No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Mass movement slope streaks imaged by the Mars Orbiter Camera
Journal of Geophysical Research: Planets
Abstract
Narrow, fan-shaped dark streaks on steep Martian slopes were originally observed in Viking Orbiter images, but a definitive explanation was not possible because of resolution limitations. Pictures acquired by the Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) spacecraft show innumerable examples of dark slope streaks distributed widely, but not uniformly, across the brighter equatorial regions, as well as individual details of these features that were not visible in Viking Orbiter data. Dark slope streaks (as well as much rarer bright slope streaks) represent one of the most widespread and easily recognized styles of mass movement currently affecting the Martian surface. New dark streaks have formed since Viking and even during the MGS mission, confirming earlier suppositions that higher contrast dark streaks are younger, and fade (brighten) with time. The darkest slope streaks represent ∼10% contrast with surrounding slope materials. No small outcrops supplying dark material (or bright material, for bright streaks) have been found at streak apexes. Digitate downslope ends indicate slope streak formation involves a ground-hugging flow subject to deflection by minor topographic obstacles. The model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits. This process is analogous to terrestrial avalanches of oversteepened dry, loose snow which produce shallow avalanche scars with similar morphologies. Low angles of internal friction typically 10–30¡ for terrestrial loess and clay materials suggest that mass movement of (low-cohesion) Martian dusty air fall is possible on a wide range of gradients. Martian gravity, presumed low density of the air fall deposits, and thin (unresolved by MOC) failed layer depths imply extremely low cohesive strength at time of failure, consistent with expectations for an air fall deposit of dust particles. As speed increases during a dust avalanche, a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension, limiting the momentum of the descending avalanche front. The equilibrium speed, where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends, decreases with decreasing gradient. This mechanism explains observations from MOC images indicating slope streaks formed with little reserve kinetic energy for run-outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends. The mass movement process of dark (and bright) slope streak formation through dust avalanches involves renewable sources of dust only, leaving underlying slope materials unaffected. Areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating, not just residing.
... Slope streaks represent one of the most widespread active geological processes on the present-day surface of Mars (e.g., Sullivan et al., 2001). Orbital images from several missions showed that these tens to hundreds of meters scale gravity-driven landforms occur throughout the martian year on dust-rich equatorial slopes (Sullivan et al., 2001;Schorghofer and King, 2011). ...
... Slope streaks represent one of the most widespread active geological processes on the present-day surface of Mars (e.g., Sullivan et al., 2001). Orbital images from several missions showed that these tens to hundreds of meters scale gravity-driven landforms occur throughout the martian year on dust-rich equatorial slopes (Sullivan et al., 2001;Schorghofer and King, 2011). Newly formed dark streaks have a high contrast and well-defined boundaries to the surrounding surfaces (Sullivan et al., 2001). ...
... Orbital images from several missions showed that these tens to hundreds of meters scale gravity-driven landforms occur throughout the martian year on dust-rich equatorial slopes (Sullivan et al., 2001;Schorghofer and King, 2011). Newly formed dark streaks have a high contrast and well-defined boundaries to the surrounding surfaces (Sullivan et al., 2001). The repeated imaging of slope streaks in various regions revealed that the streaks brighten with time, sometimes become brighter than their surroundings (e.g., Sullivan et al., 2001;Valantinas et al., 2021) and fade away due to settling dust from the atmosphere in time scales from months to decades (e.g., Baratoux et al., 2006;Bergonio et al., 2013;Dundas, 2020;Primm et al., 2020). ...
... From orbital images, we identified dust avalanches (also known as slope streaks) in this region (orange symbols on Fig. 1). These are known active mass wasting processes occurring on Mars in several contexts (Ferguson and Lucchitta, 1984;Sullivan et al., 2001;Aharonson et al., 2003;Schorghofer et al., 2002Schorghofer et al., , 2007Schorghofer and King, 2011;Gerstell et al., 2004;Baratoux et al., 2006;Chuang et al., 2007;Bergonio et al., 2013;Heyer et al., 2019Heyer et al., , 2020Valantinas et al., 2021). They appear as relatively dark or bright streaks on steep dustcovered slopes and occur in regions with a high albedo and low to very low thermal inertia (Sullivan et al., 2001;Aharonson et al., 2003). ...
... These are known active mass wasting processes occurring on Mars in several contexts (Ferguson and Lucchitta, 1984;Sullivan et al., 2001;Aharonson et al., 2003;Schorghofer et al., 2002Schorghofer et al., , 2007Schorghofer and King, 2011;Gerstell et al., 2004;Baratoux et al., 2006;Chuang et al., 2007;Bergonio et al., 2013;Heyer et al., 2019Heyer et al., , 2020Valantinas et al., 2021). They appear as relatively dark or bright streaks on steep dustcovered slopes and occur in regions with a high albedo and low to very low thermal inertia (Sullivan et al., 2001;Aharonson et al., 2003). Dust avalanches on Mars typically appear darker than the surrounding terrain. ...
... Text S1 for details on the imagery processing and mapping). The older observations, provided by both MOC and THEMIS-Vis, were only used for confirming the very low fading rate (Sullivan et al., 2001), being in good agreement with the dust activity reported in this region (Battalio and Wang, 2021). ...
... Slope streaks são feições escuras e lineares encontradas nas regiões equatoriais de Marte. Elas se destacam por sua baixa reflectância e aspecto alongado (Figura 1), surgindo em regiões com altas concentrações de poeira, baixa inércia térmica e alto albedo, como documentado por diversos autores (Ferguson e Lucchitta, 1984;Williams, 1991;Sullivan et al., 2001;Schorghofer et al., 2002;Kreslavsky e Head, 2009;Brusnikin et al., 2015). ...
... A descoberta inicial dessas feições ocorreu em imagens da missão Viking na década de 1970, destacando a importância das contribuições de Morris (1982) e Ferguson e Lucchitta (1984) nesse campo. Elas surgem de maneira súbita nas encostas durante os períodos quentes marcianos e, ao longo do tempo, gradualmente desaparecem, como apontado por Sullivan et al. (2001). A abundância dessas marcas as colocam como uma das formas mais significativas de movimento de massa em Marte, conforme discutido por Phillips et al. (2007). ...
... Estes rastros, ainda de natureza desconhecida, são encontrados em encostas inclinadas com baixa inércia térmica e experimentam temperaturas que atingem pelo menos 0°C uma vez por ano, conforme documentado por Schorgofer et al. (2002). Elas se manifestam como marcas alongadas, frequentemente mais escuras do que as áreas circundantes, embora variações mais claras também ocorram, sendo referidas como bright slope streaks (Sullivan et al., 2001). (NASA, 2005). ...
Slope streaks are dark and elongated features on Mars that form rapidly on the Martian surface. They are associated with areas of low
thermal inertia and regions with high albedo. These streaks gradually lighten over the years. Understanding their formation is crucial
for comprehending environmental factors on Mars. This study aims to create a database of HiRISE images containing slope streaks.
This database was constructed from a density map of images taken by the HiRISE camera aboard the Mars Reconnaissance Orbiter
(MRO). The Kernel density map gathered 217 scenes from 84,772 images from the Planetary Imagery Research Laboratory, and it
aligns with global distributions reported in the literature. This enables researchers to locate specific scenes with customized filters and
access detailed information about the HiRISE images. The included observation dates allow for tracking the evolution of slope streaks
over time, identifying trends and seasonal patterns. In summary, this study deepens our understanding of slope streaks on Mars and
provides a valuable tool for ongoing research into these unique geological features on the Martian surface.
... We divide slope streak formation hypotheses into two general categories: dry and wet. The dry hypothesis states that slope streaks are formed by the granular flow of dry material on steep slopes exposing a lower-albedo material (Sullivan et al. 2001; Baratoux et al. 2006;Chuang et al. 2007Chuang et al. , 2010Phillips et al. 2007). Slope streaks are commonly found in highly dustcovered areas on Mars, which supports formation by dry dust avalanches (Schorghofer et al. 2002), and impacts have been shown to trigger slope streak formation (Burleigh et al. 2012). ...
... Although there is no apparent accumulation of material at the toe, as might be expected for dry flows, Dundas (2020) finds geomorphologic features consistent with low-density avalanches of dry surface material in new slope streaks. It is unclear how the variable fading rate and albedo changes fit into the dry hypothesis because some slope streaks fade quickly, others appear to remain dark for decades, and some old streaks fade but leave a brighter deposit behind (Sullivan et al. 2001). ...
... A global study comparing slope streak location to Gamma Ray Spectrometer data also found a correlation between slope streak occurrence and regions of increased iron at a global scale (Bhardwaj et al. 2017). A geographic distribution associated with dust-mantled regions was previously noted (Sullivan et al. 2001). In addition to the relationship with iron abundance, Bhardwaj et al. (2017) argued that slope streak location is correlated with atmospheric water and chlorine abundance and suggested a salty brine formation mechanism because chlorine salts are hygroscopic and could form brines when exposed to elevated levels of atmospheric water. ...
Martian slope streaks are large surface features with lower albedo than their surroundings that are one of the few active geologic processes occurring on Mars today. We investigated the slope streaks’ spectral properties using images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at nine sites, including three sites with observations over multiple years to enable time-series analysis. For each individual slope streak within each image, we determined the average spectra of each streak and of the slope immediately adjacent to account for changes in geology across a CRISM image or within slopes containing streaks. We find a trend where the visible spectral continuum (0.4–0.6 μ m) is strongly negative for the darkest slope streaks, and the spectral continuum increases as the slope streaks fade, consistent across all sites and over multiple observations of the same site. We do not find absorption at 1.4 or 1.9 μ m associated with hydration. In some slope streaks, we see evidence of Fe-bearing minerals, but these signatures are also found in the streak-free slope directly adjacent, suggesting that the streaks have a similar mineralogy to their surroundings. The spectral changes that we see are most consistent with changes in the fine dust component and support a dry flow mechanism whereby slope streaks are formed by processes that trigger dust removal from the slope in particular locations, with the streaks slowly fading as dust resettles on the surface.
... Slope streaks are dark tracks that suddenly appear on the slopes of low-latitude regions on Mars. These streaks gradually become lighter until they become indistinct on the surface (Sullivan et al., 2001). The features were initially identified in images from the Viking mission by Morris (1982), Ferguson and Lucchitta (1984), and their abundance makes them one of the most significant forms of mass movement on the planet (Phillips et al., 2007). ...
... Streak sizes vary significantly, characterized by a high length-to-width ratio. While the length of the features can range from a few meters to thousands of meters, their respective ratio varies between 5 and 30, rarely exceeding 50 (Sullivan et al., 2001). ...
... The texture of the streaks is influenced by the surrounding terrain and can be divided into apical, medium, and basal sections (Sullivan et al., 2001). Currently, all models consider peaks as the starting points for streak formation (e.g., Ferguson and Lucchitta, 1984;Williams, 1991;Sullivan et al., 2001;Schorghofer et al., 2002;Kreslavsky and Head, 2009). ...
Slope streaks are dark features found in low-latitude regions of Mars, formed from rapid-duration events in low thermal inertia terrain. The sudden appearance of low reflectance factor (I/F) patches followed by gradual whitening is a planet-relevant environmental indicator. The present work aims to quantify the variation in the fading of slope streaks using HiRISE/MRO images. We carried that out by analyzing I/F contrast of 31 streaks about their surroundings north of Olympus Mount, arranged in 16 images dated from 2007 to 2021, used as a dataset for measuring the formation and brightening of the streaks in the region. For the contrast calculations, we used I/F data points extracted from within the streaks and their brighter surroundings. We conducted a statistical analysis on the contrast distribution of each slope streak to test for normality and homogeneity of variances. Using Welch's t-Test, we found that the average albedo contrast values of the slope streaks were statistically different across all pairwise comparisons between dates. Our study provides some insight on the contrast variation (due to sediment deposition) of the streaks along time and seasonal correlation. The results point out to a possible dry formation process, such as dust avalanches, but are not sufficient to rule out wet mechanisms.
... The Martian crust is known to be rich in iron, which exists in both ferric (Fe 3+ ) and ferrous (Fe 2+ ) bearing mineral phases. Typical dust removal processes, such as dust devils (e.g., Thomas and Gierasch, 1985;Balme and Greeley, 2006), and slope streaks (e.g., Sullivan et al., 2001;Dundas, 2020) tend to expose the generally less oxidized ferrous surface material. The width of the spectral responses of CaSSIS over the 400 to 1100 nm range allows us to effectively discriminate between these ferrous and ferric bearing surfaces based on their characteristic electronic absorptions near 1000 nm and 550 nm, respectively ( Fig. 1). ...
... Slope streaks are narrow, linear features typically found on dustcovered steep slopes in low thermal inertia regions near the Martian equator (Sullivan et al., 2001;Chuang et al., 2010;Putzig et al., 2005) and were first identified in Viking orbiter images (Morris, 1982). Subsequently, availability of higher resolution datasets like the MOC, HiRISE and now CaSSIS have facilitated both global (Sullivan et al., 2001;Aharonson et al., 2003;Schorghofer et al., 2007;Dundas, 2020) and regional scale studies (Chuang et al., 2007;Phillips et al., 2007;Schorghofer and King, 2011;Bergonio et al., 2013) to better understand the origin and evolution of these features over time. ...
... Slope streaks are narrow, linear features typically found on dustcovered steep slopes in low thermal inertia regions near the Martian equator (Sullivan et al., 2001;Chuang et al., 2010;Putzig et al., 2005) and were first identified in Viking orbiter images (Morris, 1982). Subsequently, availability of higher resolution datasets like the MOC, HiRISE and now CaSSIS have facilitated both global (Sullivan et al., 2001;Aharonson et al., 2003;Schorghofer et al., 2007;Dundas, 2020) and regional scale studies (Chuang et al., 2007;Phillips et al., 2007;Schorghofer and King, 2011;Bergonio et al., 2013) to better understand the origin and evolution of these features over time. Newer streaks usually appear darker, possess lower brightness values and have stronger contrast compared to the surrounding terrain (Schorghofer et al., 2007;Valantinas et al., 2021), and can form all year round, with greater concentrations observed in local autumn (Heyer et al., 2019;Dundas et al., 2021). ...
Mars is host to a variety of active surface processes that relate to changes in seasonal ice/frost, slope activity, wind and processes potentially relating to liquid water. Regular monitoring and change detection of these phenomena is crucial to not only provide us insights into present day Martian surface conditions, but also its past geologic and climatic scenarios. Visual comparisons of high-resolution remote sensing images of the surface from the Mars Reconnaissance Orbiter (MRO) have allowed detailed tracking and monitoring of these changes over time. The CaSSIS instrument onboard the ExoMars Trace Gas orbiter also provides a unique pathway to track areally-large surface changes in colour, that permits us to better constrain origin and evolution of various surface features. Since TGO operates in a non-sun-synchronous orbit, previously adopted qualitative methods like visual image comparisons for MRO cannot be adopted for CaSSIS-based change detection. Consequently, this study lists and describes in detail, the techniques that need to be adopted to conduct such change detection campaigns with CaSSIS, for the variety of active processes currently identified on Mars. This work also proposes and describes two additional semi-quantitative techniques for CaSSIS-based change detection, that may be used in concert with existing visual comparison methods to enable reliable change identification and tracking. It is observed that these supplementary methods work well in characterizing a variety of surface changes related to ice/frost and slope processes, and can provide reasonable spectral constraints to better understand their origin. These methods are not effective in providing quantitative constraints for purely physical changes. Instead, for long-period changes like aeolian bedform movement, digital image correlation techniques on ortho-rectified images, are recom- mended; while for short period changes like real-time dust devil activity, measurements based on CaSSIS stereo pairs of the region can be used to provide quantitative estimates of change.
... Rastros em encostas na superfície de Marte são faixas alongadas, tipicamente mais escuras que suas áreas circundantes e se estendem sobre declives íngremes (SULLIVAN et al., 2001), como mostram os exemplos da Fig. 1. Estes rastros representam um processo geológico que ocorre, sob as atuais condições climáticas, na superfície do planeta vermelho. ...
... Os primeiros rastros em encostas marcianos foram observados por Morris (1982) e Ferguson e Lucchitta (1984) em imagens com resolução espacial de aproximadamente 100 m de resolução obtidas pelas sondas Viking Orbiters. Posteriormente, foram observados mais detalhadamente por Malin e Edgett (2001) e Sullivan et al. (2001) através de imagens adquiridas pela câmera MOC (Mars Orbiter Camera), com resolução espacial de até 1,5 m. Em agosto de 2005, as câmeras HiRISE (High Resolution Imaging Science Experiment) e CTX (Context Camera) foram enviadas a Marte, e com imagens cuja resolução espacial é de até 0,25 m e 6 m, respectivamente, ambas têm registrado a presença de rastros em encostas desde então (McEWEN et al., 2007). ...
... Os rastros são tipicamente mais escuros que a área circundante, todavia, em raras ocorrências, foram encontrados rastros mais claros à região de vizinhança. Estudos realizados por Sullivan et al. (2001) sugerem que existe relação entre o albedo e a idade de exposição. Rastros formados mais recentemente são mais escuros que os outros da mesma região, e vão clareando com os anos. ...
Este trabalho apresenta uma metodologia para segmentação automática de rastros em encostas em imagens da superfície de Marte. Rastros em encostas são faixas escuras que se estendem por declives íngremes do planeta vermelho. Estes rastros representam um dos poucos processos geológicos ativos na superfície marciana. Embora exista um número considerável de pesquisadores que os estudam, a identiï¬cação destes ainda é realizada por especialistas de forma manual, através de amostras de pequena dimensão. A disponibilidade de uma metodologia para segmentar e extrair informações signiï¬cativas aumenta naturalmente o conhecimento e a signiï¬cância estatística dos dados estudados, uma vez que uma quantidade muito maior de imagens em diferentes locais pode ser analisada. Desta forma, a proposta deste trabalho consiste em apresentar uma metodologia para segmentação automática de rastros em encostas em imagens Context Camera (CTX) da superfície de Marte, visando contribuir dessa forma, para a automação do processo de extração de informações a respeito do fenômeno em questão. A metodologia desenvolvida baseia-se principalmente em operadores morfológicos e ï¬ltro de fator de forma. Através da avaliação do desempenho por métricas baseadas em pixel, constatou-se que a metodologia mostrou-se eï¬ciente com a taxa de acertos de 80% e pode ser utilizada para dar início ao levantamento, em larga escala, de rastros em encosta em Marte.
... Slope streaks are dark wedge-shaped surface features on sloped terrains associated with downslope mass movement (Chuang et al., 2007;C. Phillips et al., 2007;Ferris et al., 2002;Kreslavsky & Head, 2009;Miyamoto et al., 2004;Schorghofer et al., 2002Schorghofer et al., , 2007Sullivan et al., 2001) that form exclusively in dusty low thermal inertia terrains. The initiating and sustaining mechanisms of slope streaks have been attributed to wet (Kreslavsky & Head, 2009;Mushkin et al., 2010;Schorghofer et al., 2002) or dry processes (Baratoux et al., 2006;Burleigh et al., 2012;Chuang et al., 2007Chuang et al., , 2010C. ...
... The initiating and sustaining mechanisms of slope streaks have been attributed to wet (Kreslavsky & Head, 2009;Mushkin et al., 2010;Schorghofer et al., 2002) or dry processes (Baratoux et al., 2006;Burleigh et al., 2012;Chuang et al., 2007Chuang et al., , 2010C. Phillips et al., 2007;Dundas, 2020;Schorghofer et al., 2002;Sullivan et al., 2001), without conclusive evidence one way or the other (Bhardwaj et al., 2019;Dundas, 2020). The longer-than-expected character of slope streaks on shallow Martian slopes requires some form of lubricating agent that has led Piqueux et al. (2016) to propose a connection with diurnal CO 2 ice sublimation grain motions and slope destabilization. ...
... Slope streaks (Figure 8) are dark wedge-shaped surface features on sloped terrains, initiating at a point and broadening downslope (Chuang et al., 2007;C. Phillips et al., 2007;Ferris et al., 2002;Kreslavsky & Head, 2009;Miyamoto et al., 2004;Schorghofer et al., 2002;Sullivan et al., 2001). Work by Chuang et al. (2007) also shows that slope streaks are associated with mass movement downslope and are not limited to a simple darkening of the surface. ...
Before dawn on the dustiest regions of Mars, surfaces measured at or below ∼148 K are common. Thermodynamics principles indicate that these terrains must be associated with the presence of CO2 frost, yet visible wavelength imagery does not display any ice signature. We interpret this systematic absence as an indication of CO2 crystal growth within the surficial regolith, not on top of it, forming hard‐to‐distinguish intimate mixtures of frost and dust, that is, dirty frost. This particular ice/regolith relationship unique to the low thermal inertia regions is enabled by the large difference in size between individual dust grains and the peak thermal emission wavelength of any material nearing 148 K (1–2 μm vs. 18 μm), allowing radiative loss (and therefore ice formation) to occur deep within the pores of the ground, below several layers of grains. After sunrise, sublimation‐driven winds promoted by direct insolation and conduction create an upward drag within the surficial regolith that can be comparable in strength to gravity and friction forces combined. This drag displaces individual grains, possibly preventing their agglomeration, induration, and compaction, and can potentially initiate or sustain downslope mass movement, such as slope streaks. If confirmed, this hypothesis introduces a new form of CO2‐driven geomorphological activity occurring near the equator on Mars and explains how large units of mobile dust are currently maintained at the surface in an otherwise soil‐encrusting world.
... Linear and fan-shaped albedo features, known as dark slope streaks, were discovered in Viking orbiter images of the Olympus Mons aureole (Morris, 1982). Knowledge about their global extent and formation mechanism was considerably expanded using the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC; Malin and Edgett, 2001) datasets (Sullivan et al., 2001;Schorghofer et al., 2007). Very high image resolution (~0.3 m/px) analysis studies based on the Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Experiment (HiRISE;McEwen et al., 2007) revealed further information about slope streak morphology and aeolian surface evolution (e.g. ...
... Within the forty years of orbital observations of slope streaks several hypotheses have been raised to explain their origin. Initially proposed to be debris weathered from dark pyroclastic materials (Morris, 1982), a dry model where avalanching surface dust exposes a deeper, darker, and presumably less oxidized Martian substrate was subsequently suggested (Williams, 1991;Sullivan et al., 2001;Dundas, 2020b). The latter model was supported by low-sun illumination HiRISE observations, which showed that a surface layer is removed, at least in large slope streaks (Phillips et al., 2007;Chuang et al., 2007). ...
... Slope streaks are known to be darker than their surrounding material by~10% (Sullivan et al., 2001). The various contrast states of slope streak darkness suggested that a time-dependent fading mechanism likely related to dust deposition is occurring (Aharonson et al., 2003). ...
Slope streaks are albedo features that form frequently on equatorial Martian slopes. Most slope streaks are dark relative to surrounding terrains, a minor fraction is bright, and there are rare transitioning streaks that exhibit a contrast reversal partway downslope. Their formation mechanisms and physical surface properties are not well understood. New observations acquired by the Colour and Stereo Surface Imaging System (CaSSIS) on board ESA's ExoMars Trace Gas Orbiter (TGO) provide insights into slope streaks' surface microstructure, roughness and particle size ranges. Using multiple phase angle observations, we show that dark slope streaks are substantially rougher and possibly more porous than their bright counterparts, which are likely composed of more compact regolith. Color data acquired in the four wavelength bands suggest that dark streaks are spectrally similar to bright streaks but are composed of larger particles. The comparison of our orbital results to the laboratory measurements of Martian regolith analogs indicates that particles within dark slope streaks may be up to a factor of four larger than the granular material of the surrounding terrains. At one study site in Arabia Terra, using complementary imagery from other orbiters, we identify a case where dark slope streaks turned fully bright in a twenty-year period. These and CaSSIS observations suggest that bright slope streaks are old dark slope streaks, likely formed by deposition of dust or decomposition of surface aggregates into smaller particles.
... A variety of activity occurs in gullies, but in general, the landforms are created by many individual flow events. This contrasts with slope streaks (e.g., Sullivan et al., 2001) and recurring slope lineae (RSL; McEwen et al., 2011), which are relatively superficial features with little resolved topographic effect, although the latter often occur within small gully landforms and may contribute to their incision. Gully activity also differs from the formation of dune alcoves discussed in Section 5, which are larger than standard slipface grainflow source areas but smaller than the alcoves at the head of dune gullies, and which are commonly found in the north polar dunes and form in one event Hansen et al., 2011). ...
... New slope streaks were first observed in MOC images, and it was quickly noted that the new streaks were always darker than existing streaks, indicating that they fade over time (Sullivan et al., 2001). Aharonson et al. (2003) conducted a survey of 173 collocated image pairs and found that the rate of formation of new streaks was ∼7% per existing streak, per Martian year, and apparently exceeded the rate of streak fading. ...
... Individual streaks form rapidly, within days (Dundas et al., 2017;Heyer et al., 2018) and possibly much faster, and then do not evolve further other than fading slowly. Existing streaks can prevent propagation of new streaks, but overprinting does occur occasionally (Dundas, 2020b;Sullivan et al., 2001). The seasonality of slope streak formation has been debated. ...
Mars exhibits diverse surface changes at all latitudes and all seasons. Active processes include impact cratering, aeolian sand and dust transport, a variety of slope processes, changes in polar ices, and diverse effects of seasonal CO2 frost. The extent of surface change has been surprising and indicates that the present climate is capable of reshaping the surface. Activity has important implications for the Amazonian history of Mars: understanding processes is a necessary step before we can understand their implications and variations over time.
... fall tracks/bounces (Chuang et al., 2007;Yakovlev et al., 2020). Slope streaks are thought to result from a ground hugging flow of either dry (Chuang et al., 2007;Sullivan et al., 2001) or wet origin (Bhardwaj et al., 2017;Ferguson & Lucchitta, 1984). ...
... Our observation that slope streaks form along fresh boulder tracks informs the debate on the origin for the slope streaks, that is, whether they form by dry (Chuang et al., 2007;Sullivan et al., 2001;Williams, 1991) or wet (Bhardwaj et al., 2019;Ferguson & Lucchitta, 1984;Ferris et al., 2002) processes. Our observations show (Figure 3 and Figures S9-S11 in Supporting Information S1) that slope streaks originating from BFE tracks are randomly distributed with no latitudinal preference, and we find no evidence that the boulder falls themselves are related to wet processes. ...
Boulder falls are an archives of recent surface activity on Mars, however, determining how recently they fell remains elusive. Our multitemporal HiRISE image analysis shows that new tracks are characterized by a herringbone‐like ejecta pattern at each boulder bounce that we call boulder fall ejecta (BFE). First systematic survey of BFE revealed ∼4,500 tracks whose total integrated track length is ∼900 km. Our BFE longevity analysis reveals that these tracks likely formed in the last few decades. From few examples we also observed slope streaks originating from BFE tracks, providing additional evidence favoring a dry origin theory. BFE fade in as little as ∼2 to 4 Mars years, whereas, others can persist >6 Mars years suggesting differential weathering. Nearly 30% of BFE are observed in the Cerberus Fossae region, which suggests it is one of the most seismically active regions. Thus, BFE can be used to recognize very recent surface processes on planetary surfaces.
... (D-F) Light-toned materials within Gully 5, Gully 10, and Gully 1; ESP_032012_1415, ESP_048824_1420, and ESP_013067_1470. (G) Slope streak exposing dark substrate, likely from dust avalanching(Dundas, 2020;Sullivan et al., 2001); ESP_058424_2035. (H) Mars Science Laboratory (bright blue dot to the west in the image) landing site a few sols after landing. ...
... The landing process blows off dust, exposing a darker substrate around the rover near a relatively dusty area to the east; ESP_028335_1755. (I) Slope streak exposing dark substrate, likely from dust avalanching(Dundas, 2020;Sullivan et al., 2001); ESP_046740_2175. All images are HiRISE false-color (IRB) and individually contrast-stretched. ...
Midlatitude slopes on Mars are mantled by deposits proposed to contain H2O ice and dust, overlaid by a desiccated lag. However, direct evidence of their volatile content is lacking. Here we present novel evidence of light‐toned materials within midlatitude gully alcoves eroded into these mantles. The appearance and Lambert albedo of these materials suggests that they are either dust or H2O ice. We interpret them to be H2O ice because it is unlikely for a short‐term, localized dust deposit to form only within the mantle walls. The temperatures are generally too warm (>∼240 K) for the ice to be a frost in equilibrium. Therefore, this ice is likely similar to the dusty ice documented within midlatitude scarps, but with more dust, and exposed in smaller patches by slumping. It has been proposed that CO2 frosts remove the overlying lag, causing the exposed H2O ice to sublimate, liberate dust within the ice for transport, and erode gullies in the mantle. But we observe gullies eroded in wall rock that continue into the mantle, implying that the same process erodes both substrates. H2O ice melt can explain gullies eroded in the wall rock and the mantle. Numerical models show that relatively dense H2O snow on Mars melts only when it contains small amounts of dust. The observed exposure of dusty ice provides a mechanism for it to melt under some conditions and form some gullies. Access to liquid water within this ice could provide potential abodes for any extant life.
... Gullies, which are similar to small terrestrial alluvial fans found on the slopes at mid and high latitudes, are the most famous of the present Martian slope features (Malin & Edgett, 2000). At low to mid-latitudes, dark wedge-shaped features on high-albedo steep slopes are associated with downslope mass movements of the first micrometers of the surface, and are known as Slope Streaks (Sullivan et al., 2001). Dark features called Recurring Slope Linae (RSL) are also found on steep slopes that have a low albedo (McEwen et al., 2011(McEwen et al., , 2014. ...
A large number of surface phenomena (e.g., frost and ice deposits, gullies, slope streaks, recurring slope lineae) are observed on Martian slopes. Their formation is associated with specific microclimates on these slopes that have been mostly studied with one-dimensional radiative balance models to date. We demonstrate here that any Martian slope can be thermally represented by a poleward or equatorward slope, i.e., the daily average, minimum, and maximum surface temperatures depend on the North-South component of the slope. Based on this observation, we propose here a subgrid-scale parameterization to represent slope microclimates in coarse-resolution global climate models. We implement this parameterization in the Mars Planetary Climate Model and validate it through comparisons with surface temperature measurements and frost detections on sloped terrains. With this new model, we show that these slope microclimates do not have a significant impact on the seasonal CO2 and H2O cycle. Our model also simulates for the first time the heating of the atmosphere by warm plains surrounding slopes. Active gullies are mostly found where our model predicts CO frost, suggesting that the formation of gullies is mostly related to processes involving CO2 ice. However, the low thicknesses predicted there rule out mechanisms involving large amounts of ice. This model opens the way to new studies on surface-atmosphere interactions in present and past climates.
... Indeed, as shown on Figure 2 one can see 123 very clearly on the slopes of the crater many avalanches whose brightness is inversely propor-124 tional to their age. The darker they are, the more recent they are (Sullivan et al., 2001 concern that ongoing fading would significantly affect our measured rates. ...
Potential dust avalanches as aftermaths of the seismic event of S1222a detected by the SEIS/InSight seismometer are investigated. Orbital observations emphasize that the area around the estimated location shows rather flat topography with North-South ridge structures. Thermal inertia data attests that the surface is essentially composed of granular materials, including dust. Thus, only a few locations show steep slopes with fragile soil. We investigated the orbital archive and requested targeted locations to assess the avalanche rate in the area and the influence of the M 4.7, S1222a event. We find an increase in the avalanche rates when thermal inertia is low. We investigate the best location that could explain these avalanche rates from the aftermath ground deformation and discuss the implications in regards to the regional geology.
... Indeed, as shown on Figure 2 one can see 123 very clearly on the slopes of the crater many avalanches whose brightness is inversely propor-124 tional to their age. The darker they are, the more recent they are (Sullivan et al., 2001 concern that ongoing fading would significantly affect our measured rates. ...
Motivation: On May 5, 2022, the martian SEIS seismometer recorded an unprecedented M Ma W 4.7 Marsquake. The epicenter is located at 3.0 • S, 171.9 • E. The areas is barely flat with only a few N-S tectonic-like features. Most unfilled impact craters and ridges show dust avalanches (a.k.a. Slope streaks). We investigate the post-seismic outcomes in terms of avalanche triggering under today’s Mars conditions in the framework of the s1222a event.
... Site 2 captures the northern rim slope and floor of an ancient ~45 km diameter crater in Arabia Terra. The steeply sloping hillslopes have many slope streaks, believed to represent avalanches of dust [193,194,195]. Many new slope streaks have been observed and they have also been observed to fade [196,197]. ...
Very high spatial resolution imaging and topographic (3D) data play an important role in modern Mars science research and engineering applications. This work describes a set of image processing and machine learning methods to produce the “best possible” high-resolution and high-quality 3D and imaging products from existing Mars orbital imaging datasets. The research work is described in nine chapters of which seven are based on separate published journal papers. These include a) a hybrid photogrammetric processing chain that combines the advantages of different stereo matching algorithms to compute stereo disparity with optimal completeness, fine-scale details, and minimised matching artefacts; b) image and 3D co-registration methods that correct a target image and/or 3D data to a reference image and/or 3D data to achieve robust cross-instrument multi-resolution 3D and image co-alignment; c) a deep learning network and processing chain to estimate pixel-scale surface topography from single-view imagery that outperforms traditional photogrammetric methods in terms of product quality and processing speed; d) a deep learning-based single-image super-resolution restoration (SRR) method to enhance the quality and effective resolution of Mars orbital imagery; e) a subpixel-scale 3D processing system using a combination of photogrammetric 3D reconstruction, SRR, and photoclinometric 3D refinement; and f) an optimised subpixel-scale 3D processing system using coupled deep learning based single-view SRR and deep learning based 3D estimation to derive the best possible (in terms of visual quality, effective resolution, and accuracy) 3D products out of present epoch Mars orbital images. The resultant 3D imaging products from the above listed new developments are qualitatively and quantitatively evaluated either in comparison with products from the official NASA planetary data system (PDS) and/or ESA planetary science archive (PSA) releases, and/or in comparison with products generated with different open-source systems. Examples of the scientific application of these novel 3D imaging products are discussed.
... For example, avalanches generally occur on slopes between inclination 28 and 55 (McClung & Schaerer, 2006;Miklau & Sauermoser, 2011). Avalanches normally are not triggered on slopes outside this range because snow masses tend not to accumulate on such slopes (Sullivan et al., 2001). ...
Mean sea level (MSL) trend at the Arabian Gulf has been estimated based on hourly tide gauge (TG) data of seven stations at the west of the gulf (1979–2008) and multi-missions satellite altimetry monthly mean (1993–2018). Analysis exposes that MSL is rising due to global warming. Altimetry data reveals a global rising trend by about 2.8 ± 0.4 mm/year while for the Arabian Gulf, trend estimation shows higher rate by about 3.6 ± 0.4 mm/year. This value almost in agreement with previous trend estimations for the gulf by many researchers and trend values in adjacent seas such as the Red Sea and Gulf of Aden. Based on TG hourly values, sea level trend is also showing a rising trend at all stations with variable rates. For example, at Mina Salman the trend value is about 3.4 ± 0.98 mm/year which agrees with the above estimate from the altimetry data followed by values from Arrabiyah Island station; 2.4 ± 0.66 mm/year. However, not all stations reflect the same MSL trend rising rates; for example, Ras Tanura recorded the lowest value of trend followed by Jubail station by about 0.7 ± 0.31 mm/year and 1.6 ± 0.71 mm/year respectively.
... For example, avalanches generally occur on slopes between inclination 28 and 55 (McClung & Schaerer, 2006;Miklau & Sauermoser, 2011). Avalanches normally are not triggered on slopes outside this range because snow masses tend not to accumulate on such slopes (Sullivan et al., 2001). ...
Wildfires in Lebanon pose an increasing threat not only to the natural environment but also to urban settings and local communities near forests. In response to this increasing threat, the Government of Lebanon endorsed a National Strategy (i.e., the Strategy) for forest fire management (Decision No. 52/2009). The Strategy acknowledged that decisions about wildfires are best made within a risk management framework including five different components, known as the 5Rs, namely (R1) Research, information and analysis; (R2) Risk modification, including fire vulnerability reduction and prevention of harmful fires; (R3) Readiness; (R4) Response, including all means of intervention for fire suppression; and (R5) Recovery, including the rehabilitation and ecological restoration of healthy forest conditions. Various tools and instruments were essentially needed to support the implementation of each component of the Strategy. These included the use of Earth Observation (EO) data and the employment of different remote sensing techniques among others. More specifically, satellite remote sensing proved to be useful for fire risk management as EO offered precise and frequent data especially that Lebanon lacked reliable national data on fire risk. In this context, the aim of this work was to review how EO contributed to fire risk management in Lebanon before (i.e., R1, R2 and R3) and after fire occurrence (i.e., R5) while supporting forecast and early detection of fires (i.e., R4). This study started by presenting EO cases which served as background information on the potential use of satellite remote sensing throughout the 5 Rs of the Strategy. The second part presented a case study from Lebanon on the actual use of EO in fire risk management.
... Low DCI values align closely with regions of higher albedo, which suggests that the surface may be composed of small, fine-grained particles. Observations of slumping/avalanches (e.g., Sullivan et al., 2001) also suggests that some such surfaces are formed of sediment. However, it remains unclear whether this takes the form of mobile, loftable dust. ...
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.
... These dark and narrow geomorphological features are late-Amazonian (see Section 1.6.) to present-day deposits which formation processes are still unknown (fine-dust avalanches? briny flows?) ( Figure 17b) [Sullivan et al., 2001;Bhardwaj et al., 2019]. MGS also revealed geomorphological contexts with successive layers interpreted as sedimentary deposits ( Figure 17c) [Malin et al., 1998;Pelkey and Jakosky, 2002]. ...
Alteration minerals are key objects to understand the geological history of the planetary bodies' surfaces. In this work, I studied the near-infrared spectroscopic properties of opaline silica (e.g. opal) and kaolinite in order to constrain the surface paleoclimatic conditions at the surface of Mars during the past. A preliminary geomorphologic study of opaline silica-bearing deposits on Mars shows four types of deposits: aeolian deposits, hydrothermal deposits, alluvial fan and fan delta deposits, and bedrock. Spectroscopic criteria, distinguishing continental weathering opals and hydrothermal opals, show that aeolian deposits are relicts of hydrothermal deposits. Other deposits are of weathering origin, except hydrothermal deposits that have a spectral signature consistent with low-temperature hydrothermal activity. Near-infrared properties of kaolinite are proxies of its "crystalline degree". Poorly-ordered kaolinites are exclusively of continental weathering origin while well-ordered kaolinites can form either by hydrothermal activity or continental weathering alteration processes.
... The superposition by dark-toned sand dunes indicates that TARs are generally older than modern, darktoned sand dunes. As some of them are over-ridden by sand dunes, gully aprons deposits, and dark slope streaks Sullivan et al., 2001), TARs are usually interpreted as being indurated and inactive (Balme et al., 2008;Berman et al., 2011Berman et al., , 2018Sullivan et al., 2008;S. A. Wilson & Zimbelman, 2004;Zimbelman, 2000). ...
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.
... Even though the most widely accepted explanations for their formation involve dry mechanisms, such as dust avalanches following oversteepening of air fall deposits [Sullivan et al., 2001], wet mechanisms proposed for their formation include ground water discharge [Ferris et al., 2002] and percolation of chloride and perchlorate brine downward to depths of decimeters [Kreslavsky and Head, 2009]. The possibility of brine formation on Mars is key to the search for life. ...
Liquid water is essential for life on Earth. To search for conditions that could support life on Mars, we need to understand if liquid water can be present, even temporarily, at its surface and shallow subsurface. Brine is a highly concentrated saline solution that can exist in the liquid state at temperatures well below the freezing point of pure water, such as those on Mars. Water ice and perchlorate salts capable of melting this ice and producing liquid solutions have been discovered in the Martian regolith from polar to equatorial regions. In addition to melting of ice, perchlorate salts may also form a brine on Mars by deliquescence, absorbing water vapor when the relative humidity is above a certain threshold. Evidence for brine at the surface and in the shallow subsurface of Mars has been reported in the last few years, such as in its polar region at the Phoenix landing site and at mid- and low-latitudes at surface features called Recurring Slope Lineae and Slope Streaks. We have designed and developed the Michigan Mars Environmental Chamber to perform experiments at Martian conditions. We study brine formation and assess whether deliquescence and/or melting are consistent its formation, and to calibrate a variety of in-situ sensors at Martian conditions. Our chamber is equipped with a Raman spectrometer, which we use to provide reference spectra of various mixing states of liquid water, ice and perchlorate salt during brine formation. We show that perchlorate brines can be identified by analyzing the decomposed Raman spectra of the investigated samples. This serves as an important reference for future in-situ Raman spectrometers on Mars and can aid in the detection of brine formation. We find that when water vapor is the only source of water, bulk deliquescence of perchlorates is not rapid enough to occur during the short periods of the day when the environmental conditions are favorable. However, when the salts are in contact with water ice, liquid brine forms more quickly, indicating that aqueous solutions could form temporarily where salts and ice coexist in the Martian regolith. We further simulate full diurnal cycles of temperature and atmospheric water vapor at the Phoenix landing site of mixtures of ice and salt such as encountered at the Phoenix landing site and show that brine can form and stay liquid for most of the diurnal cycle. This is predicted to occur seasonally in areas of the polar region where the temperature exceeds the eutectic value and frost or snow is deposited on saline soils, or where water ice and salts coexist in the shallow subsurface. Finally, we show results of the recalibration of the relative humidity sensor of the Phoenix lander. We have use a spare engineering unit to recalibrate the sensor in the full range of Phoenix landing site conditions. This provides processed relative humidity data at Martian polar conditions to enhance our understanding of the hydrological cycle at the Phoenix landing site, which is important for potential brine formation. We conclude that deliquescence is unlikely to form temporarily habitable conditions on Mars. The most likely places to do so are regions where subsurface water ice and perchlorate salts coexists. This is most likely at the north and south polar region and parts of the mid- to low-latitudes bearing water ice.
... Site 2 captures the northern rim slope and floor of an ancient ~45 km diameter crater in Arabia Terra. The steeply sloping hillslopes have many slope streaks, believed to represent avalanches of dust [21][22][23]. Many new slope streaks have been observed and they have also been observed to fade [24,25]. ...
The ExoMars Trace Gas Orbiter (TGO)’s Colour and Stereo Surface Imaging System (CaSSIS) provides multi-spectral optical imagery at 4–5 m/pixel spatial resolution. Improving the spatial resolution of CaSSIS images would allow greater amounts of scientific information to be extracted. In this work, we propose a novel Multi-scale Adaptive weighted Residual Super-resolution Generative Adversarial Network (MARSGAN) for single-image super-resolution restoration of TGO CaSSIS images, and demonstrate how this provides an effective resolution enhancement factor of about 3 times. We demonstrate with qualitative and quantitative assessments of CaSSIS SRR results over the Mars2020 Perseverance rover’s landing site. We also show examples of similar SRR performance over 8 science test sites mainly selected for being covered by HiRISE at higher resolution for comparison, which include many features unique to the Martian surface. Application of MARSGAN will allow high resolution colour imagery from CaSSIS to be obtained over extensive areas of Mars beyond what has been possible to obtain to date from HiRISE.
... However, Stillman et al. (2020) concluded that their low-slope observations were consistent with statistical noise, and some of the measurement points of Tebolt et al. (2020) do not appear to correspond to RSL (Dundas, 2020). While these observations may need greater scrutiny, we note that Martian slope streaks on heavily dust-mantled slopes, believed by some workers to be dry dust avalanches (Baratoux et al., 2006;Sullivan et al., 2001), form on slopes as low as 10° (Brusnikin et al., 2016). Perhaps dust-sand flows can transition into flows that are like small dust avalanches in some cases. ...
Recurring slope lineae (RSL) are dark linear markings on Mars that regrow annually and likely originate from the flow of either liquid water or granular material. Following the great dust storm (or planet‐encircling dust event, PEDE) of Mars year (MY) 34, Mars Reconnaissance Orbiter/High Resolution Imaging Science Experiment has seen many more candidate RSL than in typical Mars years. They have been imaged at more than 285 unique locations from August 2018 (when the atmosphere was clearing as the PEDE decayed) to August 2019, about half (157) of which are locations where RSL have not been documented previously. In MY34, 150 active RSL sites were identified in the southern middle latitudes (SML, ‐60° to ‐30°), whereas an average of 36 active sites were observed in each previous year (MY28–33). Post‐PEDE RSL are also present during southern summer over a wider range of latitude, slope aspect, and Ls (areocentric longitude of the sun) than in prior years. These RSL sites usually show evidence for recent dust deposition: obscuration of relatively dark areas, an overall brighter and redder surface than in prior years, and dust devil tracks, which indicate dust lifting by several mechanisms. We speculate that dust‐lifting processes may initiate and sustain RSL activity. The RSL may form from flows of dust (perhaps clumped) and/or sand that is destabilized by dust movement or directly mobilized by dust devils. If this is the case, then the otherwise puzzling recurrence and year‐to‐year variability of RSL activity can be at least partly explained. The dust replenishment varies from year to year, which could explain interannual variations in RSL activity.
Ground motion from seismic events detected by the SEIS/InSight seismometer on Mars could potentially trigger dust avalanches. Our research strongly suggests that the seismic event S1000a may have triggered a significant number of dust avalanches. In contrast, following the seismic event S1222a, there was only a modest increase in avalanche occurrences. Orbital observations of the area surrounding the projected location of the S1222a quake reveal notable topographic features, such as North-South ridges and impact craters. We utilize orbital imagery to evaluate the rate of avalanches and explore how the S1222a event might have influenced this rate. The S1222a event appears to be a plausible factor contributing to the observed increase in avalanches. Our further analysis of the epicenter location aims to clarify how it aligns with the avalanches' spatial distribution, offering insights into the regional topography.
A large number of surface features (e.g., frost, gullies, slope streaks, recurring slope lineae) are observed on Martian slopes. Their activity is often associated with the specific microclimates on these slopes, which have been mostly studied with one‐dimensional radiative balance models to date. We develop here a parameterization to simulate these microclimates in 3D Global Climate Models. We first demonstrate that any Martian slope can be thermally represented by a poleward or equatorward slope, that is, the daily average, minimum, and maximum surface temperatures depend on the North‐South component of the slope. Based on this observation, we implement here a subgrid‐scale parameterization to represent slope microclimates (radiative fluxes, volatile condensation, ignoring slope winds for now) in the Mars Planetary Climate Model and validate it through comparisons with surface temperature measurements and frost detections on sloped terrains. With this new model, we show that slope microclimates do not have a significant impact on the seasonal CO2 and H2O cycles on a global scale. Furthermore, short‐scale slopes (i.e., less than ∼1 km in length) do not significantly impact the thermal state of the atmosphere. Ninety‐one percent of the active gullies are found where our model predicts CO2 frost, suggesting that their activity is related to processes involving CO2 ice. However, the low thicknesses (≤tens of cm) predicted at mid‐latitudes rule out mechanisms involving large amounts (∼meters) of ice. This model opens the way to new studies on surface‐atmosphere interactions in present and past climates.
During the last six decades of planetary exploration, rapid developments in technology have helped enable the exploration of Mars. To demonstrate the technical feasibility of off-Earth mining, new technologies are being developed to identify, remotely extract, and collect commodities under different environmental conditions. Impressive machines, tools, and operational procedures have been developed that allow scientists to study in detail the atmosphere, surface, and subsurface of Mars, progressing from flybys to orbiters to stationary landers to rovers. Key technologies have been developed to provide data for understanding and characterizing the geology, mineralogy, internal structure, atmospheric composition, and dynamics, as well as to identify the possibility of life on Mars. This makes Mars a major target for human colonization, exploration, and mining.
Research into the geological processes operating on Mars relies on interpretation of images and other data returned by unmanned orbiters, probes and landers. Such interpretations are based on our knowledge of processes occurring on Earth Terrestrial analog studies therefore play an important role in understanding the geological features observed on Mars. This 2007 book presents direct comparisons between locales on Earth and Mars, and contains contributions from leading planetary geologists to demonstrate the parallels and differences between these two neighboring planets. Mars is characterized by a wide range of geological phenomena that also occur on Earth, including tectonic, volcanic, impact cratering, eolian, fluvial, glacial and possibly lacustrine and marine processes. The book provides terrestrial analogs for data sets from Mars Global Surveyor, Mars Odyssey, Mars Exploration Rovers and Mars Express, and will therefore be a key reference for students and researchers of planetary science.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Our knowledge of Mars has changed dramatically in the past 40 years due to the wealth of information provided by Earth-based and orbiting telescopes, and spacecraft investigations. Recent observations suggest that water has played a major role in the climatic and geologic history of the planet. This textbook covers our understanding of the planet's formation, geology, atmosphere, interior, surface properties, and potential for life. This interdisciplinary textbook encompasses the fields of geology, chemistry, atmospheric sciences, geophysics, and astronomy. Each chapter introduces the necessary background information to help the non-specialist understand the topics explored. It includes results from missions through 2006, including the latest insights from Mars Express and the Mars Exploration Rovers. Containing the most up-to-date information on Mars, this textbook is essential reading for graduate courses, and an important reference for researchers.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Research into the geological processes operating on Mars relies on interpretation of images and other data returned by unmanned orbiters, probes and landers. Such interpretations are based on our knowledge of processes occurring on Earth Terrestrial analog studies therefore play an important role in understanding the geological features observed on Mars. This 2007 book presents direct comparisons between locales on Earth and Mars, and contains contributions from leading planetary geologists to demonstrate the parallels and differences between these two neighboring planets. Mars is characterized by a wide range of geological phenomena that also occur on Earth, including tectonic, volcanic, impact cratering, eolian, fluvial, glacial and possibly lacustrine and marine processes. The book provides terrestrial analogs for data sets from Mars Global Surveyor, Mars Odyssey, Mars Exploration Rovers and Mars Express, and will therefore be a key reference for students and researchers of planetary science.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
Phenomenal new observations from Earth-based telescopes and Mars-based orbiters, landers, and rovers have dramatically advanced our understanding of the past environments on Mars. These include the first global-scale infrared and reflectance spectroscopic maps of the surface, leading to the discovery of key minerals indicative of specific past climate conditions; the discovery of large reservoirs of subsurface water ice; and the detailed in situ roving investigations of three new landing sites. This an important, new overview of the compositional and mineralogic properties of Mars since the last major study published in 1992. An exciting resource for all researchers and students in planetary science, astronomy, space exploration, planetary geology, and planetary geochemistry where specialized terms are explained to be easily understood by all who are just entering the field.
According to records of the Disaster and Emergency Management Presidency, avalanches have killed 30 people per year in Turkey over the last 30 years. For example, an avalanche occurred in Görmeç, in the province of Siirt, on February 01, 1992, which killed 97 people. This paper provides information about avalanche fatalities and avalanche mitigation works in Turkey as well as qualitative risk assessment method for snow avalanches in a defined region. Figure of avalanche hazard situation is presented to construct a picture of the potential threats. In the continuation, a regional-scale qualitative risk assessment is applied in a data-sparse region exposed to snow avalanches in NE Turkey. Input data included information on previous avalanche events, avalanche release and run-out areas derived from desktop review and field mapping, and an inventory of elements at risk. It is shown how categorization of elements at risk may be useful to obtain reliable results using a scoring approach. The method may foster risk management strategies in remote areas of less-developed countries, may support the choice of appropriate mitigation and may also improve risk communication and awareness. The obtained map provides are reliable and easy to understand information where avalanches constitute risky situation in regional scale as well as where new avalanche paths may develop under favourable conditions in defined region.
With the advent of the space age, planetary geomorphology has become a stand-alone discipline. This contribution provides a summary of the different processes that have been identified to form landscapes and landforms on planetary bodies in our Solar System, including rocky planets, icy planets and moons, dwarf planets, comets and asteroids. I highlight the insights these landforms have provided into the workings of these bodies and how what has been learnt in space has often taught us new lessons about the Earth. Finally, I conclude that despite the limitations imposed by remote sensing, planetary geomorphology has a bright future in planning future missions to explore our Solar System as well as understanding the data that will be returned.
Morphological features on slope areas of Mars (such as gullies, slope streaks, and recurring slope lineae) are intriguing because they are the reflection of the mineralogy, climate, and atmosphere. However, the debate as to whether martian slope features represent dry and wet formation mechanisms remains ongoing. Finding more dry and wet terrestrial analogs is one of the means to increase our understanding of these features. On the slope areas in the Yingxiong Range, the western Qaidam Basin, we observed slope streaks and surrounding features, including gullies, debris flows, and white patches. These slope streaks are light-toned, ranging from tens of meters to more than one hundred meters long, located on the slopes less than 20°. The slope streaks at one study site were observed to disappear in the next year. The morphology of slope streaks and their relations with gullies and debris flows suggest that liquid flow played a role in the formation of slope streaks. According to the analyses of the mineralogical compositions and the particle size distributions of slope streaks, the light tone of the streak features was caused by the fine particle size of the materials carried by liquid flows. The disappearance of slope streaks occurred due to the covering of the coarse-particle materials brought by aeolian processes. The alternation of aqueous and aeolian processes led to the changes of slope streaks. The forming mechanism of slope streaks in the Qaidam Basin is not related to salts or brines, which is different from other terrestrial analogs of martian slope streaks (in Antarctica and Bolivia) reported so far. This new terrestrial analog suggests that both wet and dry processes get involved in the formation of slope streaks.
Zephyria Planum, a part of Elysium Platinia, the equatorial region of Mars, is rich in numerous pyramidal, cone and dome shaped hills thousands of meters high and several kilometers in diameter. Based on morphological analysis of their attributes and sizes by far surpassing similar features on the Earth (pingo and bulgunniakhs), these formations could be classified as large hydrolaccoliths (LHLs). The morphogenesis of these structures can be attributed to temperature changes and phase transition in the permafrost. The composition of LHLs is not fundamentally different from that of their terrestrial analogues. It consists of massive ice core covered with regolith. Signs of current activity can be observed on LHL slopes. It suggestes hydraulic connection of LHLs to underlying feeding reservoirs. HiRISE space images allow us to assume that hydrolaccoliths might undergo a geologically rapid degradation and complete destruction upon termination of subsurface supply. The LHLs of Zephyria Planum present scientific value as significant water reservoirs surrounded by waterless terrains, as well as perspective sites, where evidence of life could be discovered in ice substratum and underground feeding brines. Considering resource potential and high scientific values of the formations described in this paper, the equatorial areas, where the LHLs or similar features are located could be recommended as landing sites for missions to Mars and places for the first human settlements.
We provide an up-to-date review on the different landscapes and landforms that have been attributed to the action of liquid water in the Amazonian epoch on Mars and the current state of the art regarding their interpretation. This chapter accompanies the chapter by Dundas, where the counterarguments are presented. The Amazonian epoch is thought to be dominated by hyper-arid climate conditions hostile to surface liquid water, and our review reveals that this steady state is likely to be punctuated by episodic appearances of liquid water at the surface. The proposed sources of liquid water are varied: groundwater, thawing of surface-ice, deliquescence, ground-ice or glaciers, with triggers as variable as microclimates, climate-shifts, geothermal anomalies, and impact cratering.
Our review covers recently active surface processes in the form of slope streaks, dark dune flows, and recurring slope lineae, all hypothesized at one point or another to be seeps of liquid water. We then cover landscapes and landforms that are proposed to be a result freeze–thaw cycles in the recent past, including gullies, lobate forms on hillslopes, pingo-like mounds, low-centered polygons, patterned ground, and ice-loss landscapes. We present evidence that liquid water has been produced at the base of glacial landforms during the Amazonian, resulting in sinuous ridges (eskers), and enhanced crater-wall erosion. Liquid water brought up from depth is thought to have produced mud-volcanoes and other features related to sedimentary volcanism in the Amazonian and small fluvial channels among other features are thought to be related to melting induced by periodic impact events.
We end by summarizing the importance of the search evidence of liquid water on Mars and by proposing solutions to the current impasses where progress is hindered due to limitations in data or our understanding.
Martian surface conditions are cold and dry, unfavorable for liquid water, yet steep slopes display young and currently active features suggestive of wet processes. These include recurring slope lineae and slope streaks, gully landforms, and small lobate features. Wet origins for these features would imply surprising amounts of liquid water at the surface. However, detailed observations of the morphology and activity of these features have demonstrated that dry processes, some of them unique to the Martian environment, can account for all of them. This reconciles the contradiction between physics and geomorphology and provides a self-consistent model of a Martian surface that is very active today despite having negligible volumes of liquid water.
The exploration of the solar system has shown that mass movement is a common process on the surface of the terrestrial planets (Mercury, Venus, Mars) and on many moons, including our own. However, it is on Mars that mass movements represent a major geomorphologic force both in terms of frequency, volume (often greater than 10 km³, with a record volume of 10⁶ km³), and runout, normally longer than several tens of kilometers. The study of landslides and more in general of mass movements on Mars has important implications for assessing the rock and solid properties and is a tool for understanding the geologic and climatic history of the planet. In contrast to our planet, where a landslide deposit is erased or covered after few thousands of years, mass movements on Mars are still perfectly preserved after times that may be greater than 1 billion years, making of such impulsive events a key for understanding the conditions of the planetary surfaces deep in time. In particular, landslides and their associated primary and secondary deposits may shed light on the possible presence of water or ice on the planet at the instant of flow, which is of great astrobiological importance.
Firstly, we describe the different types of landslides on Mars. Many types are similar to those on Earth, albeit often at a larger scales. We document the characteristics of slumps and rock avalanches, most of which occur in Valles Marineris, a 4000 km-long system of 6–8 km deep gorges. Landslides in Valles Marineris exhibit a variety of morphologies on their surfaces, such as Toreva blocks, longitudinal grooves, pressure ridges, run-ups on pre-existing mounds indicating high speed of emplacement. Other forms of mass movements are dubious of at least not as common as they are on Earth. Rockfalls have been documented in some cases, but their smaller size can be spotted only with high-resolution cameras. The presence of slow-expanding lateral spreads may indicate deep clay layers. Some landforms may be interpreted as debris flows and may thus be related to water. Narrow and thin slope lineae may be replenished from under a rock cap, an occurrence that, if genuine, has astrobiological implications. Mixed ejecta-landslides are a peculiar class of movements unknown on Earth. Outside Valles Marineris, mass movements occur especially but not exclusively at the craters rims or inside outflows channels. The largest landslides on Mars and of the whole solar system, the aureoles, can be identified at the borders of the Olympus Mons volcano, with runouts up to 700 kilometers. The analysis of many events demonstrates that similar to Earth, the ratio between the fall height and the runout, which is a proxy for the friction coefficient, diminishes with the mass movement volume. This may be related to environmental constraints.
The martian surface preserves a record of aqueous fluids throughout the planet's history, but when, where, and even whether such fluids exist at the contemporary surface remains an area of ongoing research. Large water volumes remain on the planet today, but mostly bound in minerals or frozen in the subsurface, with limited direct evidence for aquifers. A role for water has been suggested to explain active surface processes monitored by orbital and landed spacecraft, such as gullies and slope streaks across a range of latitudes; however, dry mechanisms appear at least equally plausible for many active slopes. The low modern atmospheric density and cold surface temperatures challenge models for producing sufficient volumes of water to do the observed geomorphic work. The seeming ubiquity of salts in martian soils facilitates liquid stability but also has implications for the habitability of any such liquids. ▪ A thin modern atmosphere and low temperatures make pure liquid water unstable on the surface of modern Mars. ▪ Widespread salts could enhance liquid durability by lowering the freezing point and slowing evaporation. ▪ Dielectric measurements suggest active brines deep beneath the south pole and, in transient thin films, within shallow polar soils. ▪ Some characteristics of gullies, recurring slope lineae, and other active features challenge both current wet and dry formation models.
Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 49 is May 28, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
The behavior of aeolian dust, particles 1-2 microns (/m) in diameter, was analyzed in a simulated Martian environment. Three main areas have been investigated: (1) characterizing spectral and aeolian properties of Martian particles and natural wind- blown terrestrial dust in order to identify a suitable surrogate Martian dust, (2) emplacement of the material in the simulated Martian environment, and (3) experimental procedures and testing in the Martian Surface Wind Tunnel (MARSWIT). The first phase of the study involved choosing a terrestrial dust that closely resembled Martian dust. Data accumulated from various sources suggest that Martian dust is derived from the weathering of basaltic parent material, nontronite clay being a good candidate composition. A commercial clay, Carbondale Red Clay (CRC), was determined to be an appropriate surrogate Martian dust. Using a compressed air-dust ejection system, an air- entrained dust cloud was generated which settled to cover the test section in the MARSWIT. This method best replicated the natural aerodynamic settling process presumed to exist on Mars. Low-pressure experiments were performed in the MARSWIT facility located at the NASA Ames Research Center, Moffett Field, California. Two separate wind tunnel floors were used for these experiments; one provided an aerodynamically smooth-surface flow, and the other was an aerodynamically rough-surface flow. Initial and momentary particle movement was recorded at friction velocities as low as 2 m/s. However, the "dust" never reached fluid saltation threshold because individual particles less than 10/m typically do not saltate, but pass into suspension. An estimated 7 2 dust flux of 3.7 x 10- g/cm s was determined for a friction velocity of 2 m/s. This flux could suspend about i0,000 metric tons of dust per second over the surface of Mars. The dust behavior on the smooth surface was markedly different than on the rough surface under Martian conditions. Application of the processes described above to the Martian environment suggests that on rocky surfaces dust suspension would first occur, whereas smooth plains would require higher wind speeds for dust entrainment.
A variety of common eolian features on Mars have been identified from a survey of Mariner 9 and Viking orbiter images, and their regional and global distributions and orientations are discussed. Ten features have been mapped including: light and dark streaks, splotches, barchan and transverse dunes, crescentric and anomalous dunes, yardangs, wind grooves, and deflation pits. The north polar region shows a complex wind regime. Dunes and other ephemeral features reveal winds from the northwest and northeast. In the middle and low northern latitudes, northeasterly winds are the most effective winds. Southeast winds are the effective winds in most southern latitudes. Erosional features in bedrock indicate long-term and perhaps ancient wind trends, whereas depositional features may record relatively more recent winds. Deflation pits in the mantled terrain may contain the best record of both ancient and present-day winds.
Direct measurements of the optical depth above the two Viking landers are presented for a period covering the summer, fall, and winter seasons in the Northern Hemisphere, a time period during which two global dust storms occurred. The data are used to define the properties of suspended dust particles in the Martian atmosphere and to assess their role in a number of meteorological and geological processes. Major conclusions are that (1) both the radiative effects of dust particles and the thermodynamical effects of large-scale atmospheric motions have a significant impact on the vertical temperature structure; (2) Pertinent feedback effects play an important part in the generation of some local dust storms, in the expansion of local dust storms to global proportions, and in the subsequent decay of global dust storms; (3) An important mechanism for the removal of dust particles from the atmosphere is the CO2 condensation-sedimentation process; and (4) that the polar laminae are constructed from atmospheric dust and water ice is hypothesized.
We have reanalyzed three sets of Viking Lander 1 and 2 (VL1 and VL2) images of the Martian atmosphere to better evaluate the radiative properties of the atmospheric dust particles. The properties of interest are the first two moments of the size distribution, the single-scattering albedo, the dust single-scattering phase function, and the imaginary index of refraction. These properties provide a good definition of the influence that the atmospheric dust has on heating of the atmosphere. Our analysis represents a significant improvement over past analyses (Pollack et al. 1977,1979) by deriving more accurate brightnesses closer to the sun, by carrying out more precise analyses of the data to acquire the quantities of interest, and by using a better representation of scattering by nonspherical particles. The improvements allow us to better define the diffraction peak and hence the size distribution of the particles. For a lognormal particle size distribution, the first two moments of the size distribution, weighted by the geometric cross section, are found. The geometric cross-section weighted mean radius (r(sub eff)) is found to be 1.85 +/- 0.3 microns at VL2 during northern summer when dust loading was low and 1.52 +/- 0.3 microns at VL1 during the first dust storm. In both cases the best cross-section weighted mean variance (nu(eff)) of the size distribution is equal to 0.5 +/- 0.2 microns. The changes in size distribution, and thus radiative properties, do not represent a substantial change in solar energy deposition in the atmosphere over the Pollack et al. (1977,1979) estimates.
The behavior of Mars as observed by the Viking infrared thermal mapper (IRTM) is considered. The IRTM is a 28-channel, 4-telescope radiometer that operated in six spectral bands. The studies considered include observations from the interplanetary phase through data collection on November 7, 1976. During this interval, thermal mapping of the whole Martian surface has been possible. Attention is given to polar temperatures, global albedos, predawn temperatures, a thermal inertia contour map, geometry considerations, clouds, aspects of predawn warming, and observations of earth.
The Mars Pathfinder atmospheric structure investigation/meteorology (ASI/MET) experiment measured the vertical density, pressure, and temperature structure of the martian atmosphere from the surface to 160 km, and monitored surface meteorology and climate for 83 sols (1 sol = 1 martian day = 24.7 hours). The atmospheric structure and the weather record are similar to those observed by the Viking 1 lander (VL-1) at the same latitude, altitude, and season 21 years ago, but there are differences related to diurnal effects and the surface properties of the landing site. These include a cold nighttime upper atmosphere; atmospheric temperatures that are 10 to 12 degrees kelvin warmer near the surface; light slope-controlled winds; and dust devils, identified by their pressure, wind, and temperature signatures. The results are consistent with the warm, moderately dusty atmosphere seen by VL-1.
Relatively young landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the martian surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed landforms or cross-cutting features, including impact craters, small polygons, and eolian dunes. The limited size and geographic distribution of the features argue for constrained source reservoirs.
Large landslides in the Martian equatorial troughs have been investigated with respect to morphology, geologic structure of the troughs, time of emplacement, similarity to terrestrial landslides, and origin and mechanism of transport. The morphologic variations of the landslides can be attributed mainly to their degree of confinement on trough floors. The huge size of many landslides is due to their occurrence on fault scarps that may have attained several kilometers in height in the absence of vigorous fluvial erosion on Mars. The mechanical efficiency of the Martian landslides is high but in accord with predictions from large landslides on earth. -from Author
A mechanical treatment of the behaviour of snow and avalanches divided as follows: mechanism of avalanche release; avalanche motion and impact. Many uncertainties remain in even the most fundamental measures of a snow avalanche.-K.Clayton
Surface color and weathering-rind thickness of boulders on four taluses, and a reconnaissance survey elsewhere in the Craigieburn Range, New Zealand, show that talus-surface age increases downslope, indicating a decrease in probability of disturbance in this direction. Most fresh material is deposited on the upper slopes of rockfall taluses. Material may be redistributed over the middle and lower slopes by dry avalanching. The observed surface-age distributions do not support talus-accumulation models that presume addition of wedges or sheets that sequentially cover all of the surface. The presence of an older basal fringe of large boulders around taluses developed by rockfall and by snow avalanching conflicts with models predicting greatest accumulation at the talus base. Age-distributions on debris-flow taluses indicate irregular episodic accumulation of lobate debris flows, with intervening smoothing by snow glide and snow avalanching.
High-resolution pictures of talus slopes on Mars show small, dark streaks that characteristically widen downward. These streaks are different from the thin and even streaks of various albedos that stream from cliffs on talus slopes, but gradations between the two streak types occur and not all streaks can be classified with confidence. In order to study the nature and origin of the small, widening, dark streaks, all Viking pictures with a resolution of less than 100 m/pixel were surveyed. To date several hundred streaks were located, but only few are of high enough resolution to be confidently identified as widening downwards. The approximate dimensions of the streaks were measured and their shapes, numbers, position, and spacing on slopes were noted. They were plotted on a topographic map, and their relation to topography, geologic units, and regions of distinct thermal inertia and albedo were studied. Also noted was the season at which images containing streaks were acquired and the direction of illumination. Albedo measurements are in progress. Several streaks can be seen stereoscopically, but none are observed on color images. The observation of small dark streaks on talus slopes on Mars is compatible with an interpretation of their origin as eruptions of small masses of wet debris in places where steep walls intersect aquifers or where seasonal equatorial warming permits the local melting of ground ice.
The so-called yellow clouds which occur in the Martian atmosphere are generally believed to consist of granular material which has been swept from the surface by atmospheric winds. Three questions relating to these clouds are considered in this paper: the surface winds required to initiate grain motion, the particle grain sizes which may be primarily responsible for the surface obscuration, and the effects such material movement may have on the surface. It is found that unless the Martian surface is extremely rough, which appears unlikely, the wind velocities necessary to initiate grain movement are considerably greater than on the earth. If the surface atmospheric pressure is 80 mb, the required velocities do not generally exceed those observed. This is not the case if the surface pressure is 25 mb. Compatibility, for 25 mb, can be achieved, however, if the required high-velocity winds are of such short duration as to have escaped detection or if they are associated with relatively small cyclonic disturbances. It is also found that the vertical wind velocities required to maintain particles aloft are less than those required in the terrestrial atmosphere over a rather large grain size range (1 to 300 μ for 80 mb; 4 to 200 μ for 25 mb) and that particles significantly larger than generally quoted in the literature could be responsible for most surface obscurations. The possible effects of yellow cloud formation on the surface are noted. In particular, the presence or absence of dune formations can be used as an indirect indication of the surface grain size.
The Materials Adherence Experiment (MAE) on Pathfinder was designed to measure the rate of dust settling from the Martian atmosphere onto the solar array of the Mars Pathfinder Sojourner Rover. The MAE measurements indicate steady dust accumulation at a rate of about 0.28% per day. This value is consistent with the performance of the lander solar arrays, which decreased in power at an estimated rate of 0.29% per day over the same period.
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.
The nature of the transition between static and flowing regimes in
granular media, provides a key to understanding their dynamics. When a
pile of sand starts flowing, avalanches occur on its inclined free
surface. Previously, studies of avalanches in granular media have
considered the time series of avalanches in rotating drums, or in piles
continuously fed with material. Here we investigate single avalanches
created by perturbing a static layer of glass beads on a rough inclined
plane. We observe two distinct types of avalanche, with evidence for
different underlying physical mechanisms. Perturbing a thin layer
results in an avalanche propagating downhill and also laterally owing to
collisions between neighbouring grains, causing triangular tracks;
perturbing a thick layer results in an avalanche front that also
propagates upwards, grains located uphill progressively tumbling down
because of loss of support. The perturbation threshold for triggering an
avalanche is found to decrease to zero at a critical slope. Our results
may improve understanding of naturally occurring avalanches on snow
slopes where triangular tracks are also observed.
Measurements of H/L (height of drop/length of
runout) vs. volume for landslides in Valles Marineris on Mars show a
trend of decreasing H/L with increasing volume.
This trend, which is linear on a log-log plot, is parallel to but lies
above the trend for terrestrial dry rock avalanches. This result and
estimates of 104 to 105 Pa yield strength suggest
that the landslides were not water saturated, as suggested by previous
workers. The offset between the H/L vs. volume
trends shows that a typical Martian avalanche must be nearly two orders
of magnitude more voluminous than a typical terrestrial avalanche in
order to achieve the same mobility. This offset might be explained by
the effects of gravity on flows with high yield strengths. These results
should prove useful to future efforts to resolve the controversy over
the mechan-ics of long-runout avalanches.
We have used Mars Global Surveyor (MGS) Thermal Emission Spectrometer thermal emission measurements to derive the thermal inertia of the Martian surface at the ~100-km spatial scale. We have validated the use of nighttime-only measurements to derive thermal inertia as well as the use of a single wavelength band versus bolometric thermal emission measurements. We have also reanalyzed the Viking Infrared Thermal Mapper data set in a similar manner in order to allow a direct comparison between the two. Within the uncertainties of the fit of the data to the model, and the uncertainties inherent in the model, the thermal inertia has not changed substantially in the 21 years between the Viking and the MGS measurements. Although some differences are seen, they are most likely due to changes in albedo during the intervening years or to residual effects of airborne dust that are not fully accounted for in the thermal models. The thermal inertia values that we derive, between about 24 and 800 Jm-2s-1/2K-1, are thought to better represent the actual thermal inertia of the Martian surface than previous estimates.
Prior to the Mars Global Surveyor (MGS) mission, a very general view had emerged in which Martian surface materials were seen as consisting of a mixture of bright dust, dark sand, and rocks. The configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on Mars for centuries. High spatial resolution images (1.4–20 m/pixel) obtained by the MGS Mars Orbiter Camera (MOC) between September 15, 1997, and July 4, 1999, provide new information about the physical nature of the windblown material on the Martian surface and show that the pre-MGS view was much too simple. In addition to bright dust and dark sand, MOC images show evidence of bright sediment that can be transported by saltation (e.g., sand) and dark material that can be transported in suspension (e.g., silt). New views of eolian wind streaks in Daedalia Planum show that part of this region, thought to be mantled by bright dust based upon Viking and Mariner observations, is instead covered by a thin veneer of bright, windblown sand. MOC images of Sinus Sabaeus and parts of Syrtis Major, two regions thought to be sandy based upon Viking era observations, exhibit thick mantles that are inferred to consist of fine-grained sediment deposited from eolian suspension. Low albedo wind streaks in western Arabia Terra are also dark mantles, and their association with eroded crater floors and megaripples/dunes on these floors suggest that these particular wind streaks are deposits of silt-sized material that was only briefly suspended before settling to the surface. MOC images also show evidence that some eolian dunes are active on Mars today (i.e., in 1998 and 1999); the evidence for activity is largely based upon wind-and avalanche-induced streaks superposed on or eroded into seasonal frost on high-latitude dune fields. MOC images show that some other dunes are inactive, but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust. Inactive dunes are best identified by superposed features such as impact craters, landslide deposits, and yardangs.
Seasonal changes observed on the surface of Mars can in part be attributed to the transport of geological materials by wind. Images obtained by orbiting spacecraft in the 1970s showed large wind-formed features such as dunes, and revealed regional time-varying albedos that could be attributed to the effects of dust erosion and deposition. But the resolution of these images was insufficient to identify different types and sources of aeolian materials, nor could they reveal aeolian deposits other than large dunes or extensive surface coverings that were redistributed by dust storms. Here we present images of Mars with up to 50 times better resolution. These images show that martian dunes include at least two distinct components, the brighter of which we interpret to be composed of relatively soft minerals, possibly sulphates. We also find large areas of the martian surface that have several metres or more of aeolian mantle lacking obvious bedforms.
High-resolution thermal inertia mapping results are presented, derived from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) observations of the surface temperature of Mars obtained during the early portion of the MGS mapping mission. Thermal inertia is the key property controlling the diurnal surface temperature variations, and is dependent on the physical character of the top few centimeters of the surface. It represents a complex combination of particle size, rock abundance, exposures of bedrock, and degree of induration. In this work we describe the derivation of thermal inertia from TES data, present global scale analysis, and place these results into context with earlier work. A global map of nighttime thermal-bolometer-based thermal inertia is presented at ° per pixel resolution, with approximately 63% coverage between 50°S and 70°N latitude. Global analysis shows a similar pattern of high and low thermal inertia as seen in previous Viking low-resolution mapping. Significantly more detail is present in the high-resolution TES thermal inertia. This detail represents horizontal small-scale variability in the nature of the surface. Correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate-to-high thermal inertia and intermediate albedo. This new unit has a modal peak thermal inertia of 180–250 J m−2 K−1 s− and a narrow range of albedo near 0.24. The unit, covering a significant fraction of the surface, typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material. Local 3-km-resolution maps are also presented as examples of eolian, fluvial, and volcanic geology. Some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain; thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size. Outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain. Generally, correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred-meter-scale morphology and the centimeter-scale surface layer.
An experimental study was undertaken to determine how the spectral and photometric properties of representative Martian areas are affected by fallout of atmospheric dust suspended during dust forms. A laboratory apparatus was used to simulate the uniform fallout and deposition of particles 1 to 5 μm in diameter. Spectral measurements from 0.4- to 1.2-μm wavelengths and photometric measurements at several wavelengths were made for a number of Mars-analog materials before and after deposition of 6 × 10−5 to 1.5 × 10−3 g/cm2 of simulated fallout. These results indicate that the spectral and photometric properties of Martian regions can be affected significantly even by minute amounts of fallout. For instance, the reflectance at 0.56 μm of an average dark area will increase by 35% after deposition of only 9 × 10−5 g/cm2, and by 70% after deposition of 1.5 × 10−4 g/cm2. Thus the fallout from even one dust storm season (∼2 × 10−3 g/cm2) is sufficient to change significantly the spectral and photometric characteristics of the substrate material, if the fallout were ubiquitous over the surface and if no competing processes of dust removal from surface grains occured.
A time-sequential set of bolometric albedo maps for Mars has been constructed from Viking Infrared Thermal Mapper data. The maps provide global coverage in longitude for latitudes -60° to +60° at 1° by 1° spatial resolution. Individual maps are constructed under strict geometric constraints for a narrow range of Ls. The set of albedo maps spans a Martian year and includes maps before, during, and after the global dust storms of 1977. Transient brightenings associated with local dust storms or condensate clouds are apparent in some of the maps. During dust-free periods, bolometric albedo maps are generally similar to classical, visual albedo map of Mars. The distribution of bolometric surface albedos is bimodal with typical, clear-sky, Lambert albedos of 0.27 and 0.16 for bright and dark areas, respectively. Atmospheric effects strongly influence apparent surface albedos, especially for dark areas. Neither bright nor dark regions show measurable, long-term variations of bolometric albedos during clear periods.
The spatial distribution of rocks exposed at the surface of Mars has been mapped using Viking Infrared Thermal Mapper (IRTM) observations. Overall, there are no regions on the surface of Mars at a scale of 1° × 1° in latitude and longitude that are rock free. The modal value of rock abundance is 6% areal coverage, with no areas having more than 30–35% rock cover. The model developed to determine rock abundance relates the thermal emission in each of the four surface-sensing IRTM bands to temperature contrasts within the field of view, non-unit thermal emissivity due to absorption bands in the surface materials, and the absorption and scattering of the outgoing energy by atmospheric dust and water ice. Each of these effects produce characteristic spectral and diurnal signatures, allowing them to be separated. The temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine-component thermal intertia. Rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface. Low-inertia (fine), bright surfaces have fewer rocks exposed than do high-inertia (coarse), dark surfaces. Rock abundance does not correlate well with the RMS slope nor reflectivity determined from delay-Doppler radar measurements. There is, however, a possible correlation between RMS slope determined from continuous-wave radar observations. Dual-polarization radar measurements, which provide the best radar measure of small-scale roughness, indicate that the Tharsis volcanic region is very rough, whereas thermal measurements indicate very few rocks and a covering of dust. Together these observations suggest an approximately 1-m-thick mantle of fines covering a very rough subsurface. This fine material may be an aeolian deposit of dust storm fallout. Valles Marineris, together with several major channels and chaotic terrains, have high rock abundances, as does the Acidalia Planitia basin. This observed distribution may reflect the initial deposition of coarse material associated with channel formation. Syrtis Major is unique in having a high inertia but a very low rock abundance, together with low radar roughness. These observations are consistent with mantling of rocks by sand. The observed distribution of rocks and fines indicates that aeolian processes, both erosional and depositional, play a dominant role in shaping the present Martian surface.
Experimental data on avalanche impact pressures and speeds from an avalanche path at Rogers Pass, B.C., are presented for both dry and wet avalanches. Data from small load cells (645 mm ² surface) at various heights through the vertical cross-section of the avalanches show that the frequency of particle impact and hence flow density increases rapidly from top to bottom of the flow.
Data from a large circular impact plate (196 000 mm ² ) just above the ground surface show that dry avalanches have relatively higher peak pressures and relatively lower average pressures than wet avalanches for a given speed. Longitudinal wave-like characteristics in the flow may be seen for both wet and dry avalanches, but they appear to be the exception rather than the rule.
Comparison of pressure results with those of other studies shows good agreement for peak pressures, but average pressures are generally less than those of previous studies. This discrepancy is attributed to the past use of cells for which loading surface size approached typical particle size. The size effect may be demonstrated by comparison of small cell data with results from the large impact plate at Rogers Pass.
Using Viking infrared thermal mapping observations, nightime temperatures have been mapped over the northern hemisphere of Mars. The latitude range from l0oS to 50oN was mapped near midnight local time in the northern spring and temperatures compared to those predicted by a uniform thermal model. As in earlier Viking thermal mapping, three large well-defined regions are significantly cooler than expected. Four less well defined warm areas occur; two extend north beyond this coverage. Although strong local correlations exist in some areas, there is no consistent regional-scale correlation with elevation, albedo, geology, or geomorphology.-from Authors
The morphology of the landslides in the Martian equatorial troughs, the geologic structure of the troughs, the time of emplacement, the similarity to terrestrial landslides, and the origin and mechanism of transport are analyzed. About 35 large landslides well-resolved on Viking images were examined, and it is found that the major landslides cover 31,000 sq km of the trough floors, and individual slides range in area from 40 to 7000 sq km. The morphologic variations of the landslides can be attributed mainly to their degree of confinement on trough floors. Many prominent landslides appear to be of similar age and were emplaced after a major faulting that dropped the trough floors. Most sliding occurred after the created scarps were dissected into spurs, gullies, and tributary canyons. Emplacement of the landslides approximately coincided with a late episode of major eruptive activity of the Tharsis volcanoes, and it is suggested that the slides may have originated as gigantic mudflows with slump blocks at their heads. The large size of many landslides is due to the fault scarps as high as 7 km on which they formed in the absence of vigorous fluvial erosion. The landslides suggest that Mars is earthlike in some respects, which may be important for further evaluations.
The large shield volcano Olympus Mons has an aureole of grooved terrain that has been the subject of much controversy since it was first seen on Mariner 9 pictures. Various origins have been proposed for the aureole of grooved terrain. Each of the proposed origins attempts to explain certain aspects of the aureole; none satisfactorily explains all of the observed relations of the deposits to one another and to Olympus Mons. In connection with the present investigation, the proposal is made that the aureole deposits were formed by a series of great pyroclastic eruptions from several vents, fissures, or cauldrons. They occurred near the site of Olympus Mons but were emplaced prior to its construction. At least six major eruptions of pyroclastic material may have occurred.
The present analysis of emission-phase function (EPF) observations from the IR thermal mapper aboard the Viking Orbiter encompasses polar latitudes, and Viking Lander sites, and spans a wide range of solar longitudes. A multiple scattering radiative transfer model which incorporates a bidirectional phase function for the surface and atmospheric scattering by dust and clouds yields surface albedos and dust and ice optical properties and optical depths for the variety of Mars conditions. It is possible to fit all analyzed EPF sequences corresponding to dust scattering with an albedo of 0.92, rather than the 0.86 given by Pollack et al. on the bases of Viking Lander observations.
Modifications to the Toon et al. (1977) model of the particle size distribution and composition of Mars atmospheric dust are proposed, based on a variety of spacecraft and wavelength observations of the dust. A much broader, smaller particle size distribution coupled with a "palagonite-like' composition is argued to fit the complete ultraviolet-to-30-μm absorption properties of the dust better than the montmorillonite-basalt, reffvariance = 0.4 μm, rmode = 0.40 dust model of Toon et al. -from Authors
This paper presents a description of the use of Viking infrared thermal mapper (IRTM), earth-based radar, and visual observations for the study of the existence of regional dust deposits. It is pointed out that these observations provide estimates of particle size, rock abundance, surface texture, thermal emissivity, and albedo. These estimates can be used to characterize surface deposits and to determine the degree of surface mantling. Attention is given to the regolith properties, atmospheric dust properties, and a model for formation of low-inertia regions. It is found that global dust storms deposit currently approximately 25 microns of material per year in the equatorial region. Over geologic time this value may vary from 0 to 250 microns due to variations in atmospheric conditions produced by orbital variations.
The considered region comprises 81% of the surface of Mars. Thermal inertia I is a composite surface property, which is equal to the square root of the product of three factors, including the thermal conductivity, the density, and the specific heat. I is the sole thermal parameter which governs the temperature variation of a periodically heated homogeneous surface, and, as such, is the prime intermediary between remote temperature observations and their geologic interpretation. The values for the thermal inertia found imply particulate surface materials. The variation in Martian surface thermal conductivity is about two orders of magnitude. Three large regions of low-inertia material are defined. Low-inertia material always possesses high albedo. There is a general tendency for higher-thermal-inertia surfaces to be darker but exceptions occur which may be related to a thin mantling of light dust or bonding of light material.
Extremely high atmospheric wind velocities are needed to erode particulate matter on Mars. Settling velocities are roughly equivalent to terrestrial settling velocities for clay to fine sand-size particles; suspension transport may be dominant for fine particles on Mars. Yellow clouds suggest that required threshold erosion velocities are reached and that a great deal of fine-grained material is carried in suspension. Yellow cloud origins are concentrated over the southern latitudes and areas of major topographic relief. The cloud distribution pattern suggests that high threshold velocities are attained by transient atmospheric disturbances such as slope winds and dust devils.-
A new wavelength-dependent model of the single-scattering properties of the Martian dust is presented. The model encompasses the solar wavelengths (0.3 to 4.3 micrometers at 0.02 micrometer resolution) and does not assume a particular mineralogical composition of the particles. We use the particle size distribution, shape, and single-scattering properties at Viking Lander wavelengths presented by Pollack et al. [1995]. We expand the wavelength range of the aerosol model by assuming that the atmospheric dust complex index of refraction is the same as that of dust particles in the bright surface geologic units. The new wavelength-dependent model is compared to observations taken by the Viking Orbiter Infrared Thermal Mapper solar channel instrument during two dust storms. The model accurately matches afternoon observations and some morning observations. Some of the early morning observations are much brighter than the model results. The increased reflectance can be ascribed to the formation of a water ice shell around the dust particles, thus creating the water ice clouds which Colburn et al. [1989], among others, have predicted.
Thermal and albedo mapping of Mars during the Viking Primary Mission Measurement of the settling rate of atmospheric dust on Mars by the MAE instrument on Mars Pathfinder
- H H Kieffer
- T Z Martin
- A R Peterfreund
- B M Jakosky
- E D Miner
- F D Palluconi Landis
- P P Jenkins
Kieffer, H. H., T. Z. Martin, A. R. Peterfreund, B. M. Jakosky, E. D. Miner, and F. D. Palluconi, Thermal and albedo mapping of Mars during the Viking Primary Mission, J. Geophys. Res., 82, 4249-4291, 1977. Landis, G. A., and P. P. Jenkins, Measurement of the settling rate of atmospheric dust on Mars by the MAE instrument on Mars Pathfinder, J. Geophys. Res., 105, 1855-1857, 2000. Lucchitta, B. K, Landslides in Vailes Marineris, Mars,.L Geoph. vs. Res., 84, 8097-8113, 1979.
Mars: Experimental study of albedo changes caused by dust fallout Aeolian behavior of dust in a simulated Martian environment
- E N Wells
- J Veverka
- P Thomas
- B R White
- B M Lacchia
- R Greeley
- R N Leach
- I E Whitehouse
- M J Mcsaveney
Wells, E. N., J. Veverka, and P. Thomas, Mars: Experimental study of albedo changes caused by dust fallout, Icarus, 58, 331-338, 1984. White, B. R., B. M. Lacchia, R. Greeley, and R. N. Leach, Aeolian behavior of dust in a simulated Martian environment, J. Geophys. Res., 102, 25,629-25,640, 1997. Whitehouse, I. E., and M. J. McSaveney, Diachronous talus surfaces in the Southern Alps, New Zealand, and their implications to talus accumulation, Arct. All). Res., 15, 53-64, 1983.
MASS MOVEMENT SLOPE STREAKS ON MARS -100 -200 -300 -400 40':' 33':' 25':' 23
- Sullivan Et Al
- Sullivan
- Al
23,626 SULLIVAN ET AL.' MASS MOVEMENT SLOPE STREAKS ON MARS -100 -200 -300 -400 40':' 33':' 25':' 23,628 SULLIVAN ET AL.' MASS MOVEMENT SLOPE STREAKS ON MARS -lOO -200
Avalanche release Time variability of Martian bolometric albedo Properties and effects of dust suspended in the Martian atmosphere
- R I Perla
- L K Pieskor
- E D Miner
- J B Pollack
- D S Colburn
- F M Flaser
- R Kahn
- C E Carlson
- D C Pidek
Perla, R. I., Avalanche release, motion, and impact, in Dynamics of Snow and Ice Massex, edited by S.C. Colbeck, pp. 397-462, Academic, San Dingo, Cahf., 1980. Pieskor, L. K., and E. D. Miner, Time variability of Martian bolometric albedo, Icarus, 45, 179-201, 1981. Pollack, J. B., D. S. Colburn, F. M. Flaser, R. Kahn, C. E. Carlson, and D. C. Pidek, Properties and effects of dust suspended in the Martian atmosphere, J. Geol)hys. Res., 84, 2929-2945, 1979. Pollack, J. B., M. E. Ockert-Bell, and M. K. Shepard, Viking Lander image analysis of Martian atmospheric dust,.1. Geophys. Res., 100, 5235-5250, 1995.
Evidence for recent groundwater seepage and surthce runoff on Mars, &'ience Characteristics of flowing snow and avalanche impact pressures
- M C Maltn
- K S Edgett
- D Mcclung
- P Schaerer
Maltn, M. C., and K. S. Edgett, Evidence for recent groundwater seepage and surthce runoff on Mars, &'ience, 288, 2330-2335, 2000. McClung, D., and P. Schaerer, Characteristics of flowing snow and avalanche impact pressures, Ann. of Glaciol., 6, 9-14, 1985. McClung, D., and P. Schaerer, Avalanche Handbook, 272 pp., Mountaineers, Seattle, Wash., 1993.
Lucchitta Dark streaks on talus slopes Mars Reports of the Planetary Geology Program
- H M B K Ferguson