of ash from past explosive eruptions in the vicinity of Tharsis.
Morphologic characteristics of Amphitrites and Peneus Paterae, Mars, suggest that they are unlike any other central-vent martian volcano, and may represent a distinct style of volcanism on Mars.
Several models have been proposed for the geologic evolution of the Argyre basin, Mars. We use high-resolution MOLA and MOC data in order to test the plausibility of these hypotheses.
The contrast in crustal thickness, surface age, elevation, and morphology between the southern cratered highlands and northern lowland plains of Mars is termed the crustal dichotomy. The oldest exposed sections of the crustal dichotomy boundary are ancient cratered slopes, which influenced post-Noachian fresh crater morphometry, Late Noachian valley network planform, and the degradation patterns of Middle to Late Noachian (˜3.92-3.7 Ga) impact craters. Noachian visible and topographically defined impact craters at the top of the cratered slope show no evidence of flexure-induced normal faulting. These observations and published geophysical data collectively require an Early to Pre-Noachian age for the crustal dichotomy, prior to the largest recognized impact basins. Late Noachian plateau deposits and more prolonged Tharsis volcanism appear to have buried parts of the old cratered slope, and fretted terrain developed in this transition zone during the Early Hesperian Epoch (˜3.7-3.6 Ga). Fretted/knobby terrains, lowland plains, and most visible structures (wrinkle ridges, fractures, and normal faults) postdate Noachian crater modification and are several hundred million years younger than the cratered slope of the crustal dichotomy, so they provide no valid basis or constraint for models of its formation. Long-wavelength topography in cratered terrain dates to Early to Pre-Noachian time and provides a useful model constraint. Geological and geophysical observations are thus reconciled around an early age and relatively rapid development of the Martian crustal dichotomy.
Models are presented for the physical processes that occur in the formation of pyroclastic flow generated by the gravitational collapse of a vertical eruption column. The main controlling parameters are considered to be the vent radius (R), gas content (N), and initial velocity (W) of the gas. For the ranges R=50 to 600 m, N=0.5 to 5% gas, and W=200 to 600 m/s, column collapse is modeled as an inverted turbulent jet, modified by including expressions for the efficiency of heat transfer between air and small pyroclasts. Entrainment of air during the collapse can result in initial cooling of the flow by up to 350°C. The variation in the amount of cooling is considered to account for the considerable ranges of emplacement temperatures and the widely differing degrees of welding observed in different ignimbrites. High emplacement temperatures are favored by eruption columns with low gas contents and low gas velocities, whereas low emplacement temperatures are favored by eruption columns with high gas velocities and high gas contents. The initial stages of flow are modeled as a highly turbulent, low-particle-concentration density current. Numerical solutions of the turbulent stages of flow are presented assuming uniform radial spreading from a central source (the vent). Flows from large eruptions may still have velocities of up to 100 m/s at distances of tens of kilometers from the source. The methods have also been applied to uphill flow and demonstrate that flows produced at high volume rates of eruption can surmount topographic barriers of several hundred meters at distances of several tens of kilometers from the vent and explain the spectacular mobility of some large pyroclastic flows. Turbulent suspension in a gas flow with a low concentration of particles is not a viable mechanism of particle transport, as many of the clasts (about 1 mm) found in the depositis have terminal velocities well above the shearing stress velocities of even a rapidy moving gas flow (v*=1 to 12 m/s). The flows are deduced to segregate into a high-concentration basal zone within a a few kilometers of the vent, as larger clasts settle to the base of the flows. Fines are thought to be generated by crushing within the high-concentration basal zone and are fluidized by exsolving gases to produce a pyroclastic flow with high concentrations of fluidized particles. The upper dilute part of the flow and the fine ash elutriated by fluidization contribute to the formation of widely dispersed ash fall deposits which are as voluminous as the associated ignimbrite. The flows are capable of transporting clasts of several centimeters or tens of centimeters to tens of kilometers distance. The motion of the dense lower part (the pyroclastic flow) disassociates itself from the upper turbulent cloud of fine ash and gas, which eventually mixes with the atmosphere sufficiently to form a convective plume.
A theoretical model is developed to investigate the sensitivity of buoyant atmospheric plumes to a wide range of ambient atmospheric conditions, including the temperature gradient, the latitude of the source, and the season. The formulation highlights the compressibility of an ideal gas, internal consistency between the governing equations for the conservation of momentum and energy, and the explicit use of the equation of state. Specific results are presented for water vapor plumes and implications are developed for multicomponent (water vapor, silicate particles, and condensates) volcanic plumes. -from Authors
The polar layered deposits of Mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable. These deposits appear to be hundreds of millions of years old, and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes. Possible relict dust deposits include, from oldest to youngest: Noachian intercrater materials, including Arabia mantle deposits, Noachian to Early Hesperian south polar pitted deposits, Early Hesperian Hellas and Argyre basin deposits, Late Hesperian Electris deposits, and the Amazonian Medusae Fossae Formation. These deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers. The apparent persistence of dust sedimentation at the south pole back to the Early Hesperian or earlier and the early growth of Tharsis during the Late Noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the Middle Noachian. A scenario for the overall history of dust and perhaps ice deposition on Mars includes widespread, voluminous accumulations perhaps planetwide during the Noachian as impacts, volcanism, and surface processes generated large amounts of dust; the Arabia deposits may have formed as ice availability and dust accumulation waned. During the Early Hesperian, thick dust sedimentation became restricted to the south pole and the deep Hellas and Argyre basins; the north polar sedimentary record prior to the Amazonian is largely obscured. Deposits at Electris and Medusae Fossae may have resulted from local sources of fine-grained material-perhaps volcanic eruptions.
Mars Orbiter Camera images are used to identify widespread material interpreted to have formed via explosive volcanism on Arsia Mons volcano, Mars. This material crops out in cliff sections associated with pit craters in layers ~45-50 m thick. The large range of elevations where the material is found (6.2-17.5 km) suggests locally-derived materials, although extensive reworking has produced a wide variety of dune forms. Two possible styles of volcanism appear possible for generating this material: (1) explosive volcanism associated with pit crater formation due to the release of magmatic gases, or (2) the interaction between dikes and volatile-rich substrates. Although the best examples occur on Arsia Mons, pit craters on Ascraeus Mons also suggest explosive activity. The absence of comparable features on Olympus Mons indicates that the eruptive histories of the larger Tharsis shields were more diverse than has been inferred from Viking Orbiter images.
The height reached by a volcanic eruption column, together with the atmospheric wind regime, controls the dispersal of tephra. Column height is itself a function of vent radius, gas exit velocity, gas content of eruption products, and efficiency of conversion of thermal energy contained in juvenile material to potential and kinetic energy during the entrainment of atmospheric air. Different heights will be attained for the same total energy release depending on the style of the eruption: a discrete explosion produces a transient plume, whereas a prolonged release of material forms a maintained plume. A maintained eruption plume will also be formed if discrete explosions occur within a few minutes of one another, and eruptions producing large volumes of tephra commonly lead to maintained plume formation. Observed eruption columns from eight eruptions with cloud heights in the range 2-45 km and volume rates of magma production in the range 10 to 2.3×105 m3/s are compared with predicted values deduced from theoretical relationships for fluid convection. Theoretical model model heights were calculated in two ways: first, for a wide range of eruptive conditions by using a dynamic model of eruption column formation and second, by using a theoretical formula relating height to rate of thermal energy release. Results from the two calculations were found to agree well and furthermore showed satisfactory agreement with the eight observations. Expected cloud heights can be usefully expressed as a function of heat release rate, expressed as the quivalent volume eruptions involve highly efficient use of the released heat, which indicates that the particle sizes in these eruptions are sufficiently small to allow rapid heat transfer to air entrained into the column. For certain combinations of vent radius, gas exit velocity, and gas content, column collapse to form pyroclastic flows should occur. Cloud heights have been calculated for a wide range of permutations of these parameters corresponding to the onset of collapse. The maximum theoretical height expected for a stable maintained plume is about 55 km, corresponding to a volume eruption rate of 1.1×106 m3/s.
Conditions required to support buoyant convective plumes are investigated for explosive volcanic eruptions from circular and linear vents on Earth, Venus, and Mars. Vent geometry (linear versus circular) plays a significant role in the ability of an explosive eruption to sustain a buoyant plume. On Earth, linear and circular vent eruptions are both capable of driving buoyant plumes to equivalent maximum rise heights; however, linear vent plumes are more sensitive to vent size. For analogous mass eruption rates, linear vent plumes surpass circular vent plumes in entrainment efficiency approximately when Lo >= 3ro owing to the larger entrainment area relative to the control volume. Relative to circular vents, linear vents on Venus favor column collapse and the formation of pyroclastic flows because the range of conditions required to establish and sustain buoyancy is narrow. When buoyancy can be sustained, however, maximum plume heights exceed those from circular vents. For current atmospheric conditions on Mars, linear vent eruptions are capable of injecting volcanic material slightly higher than analogous circular vent eruptions. However, both geometries are more likely to produce pyroclastic fountains, as opposed to convective plumes, owing to the low-density atmosphere. Because of the atmospheric density profile and water content on Earth, explosive eruptions enjoy favorable conditions for producing sustained buoyant columns, while pyroclastic flows would be relatively more prevalent on Venus and Mars. These results have implications for the injection and dispersal of particulates into the planetary atmosphere and the ability to interpret the geologic record of planetary volcanism.
The characteristics of the Madusae Fossae Formation suggest that it may represent equatorial deposition of ice-rich airborne dust during extended periods of high obliquity.
The recent flood lavas on Mars appear to have a characteristic "platy-ridged" surface morphology different from that inferred for most terrestrial continental flood basalt flows. The closest analog we have found is a portion of the 1783-1784 Laki lava flow in Iceland that has a surface that was broken up and transported on top of moving lava during major surges in the eruption rate. We suggest that a similar process formed the Martian flood lava surfaces and attempt to place constraints on the eruption parameters using thermal modeling. Our conclusions from this modeling are (1) in order to produce flows >1000 km long with flow thicknesses of a few tens of meters, the thermophysical properties of the lava should be similar to fluid basalt, and (2) the average eruption rates were probably of the order of 104 m3/s, with the flood-like surges having flow rates of the order of 105 - 106 m3/s. We also suggest that these high eruption rates should have formed huge volumes of pyroclastic deposits which may be preserved in the Medusae Fossae Formation, the radar "stealth" region, or even the polar layered terrains.
A new global model for the Martian atmosphere with a vertical domain extending from the surface into the thermosphere (at about 160–180 km) is presented with some preliminary results. The model is a grid point model with a semi-Lagrangian semi-implicit dynamical scheme that is used for weather forecasting by the Meteorological Service of Canada. The physics includes a comprehensive radiative transfer scheme for heating, a boundary and surface layer parameterization. The design of the model allows for different grid configurations that include a globally uniform grid as well as the possibility of zooming over an area of interest with a locally uniform grid. The performance of the model is shown both in global uniform-resolution simulations as well as high-resolution simulations over the Tharsis Montes region. The simulated temperatures are compared with the Thermal Emission Spectrometer's measured profiles and the Mars Pathfinder entry data. Both the agreement with the data and the depiction of known features of the Martian atmosphere indicate that the Global Mars Multiscale Model has a good potential for modeling the atmosphere of Mars.
Data from instruments on the currently orbiting Mars Global Surveyor (MGS) suggest that as an alternative interpretation to lacustrine deposits, widespread sediments on Mars may be tephra deposits of variable age, formed in part by volcano-ice interactions. The materials are often associated with outcrops of mapped geological units that have each been previously interpreted as volcanic ash deposits with identified, but unconfirmed possible volcanic vents. Spectral investigation indicates that although some outcrops are basaltic, many show moderate to high concentrations of andesite, a composition at which large explosive eruptions may be possible. In addition, many outcrops are in areas suspected to be water/ice rich. On Earth, magma and groundwater can react to create violent explosive eruptions. Observations from MGS support a pyroclastic mechanism of deposition and show some morphologies consistent with volcano-ice interactions, including subaqueous eruptions. Perhaps MGS data are finally producing more definitive evidence of the widespread tephra that were predicted to be likely in the reduced atmospheric pressure of Mars.
Eruption columns consist of two components. The lower gas thrust component results from decompression of the gas phase, and decelerates rapidly to near zero velocity at heights of 1.5–4.5 km for initial gas velocities of 400–600 m/s. The upper convective thrust component is due to the column having a lower density than the atmosphere, and can transport the column to heights of 30–40 km.
At the base, the effective density of a column is considerably greater than that of the atmosphere and is very sensitive to changes of gas content. Fall out of clasts and incorporation and heating of air reduce the density substantially during the gas thrust part. It is shown that columns formed from magmas with high water contents (5%) are likely to show convective motion. Magmas with low water contents ( 1 2 %) or high proportions of CO 2 will form a column with an effective density greater than the atmosphere, and gravitational column collapse can occur to generate ignimbrite-forming pyroclastic flows. In magmas with intermediate gas contents, the occurrence of convection (plinian case) or collapse (ignimbrite-forming) depends on vent radius, proportion of ash and gas content.
The model presented here can explain: the sharp transition from plinian to ignimbrite-forming activity; the increase of temperature with time shown by some ignimbrites; the common association of low temperature ignimbrites with preceding plinian eruptions, and the apparent mobility of pyroclastic flows.
Volcaniclastic sediments and rocks are divided here into autoclastic, pyroclastic, and epiclastic types with grain-size limits the same as non-volcanic epiclastic rocks. Autoclastic rocks contain fragments that are produced within (but not usually extruded from) volcanic vents, during movement of lava flows, or by gas explosions within flows that have ceased to flow. Pyroclastic rocks contain fragments produced by volcanic explosion and extruded as discrete particles from volcanic vents. Epiclastic volcanic rocks contain fragments produced by weathering and erosion of solidified or lithified volcanic rocks of any type. Volcaniclastic types may be mixed in all proportions with each other or with nonvolcanic fragments, although these mixtures are not designated within this classification. A non-genetic category, based only upon particle size and the presence of volcanic material, is included for rocks with clasts of unknown origin.
One of Earth's largest known eruptions, the Toba eruption of 75 ka, erupted a minimum of 2800 km3 of magma, of which at least 800 km3 was deposited as ash fall. This ash may be entirely of coignimbrite origin and dispersed widely because of high drag coefficients on the predominantly bubble-wall shards. Shards of this shape are broken from the walls of spherical vesicles, which formed in high abundance in isotropic strain shadows near phenocrysts in this crystal-rich magma.
High Resolution Stereo Camera (HRSC) images of Hadriaca Patera, Mars, in combination with Mars Orbiter Camera (MOC), Mars Orbiter Laser Altimeter (MOLA), and Thermal Infrared Imaging System (THEMIS) data sets, reveal morphologic details about this volcano and enable determination of a chronology of the major geologic events through new cratering age assessments. New topographic measurements of the Hadriaca edifice were also made from a HRSC-based high-resolution (125 m) digital terrain model (DTM) and compared to the MOLA DTM. We find evidence for a complex formation and erosional history at Hadriaca Patera, in which volcanic, fluvial, and aeolian processes were all involved. Crater counts and associated model ages suggest that Hadriaca Patera formed from early shield-building volcanic (likely explosive pyroclastic) eruptions at ~3.7-3.9 Ga, with caldera formation no later than ~3.5 Ga. A variety of geologic activity occurred in the caldera and on the northern flank and plains at ~3.3-3.5 Ga, likely including pyroclastic flows (that partially filled a large crater NW of the caldera, and plains to the NE) and differential erosion/deposition by aeolian and/or fluvial activity. There were some resurfacing event(s) in the caldera and on the eastern flank at ~2.4-2.6 Ga, in which the eastern flank's morphology is indicative of fluvial erosion. The most recent dateable geologic activity on Hadriaca Patera includes caldera resurfacing by some process (most likely differential aeolian erosion/deposition) in the Amazonian Period, as recent as ~1.5 Ga. This is coincident with the resurfacing of the heavily channeled south flank by fluvial erosion. Unlike the Tharsis shields, major geologic activity ended at Hadriaca Patera over a billion years ago.
Local and regional Mars Orbiter Laser Altimeter (MOLA) topographic data support the presence of an extensive Hesperian-aged volatile-rich south polar deposit (the Dorsa Argentea Formation, Hd, and related units) underlying the present Amazonian-aged polar cap (Api, residual ice, and Apl, layered terrain) and covering a surface area that could be as large as 2.94×106km2 (about 2% of the surface of Mars), over twice the area of the present Amazonian-aged south polar deposits. The deposit characteristics indicate that it contained significant quantities of water ice in amounts comparable to present-day polar deposits. Several lines of evidence for melting indicate that the ice sheet deposits underwent melt back and liquid water drainage into surrounding lows, including a large valley near the crater Schmidt and the Argyre basin. Narrow sinuous ridges lie in a broad linear depression extending from a high near the present polar cap continuously downslope to near the distal portion of Hd. The new topographic data support the interpretation of these ridges as eskers, representing meltwater distribution networks at the base of the receding deposit. Extensive development of large pits and depressions (cavi) have previously been interpreted as eolian etching or basal melting of ice-rich deposits. Analysis of MOLA topography supports the interpretation that they represent basal melting of ice-rich deposits and shows that they have links to the esker systems. Volumetric considerations and topographic lineations suggest that some of the basal melting occurred beneath regions presently occupied by Apl, and that some of the liquid water formed ponds and lakes in the distal parts of Hd. The presence of pedestal craters is further evidence of the removal of extensive volatile-rich deposits and contributes to the quantitative measure of the former deposit thickness. Where did the melt products go? Inspection of the margins of the Dorsa Argentea Formation reveals several large channels that begin there and drain downslope for distances between 900 and 1600 km onto the floor of the Argyre basin, some 3.5-4.0 km below their origin. These channels do not exhibit tributaries. Their broad lateral distribution supports other evidence that deposit melting was areally very widespread and volumetrically significant, and that a large part of the meltwater entered the surface distribution system and was deposited on the floor of the Argyre basin over 1000 km away. Estimates of the present deposit thicknesses together with amounts of the deposit removed by meltback suggest that the original volume could have been as much as 5.9×106km3, equivalent to a global layer of water ~20 m deep if the deposit consisted of~50% volatiles. A portion of these volatiles migrated across the surface to pond in adjacent valleys and basins, and into the groundwater system. A significant portion of the volatiles remain in the deposit, representing a net removal from the atmosphere and from the active hydrologic system in early to middle Mars history, and forming an accessible record of aqueous conditions and possible biological environments dating from that time.
We have used a combined conduit transport/eruption column model to explore the evolution of volcanic eruption plumes on Mars under different atmospheric conditions. In the calculations we consider a volatile phase composed of H2O, CO2, and SO2 and take into account that the magmatic water erupted at the vent may condense as the eruption column rises into the Martian atmosphere. As two end-member models, we explore the eruption of rhyolitic and basaltic melt compositions containing different amounts of volatiles as well as having different eruption temperatures. Under current Martian atmospheric conditions eruption plumes are found to rise as high as 100 km for a mass eruption rate of 5×107kgs-1, which is consistent with model calculations by Wilson and Head [1994]. In contrast, under a dense atmosphere (105Pa on the Martian surface) which may have existed earlier in Martian history, the same eruption plume reaches only about 25 km height. All magmatic water released during the eruption is found to freeze as it rises in the eruption column, which means that fallout from the plume will contain water ice which can be subsequently deposited in near surface layers. This ice may then suddenly melt due to higher surface heat flow or shallow intrusions leading to rapid release of water on the flanks of volcanoes. Only if the atmosphere were hotter in the past could the water in the eruption plume condense and produce rain rather than ice. Furthermore, the calculations show that smaller micron-size particles would be distributed globally from eruption plumes under current Martian conditions but would not have been as widely dispersed from plumes erupted into an earlier dense atmosphere.
Yardangs are streamlined erosional wind forms, similar in form to inverted boat hulls, that in terrestrial deserts range from meters to kilometers in length. On Mars the best examples are seen in the equatorial region. In the Amazonis region, hundreds of ridges and sawtooth-edged mesas have been wind sculptured in layered rocks. Individual ridges are tens of kilometers long with intervening valleys nearly 1 km wide. The wind-stripped surface seems to be relatively young and therefore must be easily erodible. Possible lithologies include ignimbrites, mudflows, or lithified regolith. Other wind-sculpted features occur in the Aeolis region, in Ares Valles, and in the Iapygia region. White Rock, a light-colored plateau inside a crater, is interpreted to be a yardang cluster eroded in a deposit inside the host crater. White Rock may be a jointed, wind-eroded pyroclastic deposit. Yardangs on Mars, especially when they are sculpted in young geologic units, demonstrate that much of the observed eolian erosion is recent. Yardang azimuths often are not parallel with wind streak directions, indicating that the yardangs were formed by different (older or weaker) winds from those that formed the streaks.
Theories of convection from maintained and instantaneous sources of buoyancy are developed, using methods which are applicable to stratified body fluids with any variation of density with height; detailed solutions have been presented for the case of a stably stratified fluid with a linear density gradient. The three main assumptions involved are (i) that the profiles of vertical velocity and buoyancy are similar at all heights, (ii) that the rate of entrainment of fluid at any height is proportional to a characteristic velocity at that height, and (iii) that the fluids are incompressible and do not change volume on mixing, and that local variations in density throughout the motion are small compared to some reference density. The governing equations are derived in non-dimensional form from the conditions of conservation of volume, momentum and buoyancy, and a numerical solution is obtained for the case of the maintained source. This leads to a prediction of the final height to which a plume of light fluid will rise in a stably stratified fluid. Estimates of the constant governing the rate of entrainment are made by comparing the theory with some previous results in uniform fluids, and with the results of new experiments carried out in a stratified salt solution. For the case of an instantaneous source of buoyancy there is an exact solution; the entrainment constant is again estimated from laboratory results for a stratified fluid. Finally, the analysis is applied to the (compressible) atmosphere, by making the customary substitution of potential temperature for temperature. Predictions are made of the height to which smoke plumes from typical sources of heat should rise in a still, stably stratified atmosphere under various conditions.
This study proceeds to examine aspects of importance, or possible importance, to meteorology-principally the dust veils created in the atmosphere, particle sizes and distribution, heights, fall speeds and atmospheric residence times. Later sections deal with spread of the dust by the atmospheric circulation and the direct effects apparent upon radiation, surface temperature and extent of ice in the polar regions. These effects, as well as various crude measures of the total quantity of solid matter thrown up, are used to arrive at numerical assessments of volcanic eruptions in terms of a dust viel index (DVI), The appendices give a chronology of eruptions and a chronology of DVI values.
A model for absorption by the CO2 15-microns band has been adapted from the Morcrette et al. (1986) terrestrial wide-band model for use in a general circulation model of the Martian atmosphere. The absorption model is validated by comparison with exact line-by-line integrations for a set of atmospheric profiles characteristic of Martian conditions. The Doppler effect is included in a simple way with no significant increase of the computational cost. The model gives accurate results up to 80 km. The Doppler effect, in fact, is shown to be significant only above 50 km for mean Martian conditions. The transmissivities of the wide-band model are fitted to the results of a more accurate statistical narrow-band model. Various formulations of the statistical band model, including accurate representation of the Doppler effect (Fels, 1979; Zhu, 1989) are validated by comparison with line-by-line results.
Different lines of evidence point to hydrological cycling in the martian past. The extent, duration, and magnitude of this cycling remains unclear, as well as the magnitude of aqueous processes on the surface. Here, we provide geomorphic and mineralogic evidence of a large inter-crater sedimentary basin located in the Terra Sirenum region, which was once covered by a body of liquid water with an areal extent of at least 30,000km2 and a depth of approximately 200m. The topographic basin, which is modified by a number of large impact craters, is partly controlled by ancient impact and tectonic structures. As a result of evaporation of the large body of water, salt flats formed in the lowest topographic reaches of the basin. Hydrated phyllosilicates occur in close proximity to the salt flats and in the ejecta and rim materials of small impact craters with stratigraphic relations that suggest that they underlie the evaporite deposits. Crater statistics place the maximum age of aqueous activity during the Late Noachian epoch. The relatively pristine mineral deposits in the basin have a high potential to yield information of the geochemistry and water activity during the ancient Noachian Period when conditions were seemingly more conducive to life.
Here is presented a general description of the Atlantis Basin geology, where the existence of different geological features seem to indicate the long-term presence of a thermal source and a water reservoir stable enaough to sustain biological processes.
A planetary global circulation model developed by the Laboratoire de Météorologie Dynamique (LMD) was used to simulate explosive eruptions of ancient martian volcanoes into paleo-atmospheres with higher atmospheric pressures than that of present-day Mars. Atmospheric pressures in the model were varied between 50 mbar and 2 bars. In this way it was possible to investigate the sensitivity of the volcanic plume dispersal model to atmospheric pressure. It was determined that the model has a sensitivity to pressure that is similar to its sensitivity to other atmospheric parameters such as planetary obliquity and season of eruption. Higher pressure atmospheres allow volcanic plumes to convect to higher levels, meaning that volcanic pyroclasts have further to fall through the atmosphere. Changes in atmospheric circulation due to pressure cause pyroclasts to be dispersed in narrower latitudinal bands compared with pyroclasts in a modern atmosphere. Atmospheric winds are generally slower under higher pressure regimes; however, the final distance traveled by the pyroclasts depends greatly on the location of the volcano and can either increase or decrease with pressure. The directionality of the pyroclast transport, however, remains dominantly east or west along lines of latitude. Augmentation of the atmospheric pressure improves the fit between possible ash sources Arsia and Pavonis Mons and the Medusae Fossae Formation, a hypothesized ash deposit.
Observations have been made using the combined VLA/Goldstone radar
instrument at 3.5-cm. This technique has provided the first unambiguous
radar cross section maps of Mars and Mercury at any wavelength. The most
interesting structures probed by us on Mercury were features near and
including the north and south poles. The polarization characteristics
and signal strength indicate that ices exist in some quantity in the
polar regions of Mercury. These ices probably exist in permanently
shaded areas at high latitudes. We also found several large,
quasi-circular regions on the surface of Mercury which have anomalously
high radar cross sections. The Caloris basin shows no such anomaly,
indicating that these large structures are probably not large impact
basins. Our Mars experiments were the first to identify an unusually
high cross section feature at the south pole, which is undoubtedly due
to the ice of the residual cap. There is no such feature at the north
pole, which we think is caused by some combination of three effects: (1)
a fundamental difference in the structure and/or composition of the two
residual caps, (2) the seasonal CO2 cap which was present during the
north polar experiments absorbed enough of the incoming radar energy to
obscure the north residual cap, and (3) the north polar regions were
imaged with slightly poorer geometry. Many other regions with anomalous
cross sections were found on the surface of Mars. The large volcanic
provinces of Tharsis and Elysium have very high cross sections
associated with them. These are most probably a result of the extremely
rough surfaces of the large volcanoes and their associated flows. One of
the most intriguing features in the Mars data set is a region which
extends west from Tharsis for over 2000 km. This region displays no
detectable cross section, prompting us to name it 'Stealth'. The surface
and near surface must be composed of very underdense material, with an
absence of volume scatterers (rocks). The proximity of Stealth to
Tharsis suggests that it may be comprised in part of pyroclastic
materials which were blown westward after eruptions from the large
shield volcanoes.
Introduction: Abundant geological evidence, both chemical and morphological, now exists for the presence of liquid water on Mars in the Noachian and Hesperian eras. Where did this water come from? Was it the consequence of an early climate that was warmer over an extended period, or of episodic, possibly catastrophic events? If the climate was warmer, what was the cause, given that the young Sun was around 25 % weaker at this time? To address these long-standing questions, we have performed three-dimensional simulations of Mars with a denser CO 2 atmosphere, as is believed to have existed in the Noachian era. We have investigated the Martian climate and water cycle under a faint young Sun for a range of atmospheric pressures, in order to better understand the possible conditions in this era. We are particularly interested in a) investigating if a steady-state warm, wet early Martian climate is possible b) determining the conditions that lead to significant precipitation (rain or snow) over the equatorial valley networks, and c) assessing the plausibility of an ancient northern ocean.
Aeolian features observed on the surface of Mars provide insight into current, and potentially past, surface wind systems. In some cases the features are clearly transient and related to the lifting and settling of atmospheric dust. Other features, like dunefields, yardangs, and ventifacts, are more persistent and likely require significant time to form. In this study we analyze the observed directions of selected aeolian features with the aid of the Geophysical Fluid Dynamics Laboratory Mars general circulation model (GCM). Initially, we examine bright and dark streaks which have been observed to form in association with global dust storms. The ability to mtch these features with Mars GCM wind directions provides an important validation of the model. More important, we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the Veverka et al [1981] model of bright and dark dust streak formation. In addition these best fit times correspond well with the dark streak "wind storm" model of Magalhaes and Young [1995]. The primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long-term wind indicators (for example, the misalignment of rock tail and ventifact orientations at the Mars Pathfinder landing site). Specifically, we assess whether changes in planetary obliquity, precession, or global dust opacity could significantly alter patterns of surface wind directions. In all cases we find the seasonal and annual average wind direction patterns to be highly invariable. While changes in the dust loading (hence the partitioning of solar absorption between the surface and atmosphere) and in the surface latitude of maximum solstitial insolation cause the vigor of the large-scale circulation to increase (especially the Hadley cell), the spatial patterns of the surface wind orientations remain essentially unchanged. In the case of perihelion during northern summer (opposite of the current perihelion position), the northern summer Hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere. Taken together, these results cast significant doubt on orbital explanations for surface wind changes. It is thus suggested that significant changes in topography (e.g., Tharsis uplift, true polar wander) or climate (e.g., the existence of a significantly thicker atmosphere or an ocean at some point in the past) are more likely explanations for long-term wind indicators such as the ventifact orientations at the Mars Pathfinder landing site.