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Abstract

During an eruption, time scales of topographic change are fast and involve vertical and planimetric evolution of millimeters to meters as the event progresses. Repeat production of high spatial resolution terrain models of lava flow fields over time scales of a few hours is thus a high-value capability in tracking the buildup of the deposit. Among the wide range of terrestrial and aerial methods available to collect such topographic data, the use of an unmanned aerial vehicle (UAV) as an acquisition platform, together with structure from motion (SfM) photogrammetry, has become especially useful. This approach allows high-frequency production of centimeter-scale terrain models over kilometer-scale areas, including dangerous and inaccessible zones, with low cost and minimal hazard to personnel. This study presents the application of such an integrated UAV-SfM method to generate a high spatial resolution digital terrain model and orthomosaic of Mount Etna’s January–February 1974 lava flow field. The SfM method, applied to images acquired using a UAV platform, enabled the extraction of a very high spatial resolution (20 cm) digital elevation model and the generation of a 3-cm orthomosaic covering an area of 1.35 km2. This spatial resolution enabled us to analyze the morphology of sub-meter-scale features, such as folds, blocks, and cracks, over kilometer-scale areas. The 3-cm orthomosaic allowed us to further push the analysis to centimeter-scale grain size distribution of the lava surface. Using these data, we define three types of crust structure and relate them to positions within a channel-fed ʻaʻā flow system. These crust structures are (i) flow parallel shear lines, (ii) raft zones, and (iii) folded zones. Flow parallel shear lines are found at the channel edges, and are 2-m-wide and 0.25-m-deep zones running along the levee base and in which cracking is intense. They result from intense shearing between the moving channel lava and the static levee lava. In zones where initial levees are just beginning to form, these subtle features are the only marker that delimits the moving lava from the stagnant marginal lava. Rafts generally form as the system changes from a stable to a transitional channel regime. Over this 170-m-long zone, the channel broadens from 8 to 70 m and rafts are characterized by topographically higher and poorly cracked areas, surrounded by lower, heavily cracked areas. We interpret the rafts as forming due to breakup of crust zones, previously moving in a coherent manner in the narrow proximal channel reach. Folded zones involve arcuate, cross-flow ridges with their apexes pointing down-flow, where ridges have relatively small clasts and depressions are of coarser-grained breccia. Our folds have wavelengths of 10 m and amplitudes of 1 m; are found towards the flow front, down-flow of the raft zones; and are associated with piling up of lava behind a static or slowly moving flow front. The very high spatial resolution topographic data available from UAV-SfM allow us to resolve surfaces where roughness has a vertical and horizontal scale of variation that is less than 1 m. This is the case over pāhoehoe and ʻaʻā flow surfaces, and thus allows us to explore those new structures that are only apparent in the sub-metric data. Moreover, during future eruptions, the possibility to acquire such information in near-real time will allow a prompt analysis of developing lava flow fields and structures therein, such as developing lava channel systems, so as to contribute to timely hazard assessment, modeling, and projections.

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... To overcome these limitations, the use of different sensors mounted on Unmanned Aerial Vehicles (UAVs) for the monitoring of volcanic eruptions is gaining prominence as a complement to satellite remote sensing (Andaru et al., 2021;Pering et al., 2020;Zorn et al., 2020). There are few studies that have employed UAVs in the assessment of volcanic eruptions assessment to: evaluate their geomorphological description and elaborate digital terrain models (Darmawan et al., 2018;Favalli et al., 2018;; measure the volcanic gas composition of the ash column (Kazahaya et al., 2019;Liu et al., 2019;Mori et al., 2016); analyze the lava flow characteristics and develop models that allow the prediction of their behavior (Dietterich et al., 2017;Turner et al., 2017); or sample water at crater lakes (Terada et al., 2018). ...
... The use of UAV photogrammetry in active volcanoes has already been tested previously. Favalli et al. (2018) used a hexacopter UAV equipped with a 16-megapixel optical camera to generate a 20 cm DEM for the monitoring of the entire lava flow field of Etna's 1974 eruption. Walter et al. (2020) generated a 20 cm DEM and 10 cm/pixel orthomosaics from a quadcopter UAV equipped with a 20megapixel optical camera, for the study of the Ebeko volcano (Russia) morphology and characteristics. ...
... During a volcanic eruption, traditional ground surveys are limited (and mainly restricted) due to the danger of operating in the vicinity of fissures through which magma emanates, in areas affected by the ash column or near the lava flow front (Favalli et al., 2018;Turner et al., 2017). Although surveys in the vicinity of active volcanoes are problematic, data collection is possible with efficient and robust flight planning, considering the flight restrictions established in emergency situations (Favalli et al., 2018). ...
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Article
Monitoring for assessment of natural disasters, such as volcanic eruptions, presents a methodological challenge for the scientific community. Here, we present Unmanned Aerial Vehicles (UAVs) as a feasible, precise, rapid and safe tool for real time monitoring of the impacts of a volcanic event during the Cumbre Vieja eruption on La Palma Island, Spain (2021). UAV surveys with optical RGB (Red-Green-Blue), thermal and multispectral sensors, and a water sampling device , were carried out in different areas affected by the lava flow, including the upper volcanic edifice and the lava delta formed on the coastal fringe of the island. Our results have provided useful information for the monitoring of the advance of the lava flow and its environmental consequences during the volcanic emergency. Our data shows how La Palma island's growth, with the formation of a new lava delta of 28 ha and a total volume of lava injected into the sea of 5,138,852 m 3. Moreover, our Digital Elevation Model (DEM) simulated, with a 70 % accuracy, the prob-abilistic simulation of the possible path followed by the lava flow in the vicinity of the fissure from which the magma emanates. In addition, significant changes of seawater physical-chemical parameters were registered in coastal surface waters by the in situ seawater samples collected with the automatic water sampling device of our UAV. The first meters of the water column, due to the instant evaporation of the seawater in contact with the hot lava, produce an increase of temperature and salinity of up to 4-5°C and up to 5 units, respectively.
... Over the last 120 years, this unusual behavior has occurred only in 1974 (the studied eruption) and in 2001, where the 2001 dike also fed the 2002-2003 eruption (Neri et al., 2005). Favalli et al. (2018) used visible images of the January-March 1974 lava flow field and cone system, obtained during overflights by an unmanned aerial vehicle (UAV), to show how structure from motion (SfM) photogrammetry could be used to generate high spatial resolution digital elevation models (DEM) and orthomosaics for a lava flow field. Favalli et al. (2018) used these data to demonstrate how various products could be derived and used to assess lava surface properties, comparing with parameters derived from lower spatial resolution LiDAR DEMs to show the increase in detail and precision made possible by using the SfM-driven approach. ...
... Favalli et al. (2018) used visible images of the January-March 1974 lava flow field and cone system, obtained during overflights by an unmanned aerial vehicle (UAV), to show how structure from motion (SfM) photogrammetry could be used to generate high spatial resolution digital elevation models (DEM) and orthomosaics for a lava flow field. Favalli et al. (2018) used these data to demonstrate how various products could be derived and used to assess lava surface properties, comparing with parameters derived from lower spatial resolution LiDAR DEMs to show the increase in detail and precision made possible by using the SfM-driven approach. We here use the same DEM and orthomosaics to provide detailed geological and structural maps. ...
... These maps, when coupled with chemical and textural analyses of 29 samples collected across the lava flow field, allow us to fully characterize the lava flow units associated with the January-March 1974 eruption. Our analysis thus builds on the studies of Guest et al. (1974), Corsaro et al. (2009) andFavalli et al. (2018) to define a second end-member event-type for low flank effusive eruptions, defining and describing this eruptiontype in terms of lava morphology, dimensions, texture, chemistry, rheology, flow dynamics and emplacement history. ...
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Article
Low elevation flank eruptions represent highly hazardous events due to their location near, or in, communities. Their potentially high effusion rates can feed fast moving lava flows that enter populated areas with little time for warning or evacuation, as was the case at Nyiragongo in 1977. The January-March 1974 eruption on the western flank of Mount Etna, Italy, was a low elevation effusive event, but with low effusion rates. It consisted of two eruptive phases, separated by 23 days of quiescence, and produced two lava flow fields. We describe the different properties of the two lava flow fields through structural and morphological analyses using UAV-based photogrammetry, plus textural and rheological analyses of samples. Phase I produced lower density (∼2210 kg m-3) and crystallinity (∼37 %) lavas at higher eruption temperatures (~1080 °C), forming thinner (2-3 m) flow units with less-well-developed channels than Phase II. Although Phase II involved an identical source magma, it had higher densities (∼2425 kg m-3) and crystallinities (∼40 %), and lower eruption temperatures (~1030 °C), forming thicker (5 m) flow units with well-formed channels. These contrasting properties were associated with distinct rheologies, Phase I lavas having lower viscosities (∼103 Pa s) than Phase II (∼105 Pa s). Effusion rates were higher during Phase I (≥5 m3/s), but the episodic, short-lived nature of each lava flow emplacement event meant that flows were volume-limited and short (≤1.5 km). Phase II effusion rates were lower (≤4 m3/s), but sustained effusion led to flow units that could still extend 1.3 km, although volume limits resulted from levee failure and flow avulsion to form new channels high in the lava flow system. We present a petrologically-based model whereby a similar magma fed both phases, but slower ascent during Phase II may have led to greater degrees of degassing resulting in higher cooling-induced densities and crystallinities, as well as lower temperatures. We thus define a low effusion rate end-member scenario for low elevation effusive events, revealing that such events are not necessarily of high effusion rate and velocity, as in the catastrophic event scenarios of Etna 1669 or Kilauea 2018.
... minute to hourly intervals), and of flow front advance and inflation rates, are essential components for forecasting lava runout lengths, detecting breakouts and monitoring diversions [Dietterich and Cashman 2014;Favalli et al. 2010]. Further insight into past lava eruption rates, flow rheology, cooling and stress-strain history can be gained from mapping surface roughness of existing deposits over extents of up to tens of kilometres, and scales down to centimetres [Cashman et al. 2006;Favalli et al. 2018;Gregg and Fink 1995]. For geothermal systems with surface expressions of mud volcanoes, geysers, or fumaroles, frequent changes in thermal output, degassing, and topography reflect changes in shallow hydrothermal systems. ...
... Image sizes are typically~10-20 megapixels and, when acquired from typical altitudes of~100 m or less, result in ground resolutions of order centimetres [e.g. Favalli et al. 2018]. Although camera features such as rolling shutter and in-camera image stabilisation can visually enhance video feeds, they will degrade the quality of photogrammetric results and should be avoided or disabled if imagery are being acquired for accurate 3-D topographic modelling or multispectral data analyses [e.g. ...
... When mapping emplaced lava, spatial resolution usually takes precedence over temporal considerations, and UAS data can be sufficiently high resolution to provide insight into emplacement processes [Favalli et al. 2018]. For example, a UAS-derived visual orthomosaic (3-cm resolution) and DEM (20-cm resolution) covering 1.35 km 2 of the 1974 lava from Mt. Etna enabled mapping of sub-metre features such as folds, blocks and fractures. ...
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Article
Unoccupied aircraft systems (UAS) are developing into fundamental tools for tackling the grand challenges in volcanology; here, we review the systems used and their diverse applications. UAS can typically provide image and topographic data at two orders of magnitude better spatial resolution than space-based remote sensing, and close-range observations at temporal resolutions down to those of video frame rates. Responsive deployments facilitate dense time-series measurements, unique opportunities for geophysical surveys, sample collection from hostile environments such as volcanic plumes and crater lakes, and emergency deployment of ground-based sensors (and robots) into hazardous regions. UAS have already been used to support hazard management and decision-makers during eruptive crises. As technologies advance, increasing system capabilities, autonomy and availability, supported by more diverse and lighter-weight sensors, will offer unparalleled potential for hazard monitoring. UAS will provide opportunities for pivotal advances in our understanding of complex physical and chemical volcanic processes.
... In this work, DEM to DEM coregistration was based on the minimization of the root mean square (RMS) error between one DEM to the other by iteratively varying the three angles of rotation, the translation, and the magnification or reduction factor of one DEM [39,67,68] by using a custom-made algorithm based on the MINUIT minimization library [69]. MINUIT is a tool that can be used to find the minimum value of multiparameter functions and that can be freely downloaded (http://www.cern.ch/minuit). ...
... Independent areas, not affected by natural changes and that were as close as possible to the region of interest, were used to check the residual mismatching between the two DEMs. Note that in this case, the resulting RMS displacement error was the RMS residuals (in elevation) between one DEM and another arbitrary one chosen as a reference, rather than a true absolute error [68]. The differences between two successive properly coregistered DEMs were used to detect and outline the extent of the areas that were affected by topographic changes (Figure 4) and to calculate the volume and thickness variation inside them (Table 6). ...
... Openness down is a measure of belowground openness [71][72][73]. It has high values inside valleys, gullies, and craters, effectively resulting in the detection of cracks and fractures [68]. An openness down map derived from LiDAR showed welldefined valley directed downslope (Figure 6e), while the PLÉIADES one highlighted the artefact "cobble" texture inside the SdF (Figure 6f). ...
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Article
The geomorphological evolution of the volcanic Island of Stromboli (Italy) between July 2010 and June 2019 has been reconstructed by using multi-temporal, multi-platform remote sensing data. Digital elevation models (DEMs) from PLÉIADES-1 tri-stereo images and from Light Detection and Ranging (LiDAR) acquisitions allowed for topographic changes estimation. Data were comprised of high-spatial-resolution (QUICKBIRD) and moderate spatial resolution (SENTINEL-2) satellite images that allowed for the mapping of areas that were affected by major lithological and morphological changes. PLÉIADES tri-stereo and LiDAR DEMs have been quantitatively and qualitatively compared and, although there are artefacts in the smaller structures (e.g., ridges and valleys), there is still a clear consistency between the two DEMs for the larger structures (as the main valleys and ridges). The period between July 2010 and May 2012 showed only minor changes consisting of volcanoclastic sedimentation and some overflows outside the crater. Otherwise, between May 2012 and May 2017, large topographic changes occurred that were related to the emplacement of the 2014 lava flow in the NE part of the Sciara del Fuoco and to the accumulation of a volcaniclastic wedge in the central part of the Sciara del Fuoco. Between 2017 and 2019, minor changes were again detected due to small accumulation next to the crater terrace and the erosion in lower Sciara del Fuoco.
... The folding of lava flow surfaces has been studied across a compositional range including basalt (Macdonald 1953;Fink and Fletcher 1978;Gregg et al. 1998;Iezzi and Ventura 2000;Cashman et al. 2013;Favalli et al. 2018), andesite (Gregg et al. 1998;Warner and Gregg 2003), dacite (Gregg et al. 1998;Pyle and Elliott 2006;Lescinsky et al. 2007), and rhyolite (Fink 1980;Castro and Cashman 1999;Farquharson et al. 2015;Magnall et al. 2017). Even some extra-terrestrial lava flows with similar topographic expressions (i.e., surface ridges) have been interpreted to form via surface folding (Theilig and Greeley 1986;Gregg et al. 1998;Warner and Gregg 2003). ...
... DTMs are powerful tools for studying a range of morphological parameters and are widely used in physical volcanology (Pyle and Elliott 2006;James et al. 2007;James and Varley 2012;Westoby et al. 2012;Cashman et al. 2013;Hamilton et al. 2013;Dietterich et al. 2015;Farquharson et al. 2015;Favalli et al. 2018;Kolzenburg et al. 2018). In addition to topographic analysis, six experimental flows were chosen for video analysis. ...
... Another advantage of the wavelength ratio model is that it does not rely on the typical physical parameters such as thickness, density, mean output rate, or velocity, which can be difficult or impossible to measure in ancient or distant flows. As shown in this and other studies, determining wavelength ratios requires only topographic data, which can be produced using photogrammetry, laser and radar scanning, or total station surveys (Gregg et al. 1998;Pyle and Elliott 2006;Lescinsky et al. 2007;Favalli et al. 2018). ...
Article
Viscoelastic strain in lava flows is commonly expressed as gravity-driven buckling of the lava crust. This surface folding process creates the well-known ropy pāhoehoe texture of basaltic lavas and the ogives and surface ridges of more compositionally evolved lava flows. Previous work has shown that surface fold wavelengths are proportional to the viscosity contrast between the lava crust and core, and to the thickness of the crust. Thus, fold analysis can be an important tool for understanding lava flow rheology. We analyze fold wavelength patterns of solidified natural lava flows from the Myvatn lava fields (Iceland), Piton de La Fournaise (La Réunion), and experimental lava flows from the Syracuse University Lava Project. In each case, lava flows exhibited two dominant wavelengths, consistent with multiple generations of coaxial folding. The ratio of the two dominant wavelengths for basalt (Iceland, La Réunion) is ~ 5:1 whereas the wavelength ratio for basaltic andesite (Syracuse) is ~ 3:1, suggesting a compositional control on deformation, as proposed by previous studies. Video analysis of incrementally folded Syracuse lava crusts reveals significant non-coaxial strain, which violates the assumptions of plane strain used in crustal buckling models. These results show that interpreting lava rheology from finite strain requires careful consideration of complex three-dimensional strain fields. Despite these complexities, the correlation between fold wavelength ratios and lava flow composition persists and may provide important insight into flow characterization.
... Etna, among which ground-based surveys (Calvari et al., 1994;Frazzetta and Romano, 1984;Spampinato et al., 2011), aerial and satellite images (Coltelli et al., 2007;Del Negro et al., 2016;Ganci et al., 2018), airborne and terrestrial laser scanning (Behncke et al., 2016;Favalli et al, 2009Favalli et al, , 2010James et al., 2009). Recently, the use of photogrammetric computer vision techniques has been accepted for reconstructing and mapping the topography of a volcano, starting from photographs taken using a consumer-grade camera (e.g., Anderson et al., 2019;Biass et al., 2019;De Beni et al., 2019Farquharson et al., 2015;Favalli et al., 2018;James et al., 2020;Neri et al., 2017;Wakeford et al., 2019). Moreover, one of the most relevant advantages in using new photogrammetric methods is that they can be used to extract new information and data from images acquired in the past, when these methods and algorithms did not exist. ...
... The general workflow we used to reconstruct the 3D scene geometry by the SfM method from a set of images with unknown interior and exterior orientation is described in detail in Kolzenburg et al. (2016) and Favalli et al. (2018). The final product of the SfM method was a 3D point cloud of the imaged surface with mean point density of 0.4 pt/m 2 , which was used to generate a 4-m resolution DEM and an 0.2-m resolution orthophoto of the investigated area. ...
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Article
Mapping lava flows frequently during effusive eruptions provides crucial parameters to better understand their dynamics, in turn improving our ability to model lava flow behavior. New photogrammetric methods have recently been developed, shifting the paradigm of photogrammetry from pure method to a multidisciplinary approach able to reduce the cost of volcanic monitoring and widen the potential spectrum of application. In this work, we demonstrate how multi‐view and single‐view photogrammetry methods can be used effectively to extract accurate quantitative information from photographs taken during routine surveys over an active lava flow. One intriguing advantage of these methods is that they can re‐use images acquired previously to extract new data from past eruptions. In particular, we reconstructed quantitatively the evolution of the lava flow field emplaced during 2004–2005 at Mt. Etna, subdivided in five eruptive phases from the earliest simple lava flows to the final compound lava field about 6 months later. Our results show that, in the first week of eruption, lava field formation was characterized by an increasing lava length that followed a power law growth and by a decreasing front velocity that followed a power law as well. Thereafter, the length increasing became almost constant until the developed lava tube system was able to drain the lava for long distances, with the area inundated by lava that grew linearly in the first 20 days. Finally, we demonstrate the crucial role that the syn‐eruptive DEMs acquisition could have to improve our understanding of the emplacement dynamics of complex lava fields.
... They presented several skylights in aerial and field photographs with a description of their morphologies. Favalli et al. [22] employed an unmanned aerial vehicle (UAV)-based survey to characterize the 1974 Etna lava flows at unprecedented resolutions. They reached an important conclusion that forms the basis for our study as well, i.e., the obtained high-resolution terrain data from UAVs resolves surfaces at submeter resolution, making the identification of folds and small openings possible. ...
... The study by Favalli et al. [22] has already emphasized the importance of UAV imaging and terrain data in resolving lava surfaces and enabling identification of folds and small openings. The fact that we could characterize 81 small cave openings/folds of <1.5 m 2 average area, within a small section of the lava flow, is the proof that fine resolution datasets can be extremely useful in furthering our understanding of these landforms. ...
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Article
Volcanic-aeolian interactions and processes have played a vital role in landscape evolution on Mars. Martian lava fields and associated caves have extensive geomorphological, astrobiological, and in-situ resource utilization (ISRU) implications for future Mars missions which might be focused on subsurface exploration. Although several possible cave “skylights” of tens to >100 m diameter have been spotted in lava fields of Mars, there is a possibility of prevalence of meter-scale features which are an order of magnitude smaller and difficult to identify but could have vital significance from the scientific and future exploration perspectives. The Icelandic volcanic-aeolian environment and fissure volcanoes can serve as analogs to study lava flow-related small caves such as surface tubes, inflationary caves, liftup caves, and conduits. In the present work, we have tried to explore the usability of unmanned aerial vehicle (UAV)-derived images for characterizing a solidified lava flow and designing a sequential methodology to identify small caves in the lava flow. In the mapped area of ~0.33 km2, we were able to identify 81 small cave openings, five lava flow morphologies, and five small cave types using 2 cm/pixel high-resolution images. The results display the usefulness of UAV imaging for such analogous research, and also highlight the possibility of the widespread presence of similar small cave openings in Martian lava fields. Such small openings can facilitate optimal air circulation within the caves while sheltering the insides from physical weathering and harmful radiations. Using the available best resolution remote sensing images, we extend the analogy through the contextual and geomorphological analysis of several possible pit craters in the Tharsis region of Mars, in a region of extremely vesicular and fragile lava crust with pahoehoe-type morphology. We report two possible pit craters in this region, with diameters as small as ~20 m. The possibility that such small cave openings can lead to vast subterranean hollow spaces on Mars cannot be ruled out considering its low gravity.
... UASs have a number of advantages compared to standard airborne photogrammetric surveys and satellite imagery, as they are low cost, allow generating very high resolution maps and are temporally flexible. Therefore, the use of UAS became a powerful tool in volcanology [23,24], as it allowed the estimation of eruption volumes [25], the detection of small topographic changes and fractures [5], sampling and gas measurements [26,27], the monitoring of deformation [28] and could even reach remote sites at distances exceeding the 100 km range [29]; moreover it could be used for many other volcanologic purposes [23][24][25]. Especially at explosive volcanoes, the use of a UAS is often the only affordable way to obtain samples and high-resolution terrain models, as vividly demonstrated for the Agung crisis [30] and steam-driven explosion structures at Merapi volcano, Indonesia [31], topographic changes at the flanks of Colima, Mexico [32] and the rapid growth and collapse at the dome of Santiaguito [28] and Fuego, Guatemala [33]. ...
... UASs have a number of advantages compared to standard airborne photogrammetric surveys and satellite imagery, as they are low cost, allow generating very high resolution maps and are temporally flexible. Therefore, the use of UAS became a powerful tool in volcanology [23,24], as it allowed the estimation of eruption volumes [25], the detection of small topographic changes and fractures [5], sampling and gas measurements [26,27], the monitoring of deformation [28] and could even reach remote sites at distances exceeding the 100 km range [29]; moreover it could be used for many other volcanologic purposes [23][24][25]. Especially at explosive volcanoes, the use of a UAS is often the only affordable way to obtain samples and high-resolution terrain models, as vividly demonstrated for the Agung crisis [30] and steam-driven explosion structures at Merapi volcano, Indonesia [31], topographic changes at the flanks of Colima, Mexico [32] and the rapid growth and collapse at the dome of Santiaguito [28] and Fuego, Guatemala [33]. ...
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Article
Vulcanian explosions are hazardous and are often spontaneous and direct observations are therefore challenging. Ebeko is an active volcano on Paramushir Island, northern Kuril Islands, showing characteristic Vulcanian-type activity. In 2019, we started a comprehensive survey using a combination of field station records and repeated unoccupied aircraft system (UAS) surveys to describe the geomorphological features of the edifice and its evolution during ongoing activity. Seismic data revealed the activity of the volcano and were complemented by monitoring cameras, showing a mean explosion interval of 34 min. Digital terrain data generated from UAS quadcopter photographs allowed for the identification of the dimensions of the craters, a structural architecture and the tephra deposition at cm-scale resolution. The UAS was equipped with a thermal camera, which in combination with the terrain data, allowed it to identify fumaroles, volcano-tectonic structures and vents and generate a catalog of 282 thermal spots. The data provide details on a nested crater complex, aligned NNE-SSW, erupting on the northern rim of the former North Crater. Our catalog of thermal spots also follows a similar alignment on the edifice-scale and is also affected by topography on a local scale. This paper provides rare observations at Ebeko volcano and shows details on its Vulcanian eruption style, highlighting the relevance of structural and morphologic control for the geometry of craters and tephra fallout as well as for structurally controlled geothermal activity.
... The author developed a strategy to obtain a DEM from images from different ground camera without placing Ground Control reference Points (GCP) directly on the field. Finally, Favalli et al. (2018) realized a high resolution DEM (20 cm/px) of the Mt. Etna 1974 lava flow field with the aim to perform a morphometric analysis of lava surface. ...
... Etna eruption, the usage of UAVs was tested and successfully integrated in volcanological monitoring activity. Favalli et al. (2018) presented one of the first applications of UAV-SfM for the 3D reconstruction of the 1974 lava flow of Etna. The authors published an interesting and detailed study with very good results, carrying out the survey in optimal conditions. ...
Article
Mt. Etna (Italy) with 55 effusive events in the last six years is one of the most active volcanoes in the world, with a million people living on its flank and thousands of tourists who visit it every summer. For this reason, the lava flow monitoring for risk mitigation and Civil Protection purposes is one of the fundamental tasks of the Cartographic Laboratory of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo. This activity was traditionally performed using data collected from the field (with terrestrial GPS surveys) and from helicopter taking visible and thermal images. During the 27 February–02 March 2017 eruption the FlyEye Team, applied Unmanned Aerial Vehicles to monitor the active lava flow. Two high-resolution UAV surveys were performed on the lava flow field on the south flank of Mt. Etna, between 3050 and 2600 m a.s.l., obtaining almost 1170 images. Structure-from-Motion techniques were applied to create orthophotos and Digital Elevation Models (DEM) of the lava flow field and surroundings. The obtained DEM has a resolution of 14.2, and 20.7 cm/px for the main lava flow and the west branch, respectively. On the wall, the 96% of the lava flow field was mapped using aerial images by UAV covering an area of 0.3 × 10⁶ m². Lava flow volume was calculated with the topographic approach: difference between post- and pre-eruption surface, DEM 2017 and DEM 2014, respectively. The impossibility of spreading the GCPs homogenously distorted the resulting DEM; for this reason, it was necessary to align the lava flow point clouds, obtained from the photogrammetry software, to the basal 2014 DEM. Subtracting the two DEMs a lava flow thickness grid resulted leading to a total volume of 1.4 × 10⁶ m³ and an error estimation of about 20%. Finally, dividing the total volume for the effusion duration (63 h) a mean output rate of 6.2 m³/s resulted. The calculated volcanological parameters have the same order of magnitude of the previous activity of Mt. Etna, between 2011 and 2016. This research demonstrates that UAV photogrammetry was successfully exploited during an eruptive crisis, allowing a first fast processing, to obtain an orthophoto of the lava flow field, useful for “decision makers” and a further slower processing for the realization of a high-resolution DEM. The latter makes it possible to update the topography, another important argument for Civil Protection purpose. This paper describes a methodology that could be applied during other natural events in extreme environmental conditions.
... For each flow, the master channel was followed and the depth and width of the channel was measured with tape measure and compass-clinometer, as were the height and width of the levées. The depth of undrained lava in the channel was obtained by subtracting levée inner and outer height (see, for example, Fig. 11 of Favalli et al. (2018) for definition of the measured and derived channel/levée geometries). Where braided, the dimensions of each channel making up the total width of the channel system were measured, and the morphology of the channel lava and levée type (initial, nested, accretionary, or overflow) were noted. ...
... The variation of rheological parameters, in particular the onset and development of yield strength associated with flow crystallization, also contributes to the morphological transition incurred by lava flows (Peterson and Tilling 1989;Sehlke et al. 2014). These factors all contribute to controlling flow regime and morphology (e.g., Harris and Rowland 2001;Soule et al. 2004;Favalli et al. 2018). Glaze et al. (2014) noted that slope breaks in the terrain underlying lava flows can create eddies that disrupt the flow surface, enhancing radiative heat loss and thus reducing the distance the flow can travel. ...
Article
In this study, we examine the channel-fed ‘a‘ā lava flow system that was emplaced during a very short (less than 15 h long) eruption at Piton de la Fournaise (La Réunion) in December 2010. The system had four branches, the longest of which was 1100 m long. Three branches were emplaced over a smooth-surfaced pāhoehoe flow field with a vertical relief of 1–2 m and did not undergo burial by subsequent events. The fourth branch erupted from the same vent as the 1957 eruption and re-used the pre-existing channels of that eruption. In the proximal–medial sections of the three systems that were unconfined, we identified channelized flow sections that were characterized by the presence of either a single channel or multiple braided channels. These fed short (30–260 m long) zones of dispersed flow in the distal sections. We subsequently investigated the role of lava rheology (as controlled by downflow variations in crystal and bubble content) and pre-existing topography in triggering the transitions between single-channel and braided channel flow sections. Crystal content was 10 to 70 vol% and vesicle content was 18 to 55 vol%; cooling rates over distance (derived from glass chemistry) were 11 °C/km to 27 °C/km. However, downflow textural and thermal evolution appeared to neither affect, nor be affected by, whether the channel was single or braided. Instead, the channel network architecture could be related to even modest underlying slope variations. Here, a slope increase resulted in channel confluence, and a slope decrease resulted in channel bifurcation. This process was reversible, in that downflow slope variation could drive the channel network architecture to switch back and forth between a single channel and multiple braided channels several times along its length. Dispersed flow is always present immediately behind the flow front, irrespective of underlying topography. Three previous studies of basaltic lava flows found that steeper slopes favored braided channels, the opposite of what was observed here. We suggest that the underlying substrate and lava type may exert a control on this behavior, but further studies remain necessary.
... These errors can be greatly reduced by accurately co-registering these DEMs to the 2012 reference DEM in the benchmark areas, i.e., areas without significant morphological changes. In this work, the co-registration was based on the minimization of the root mean square (RMS) difference between each DEM and the 2012 DEM by iteratively varying the three angles of rotation, the translation, and the magnification or reduction factor of the DEM by using a custom-made algorithm based on the MINUIT numerical minimization software library (e.g., [49]). The MINUIT co-registration procedure Table 4). ...
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Article
The Sciara del Fuoco (SdF) collapse scar at Stromboli is an active volcanic area affected by rapid morphological changes due to explosive/effusive eruptions and mass-wasting processes. The aim of this paper is to demonstrate the importance of an integrated analysis of multi-temporal remote sensing (photogrammetry, COSMO-SkyMed Synthetic Aperture Radar amplitude image) and marine geophysical data (multibeam and side scan sonar data) to characterize the main morphological, textural, and volumetric changes that occurred along the SdF slope in the 2020–2021 period. The analysis showed the marked erosive potential of the 19 May 2021 pyroclastic density current generated by a crater rim collapse, which mobilized a minimum volume of 44,000 m3 in the upper Sciara del Fuoco slope and eroded 350,000–400,000 m3 of material just considering the shallow-water setting. The analysis allowed us also to constrain the main factors controlling the emplacement of different lava flows and overflows during the monitored period. Despite the morphological continuity between the subaerial and submarine slope, textural variations in the SdF primarily depend on different processes and characteristics of the subaerial slope, the coastal area, the nearshore, and “deeper” marine areas.
... As a result, it has proven to be an effective and flexible tool for topographic surveying and monitoring of landslides [4][5][6][7], rapidly documenting the damage resulting from earthquakes [8][9][10][11], or evaluating volcanic activity and landform interpretation in active volcanoes [12][13][14][15][16][17]. Just to cite a few examples from the latter subject, Turner et al., 2017 [18] [42,43]). ...
... This allowed generation of a 6-cm spatial resolution DEM and a 3-cm orthomosaic (cf. Favalli et al., 2018;Lormand et al., 2020) for a control area in the medial section of the flow field ( Fig. 2) and the flow front. The orthomosaic for the medial area also allowed estimation of tree density beyond the flow field. ...
Article
Forest destruction by ‘a‘ā lava flow is common. However, mechanical and thermal interactions between the invading lava and the invaded forest are poorly constrained. We complete mapping, thermal image and sample analyses of a channel-fed ‘a‘ā lava flow system that invaded forest on the NE flank of Mt. Etna (Italy) in 2002. These lava flows destroyed 231,000 trees, only 2% of which are still visible as felled trunks on the levees or at the channel-levee contact. The remaining 98% were first felled by the flow front, with the trunks then buried by the flow. Rare tree molds can be found at the rubble levee base where trees were buried by avalanching hot breccia and then burnt through, with a time scale for total combustion being a few days. Protruding trunks fell away from the flow, if felled by blocks avalanching down the levee flank, or became aligned with the flow if falling onto the moving stream. Estimated cooling rates (0.1–5.5 °C km⁻¹) are normal for well-insulated ‘a‘ā flow, suggesting no thermal interaction. We find the highest phenocryst concentrations (of 50–60%, above an expected value of 30–40%) in low velocity (<0.5 m s⁻¹) locations. These low velocity zones are also characterized by high trunk concentrations. Thus, the common factor behind crystal and trunk deposition is velocity. That is, when the lava slows down, crystal settling occurs and trunks are preferentially deposited. Thus, although we find no thermal or textural effects due to the presence of the forest, we do find mechanical and environmental interactions where the trees are consumed to become part of the flow.
... The distance in turn is used, together with the position of the LiDAR, to create a 3D model of the surface. Photogrammetric paradigms are instead used for generating DEMs through the standard photogrammetric methods (e.g., Baldi et al 2005;Marsella et al., 2009), and the Structure from Motion (SfM) and Multi-View Stereo Matching (MVS) methods (De Beni et al. 2019;Favalli et al., 2018;James et al. 2020;Neri et al. 2017). The latter is, recently, also used for processing PLEIADES satellite stereo-images (e.g., Bagnardi et al., 2016;Calvari et al., 2020;Di Traglia et al., 2018b;Proietti et al., 2020). ...
Chapter
Muography represents a recent and innovative tool for investigating the interior of active volcanoes. However, when dealing with frequently erupting open‐vent volcanoes such as Stromboli, any result should take into consideration the structural and morphology changes caused by the eruptive activity. This may cause either summit collapses by magma withdrawal, or morphology growth by the accumulations of a fallout from the explosive activity, or more often a combination of both. In this chapter, we present an integration of various techniques, comprising muography and digital elevation model reconstruction, together with GBInSAR ground deformation and volcano seismicity, to reconstruct the geometry of the shallow magma supply system of the volcano and its changes in time. We show how muography can display the interior of the volcano as well as its outer growth, being sensitive to all volume changes that occurred between the framed surface and the detector. This was discovered in Stromboli by comparing digital topography in the interval between 2010 and 2012, when the rapid growth of the volcano summit by the accumulation of ballistic products in the area between the crater zone and the muon detector occurred. This deposit, together with the filling in of the graben‐like depression, formed during the 2007 eruption, by fallout during the persistent explosive activity, contributed to generating a remarkable anomaly in the summit area of the volcano visualized by muography. In addition, the shallow feeding system of the volcano was surveyed by GBInSAR and seismicity, which allowed us to reconstruct its path up to a depth of a few hundred meters.
... During the last decade, the combination of imagery obtained by drones with the Structure from Motion (SfM) algorithms has been established as a useful tool for geological [31][32][33][34] and volcanological [35][36][37] studies. Sub-decimeter resolution imagery and digital elevation models obtained with this technology have been used for the study or monitoring of lava flows [38,39], and morphological changes during eruptions [40]. Moreover, surface processes occurring at volcanoes have been studied using similar methodologies and data, such as the short-and long-term deposition/erosion processes associated with rain-triggered lahars [41][42][43]. ...
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Cotopaxi is an active volcano in Ecuador, whose eruptions are characterized by producing destructive primary lahars which represent a major risk for the country. The hazard assessment related to such lahars relies largely on the knowledge of the latest event, which occurred on 26 June 1877, for either scenario definition or simulation calibration. A detailed (1:5000 scale) cartography of the deposits belonging to that eruption has been obtained in the proximal northern drainage of Cotopaxi. The cartography was performed through a combination of geological fieldwork, as well as the analysis and interpretation of high-definition imagery obtained by drone surveys combined with the Structure from Motion technology for image processing. Such imagery included red and green visible bands, and a near-infrared band, which allowed the obtention of NDVI imagery where the primary lahar deposits were identified and cartographed with support of fieldwork data. Both data sources are mutually complementary, and the final cartography would be impossible if any of them were not available. The results obtained represent a significant advance for the level of detail with respect to previous cartographic works. Moreover, they should allow an improved calibration of the new generation of numerical models that simulate lahar flow for hazard assessment at Cotopaxi.
... In this work, PLÉIADES DEM-to-DEM co-registration was based on the minimization of the root mean square (RMS) error between one DEM and another by iteratively varying the three angles of rotation, the translation, and the magnification or reduction factor of one DEM by using a custom-made algorithm based on the MINUIT minimization library (e.g. Favalli et al., 2018). MINUIT is a tool that can be used to find the minimum value of multiparameter functions (http://www. ...
Article
This study analyses the morphological changes induced by eruptive activity at Stromboli volcano (Italy) during and after events occurring during July–August 2019. This period was characterized by intense eruptive activity (two paroxysmal explosions, a two-month-long lava emission, and more intense and frequent “ordinary” explosive activity) that produced significant changes within the region known as Sciara del Fuoco, located on the most unstable, north-western flank of the volcano. Since September 2019, the eruptive activity waned but remained intense, and erosive phenomena continued to contribute to the re-shaping of the Sciara del Fuoco. The morphological changes described here were documented by integrating topographic (PLÉIADES satellite tri-stereo Digital Elevation Models) and multibeam bathymetric data, acquired before, during, and after the paroxysmal events. This allowed the study of the cumulative effect of the different processes and the characterization of the different phases of accumulation/emplacement, erosion, remobilization and re-sedimentation of the volcaniclastic materials. Data acquired at several periods between September 2018 and April 2020, allowed a comparison of the subaerial and submarine effects of the 2019 events. We find evidence of localized, significant erosion following the two pyroclastic density currents triggered by the paroxysmal explosion of the 3 July 2019. We interpret this erosion as being caused by submarine and subaerial landslides triggered by the propagation of pyroclastic density currents down the Sciara del Fuoco slope. Immediately after the explosion, a lava field accumulated on the sub-aerial slope, produced by effusive activity which lasted about two months. Subsequently, the newly emplaced lava, and in particular its breccia, was eroded, with the transfer of material onto the submarine slope. This work demonstrates how repeated topo-bathymetric surveys allowed identification of the slope processes that were triggered in response to the rapid geomorphological variations due to the eruptive activity. The surveys also allowed distinction of whether estimated volumetric losses were the result of single mass-flows or gradual erosive processes, with implications on the related geohazard. Furthermore, this work highlights how submarine slope failures can be triggered by the entry into the water of pyroclastic density currents, even of modest size. These results are important for the development and improvement of an early warning system for tsunami-induced by mass flows, both in Stromboli and for island-based and coastal volcanoes elsewhere, where landslides and pyroclastic density currents can trigger significant, potentially destructive, tsunami waves.
... In geosciences many studies have been dedicated to morphological processes (Castillo et al., 2012;James and Robson, 2012;James and Varley, 2012;Amici et al., 2013b;Casella et al., 2014;Gomez-Gutierrez et al., 2014;James and Robson, 2014;Lucieer et al., 2014;Ryan et al., 2015;Westoby et al., 2015;Woodget et al., 2015;Eltner et al., 2015;Dietrich, 2016b;Smith et al., 2016;Javernick et al., 2016;Walter et al., 2018;Deng et al., 2019;Johnson et al., 2014). Applications include runoff laboratory trials (Morgan et al., 2017), applied geology (Niethammer et al., 2012;Russell, 2016;Saito et al., 2018), geomorphology (Bemis et al., 2014;Javernick et al., 2014;Snapir et al., 2014;Dietrich, 2014;Smith and Vericat, 2015;Bakker and Lane, 2015;Dietrich, 2016a, b;Mercer and Westbrook, 2016;Pearson et al., 2017;Prosdocimi et al., 2017;Marteau et al., 2016;Balaguer-Puig et al., 2017;Vinci et al., 2017;Heindel et al., 2018;Seitz et al., 2018), glaciology (Immerzeel et al., 2017;Piermattei et al., 2016), coastal morphology (James and Robson, 2012;Casella et al., 2016;Brunier et al., 2016), volcanology (James and Robson, 2012;Bretar et al., 2013;Müller et al., 2017;Giordan et al., 2017Giordan et al., , 2018Carr et al., 2018;Favalli et al., 2018;Witt et al., 2018;Andaru and Rau, 2019;Bonali et al., 2019;De Beni et al., 2019) and geophysics (Amici et al., 2013a; Published by Copernicus Publications on behalf of the European Geosciences Union. 2882 F. Brighenti et al.: UAV survey method to monitor and analyze geological hazards et al., 2016;Di Felice et al., 2018;Zahorec et al., 2018;Federico et al., 2019). ...
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Article
Active geological processes often generate a ground surface response such as uplift, subsidence and faulting/fracturing. Nowadays remote sensing represents a key tool for the evaluation and monitoring of natural hazards. The use of unmanned aerial vehicles (UAVs) in relation to observations of natural hazards encompasses three main stages: pre- and post-event data acquisition, monitoring, and risk assessment. The mud volcano of Santa Barbara (Municipality of Caltanissetta, Italy) represents a dangerous site because on 11 August 2008 a paroxysmal event caused serious damage to infrastructures within a range of about 2 km. The main precursors to mud volcano paroxysmal events are uplift and the development of structural features with dimensions ranging from centimeters to decimeters. Here we present a methodology for monitoring deformation processes that may be precursory to paroxysmal events at the Santa Barbara mud volcano. This methodology is based on (i) the data collection, (ii) the structure from motion (SfM) processing chain and (iii) the M3C2-PM algorithm for the comparison between point clouds and uncertainty analysis with a statistical approach. The objective of this methodology is to detect precursory activity by monitoring deformation processes with centimeter-scale precision and a temporal frequency of 1–2 months.
... The recent development of real-time kinematic (RTK) global navigation satellite system (GNSS) UAVs results in even faster in situ workflows and in the production of highly accurate models. As a result, very accurate and high quality DEMs and orthomosaics have become increasingly used in the Earth sciences, allowing for centimetric to decimetric resolutions even over large areas (Favalli et al., 2018). Several recent reviews have been produced showing the applicability of UAV-based topographical surveys in volcanological research. ...
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Article
Fogo in the Cabo Verde archipelago off western Africa is one of the most prominent and active ocean island volcanoes on Earth, posing an important hazard both to local populations and at a regional level. The last eruption took place between 23 November 2014 and 8 February 2015 in the Chã das Caldeiras area at an elevation close to 1800 ma.s.l. The eruptive episode gave origin to extensive lava flows that almost fully destroyed the settlements of Bangaeira, Portela and Ilhéu de Losna. During December 2016 a survey of the Chã das Caldeiras area was conducted using a fixed-wing unmanned aerial vehicle (UAV) and real-time kinematic (RTK) global navigation satellite system (GNSS), with the objective of improving the terrain models and visible imagery derived from satellite platforms, from metric to decimetric resolution and accuracy. The main result is a very high resolution and quality 3D point cloud with a root mean square error of 0.08 m in X, 0.11 m in Y and 0.12 m in Z, which fully covers the most recent lava flows. The survey comprises an area of 23.9 km2 and used 2909 calibrated images with an average ground sampling distance of 7.2 cm. The dense point cloud, digital surface models and orthomosaics with 25 and 10 cm resolutions, a 50 cm spaced elevation contour shapefile, and a 3D texture mesh, as well as the full aerial survey dataset are provided. The delineation of the 2014/15 lava flows covers an area of 4.53 km2, which is smaller but more accurate than the previous estimates from 4.8 to 4.97 km2. The difference in the calculated area, when compared to previously reported values, is due to a more detailed mapping of the flow geometry and to the exclusion of the areas corresponding to kīpukas (outcrops surrounded by lava flows). Our study provides a very high resolution dataset of the areas affected by Fogo's latest eruption and is a case study supporting the advantageous use of UAV aerial photography surveys in disaster-prone areas. This dataset provides accurate baseline data for future eruptions, allowing for different applications in Earth system sciences, such as hydrology, ecology and spatial modelling, as well as to planning. The dataset is available for download at https://doi.org/10.5281/zenodo.4718520 (Vieira et al., 2021).
... Within the natural hazards field, there are several studies developed to address the characteristics and dynamics of floods (Murphy et al. 2016;Serban et al. 2016;Izumida et al. 2017;Cescutti et al. 2018;Langhammer and Vackova 2018;Yalcin 2018;Leal-Alves et al. 2020), earthquakes and tsunamis (Li et al. 2011;Nedjati et al. 2016;Vollgger and Cruden 2016;Dominici et al. 2017;Valkaniotis et al. 2018;Mavroulis et al. 2019;Koukouvelas et al. 2020), fires (Merino et al. 2012), volcanic processes (Mori et al. 2016;Thiele et al. 2017;Darmawan et al. 2018;Favalli et al. 2018;De Beni et al. 2019;Kazahaya et al. 2019) and landslides, which are the object of the present study (Stumpf et al. 2013;Lucieer et al. 2014;Barlow et al. 2017;Tanteri et al. 2017;Chang et al. 2018;Comert et al. 2018). ...
Article
On a global scale, from 2005 to 2019, there were 275 high-magnitude, low-frequency disasters that involved 14,172 fatalities and four million affected people. Similar patterns have taken place during longer periods of time in recent decades. This paper aims to analyse the contribution of the international landslide research community to disaster risk reduction and disaster risk management in reference to the use of Unmanned Aerial Vehicles (UAVs) in a literature review. The first section notes the relevance of disaster risk research contributions for the implementation of initiatives and strategies concerning disaster risk management. The second section highlights background information and current applications of drones in the field of hazards and risk. The methodology, which included a systematic peer review of journals in the ISI Web of Science and SCOPUS, was presented in the third section, where the results include analyses of the considered data. This study concludes that most current scholarly efforts remain rooted in hazards and post-disaster evaluation and response. Future landslide disaster risk research should be transdisciplinary in order to strengthen participation of the various relevant stakeholders in contributing to integrated disaster risk management at local, subnational, national, regional and global levels.
... Photogrammetric techniques, too, can be successfully applied to study volcanic and geothermal hazards. The applications of these techniques range from change analyses in the morphology and structures of lava domes [17][18][19][20][21] and dykes [22] to volcanic landform monitoring [23], ancient lava flow field surveys [24], volcano-tectonic surveys [25], geothermal research [26,27], and volcanic gas and plumes [28][29][30][31]. These studies can additionally include the use of optical and thermal imaging capabilities [32] to provide frequent and detailed detection and monitoring while simultaneously permitting geoscientists to detect changes in volcanic activity without putting themselves in hazardous conditions. ...
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Article
The utility of new imaging technologies to better understand hazardous geological environments cannot be overstated. The combined use of unmanned aerial vehicles (UAV) and digital photogrammetry (DP) represents a rapidly evolving technique that permits geoscientists to obtain detailed spatial data. This can aid in rapid mapping and analyses of dynamic processes that are modifying contemporary landscapes, particularly through the creation of a time series of digital data to help monitor the geomorphological evolution of volcanic structures. Our study comprises a short-term (in geological terms) monitoring program of the dynamic and diffuse Pisciarelli degas-sing structure caused by the interplay between intensive rainfall and hydrothermal activity. This area, an unstable fumarole field located several hundred meters east of the Solfatara Crater of the Campi Flegrei caldera (southern Italy), is characterized by consistent soil degassing, fluid emission from ephemeral vents, and hot mud pools. This degassing activity is episodically accompanied by seismic swarms and macroscopic morphology changes such as the appearance of vigorously degas-sing vents, collapsing landslides, and bubbling mud. In late-2019 and 2020, we performed repeated photogrammetric UAV surveys using the Structure from Motion (SfM) technique. This approach allowed us to create dense 3D point clouds and digital orthophotos spanning one year of surveys. The results highlight the benefits of photogrammetry data using UAV for the accurate remote monitoring and mapping of active volcanoes and craters in harsh and dangerous environments.
... Software and computing power have evolved very fast in last decade and the application of 135 advanced photogrammetry algorithms involving image matching and structure from motion started to allow facilitated production of high-quality digital surface models and orthophoto maps. The collection of accurate GNSS ground control points allows to generate these products with centimetre resolution and accuracy (Favalli et al 2018). The recent development of RTK UAVs allows for even faster workflows in the terrain and to produce highly accurate models. ...
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Preprint
Fogo in the Cape Verde archipelago off Western Africa is one of the most prominent and active ocean island volcanoes on Earth, posing an important hazard to both local populations and at a regional level. The last eruption took place between 23 November 2014 and 8 February 2015 in the Chã das Caldeiras area at an elevation close to 1,800 m above sea level The eruptive episode gave origin to extensive lava flows that almost fully destroyed the settlements of Bangaeira, Portela and Ilhéu de Losna. In December 2016 a survey of the Chã das Caldeiras area was conducted using a fixed-wing unmanned aerial vehicle and RTK GNSS, with the objective of improving the mapping accuracy derived from satellite platforms. The main result is an ultra-high resolution 3D point cloud with a Root Mean Square Error of 0.08 m in X, 0.11 m in Y and 0.12 m in Z, which provides unprecedented accuracy. The survey covers an area of 23.9 km2 and used 2909 calibrated images with an average ground sampling distance of 7.2 cm. A digital surface model and an orthomosaic with 25 cm resolution are provided, together with elevation contours with an equidistance of 50 cm and a 3D texture mesh for visualization purposes. The delineation of the 2014–15 lava flows shows an area of 4.53 km2 by lava, which is smaller but more accurate than the previous estimates from 4.8 to 4.97 km2. The difference in the calculated area, when compared to previously reported values, is due to a more detailed mapping of flow geometry and the exclusion of the areas corresponding to kīpukas. Our study provides an ultra high-resolution dataset of the areas affected by Fogo's latest eruption – crucial for local planning – and provides a case study to determine the advantages of ultra high-resolution UAV surveys in disaster-prone areas. The dataset is available for download at http://doi.org/10.5281/zenodo.4035038 (Vieira et al., 2020).
... UAV surveying has greatly contributed to volcanology and Earth sciences in general, including most of the real time volcanic monitoring (Turner et al., 2017;Rüdiger et al., 2018;De Beni et al., 2019;Zorn et al., 2020), volcanic photogrametry, and volcanic landform studies (Favalli et al., 2018;Jordan, 2019). Therefore, the method has been documented as a useful and high precision source of digital information, giving new insights and perspectives of volcanic topography and related processes in land formation. ...
Article
The recent and growing development and availability of unmanned aerial vehicles/systems (UAV, UAS, or “drones”) in volcanology has promoted a significant advance in volcanic surveillance of active volcanoes and in the characterization of volcanic landforms and hazards. However, in the tropics with heavy rainfall, deep volcanic soils and high relief, UAV surveying for volcanic geomorphology and volcanic hazards seems to be a relatively unexplored technique. Our aim is to present and promote innovative low-cost (<$3000) UAV applications in volcanology to reduce costs and improve high-resolution quality (up to 8 cm/pixel) data acquisition in highly dynamic landscapes. Our results contribute to the state of the art of UAV applications in volcanic landforms in tropical developing countries where nearly half of the globally active volcanoes are located. Our findings prove that UAV's are a low-cost technique that can map large extensions of geomorphological features with accessibility limitations due to geological hazards and/or private property restrictions in short time. We surveyed four active volcanic sites in Costa Rica, Central America to illustrate potential applications of UAV mapping and geomorphological analysis of lava flows, debris avalanches, lahar deposits (debris flows) and biogeomorphic landscape changes due to forest succession. Analysis derived from the digital imagery captured by the UAV allowed to determine accurate volume calculations, surface roughness characteristics, morphometric quantifications, supervised surface classifications, and in combination with hydraulic modelling to assess hazards in urban planning. We discuss the utility, limitations, and future directions of low-cost UAV surveying in the geomorphological and geological analysis of tropical volcanic landforms and processes.
... In volcanology, remote measurements using UAS now enable the collection of scientific data in previously inaccessible volcanic plumes (McGonigle et al., 2008;Shinohara, 2013;Di Stefano et al., 2018;Liu et al., 2019), or where large areal coverage is required (Darmawan et al., 2018;Favalli et al., 2018), whilst prioritizing the safety of the operator. To this end, aerial observations are now becoming integrated routinely within volcanic crisis response procedures (Turner et al., 2017;Nadeau et al., 2018;de Moor et al., 2019;Syahbana et al., 2019). ...
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Article
Long-range, high-altitude Unoccupied Aerial System (UAS) operations now enable in-situ measurements of volcanic gas chemistry at globally-significant active volcanoes. However, the extreme environments encountered within volcanic plumes present significant challenges for both air frame development and in-flight control. As part of a multidisciplinary field deployment in May 2019, we flew fixed wing UAS Beyond Visual Line of Sight (BVLOS) over Manam volcano, Papua New Guinea, to measure real-time gas concentrations within the volcanic plume. By integrating aerial gas measurements with ground-and satellite-based sensors, our aim was to collect data that would constrain the emission rate of environmentally-important volcanic gases, such as carbon dioxide, whilst providing critical insight into the state of the subsurface volcanic system. Here, we present a detailed analysis of three BVLOS flights into the plume of Manam volcano and discuss the challenges involved in operating in highly turbulent volcanic plumes. Specifically, we report a detailed description of the system, including ground and air components, and flight plans. We present logged flight data for two successful flights to evaluate the aircraft performance under the atmospheric conditions experienced during plume traverses. Further, by reconstructing the sequence of events that led to the failure of the third flight, we identify a number of lessons learned and propose appropriate recommendations to reduce risk in future flight operations.
... Some of the most striking examples of application are presented in the following sections.5.3.1 Imaging volcano-tectonic structures and their temporal evolutionDeformations linked to volcanic activity are commonly due to magma transfers, precursors of eruptions, and require almost real-time monitoring to better follow and prevent eruptions. UAV photogrammetry has great potential in monitoring such dynamic processes (lava flows monitoring)(Favalli et al. 2018; De Beni et al. 2019). Right now, most of the drones are equipped with high-resolution cameras. ...
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Article
This article presents a review of the use of Unmanned Aerial Vehicles (UAVs) in the context of geohazards. The pluri-disciplinary role of drones is outlined in numerous studies associated with mass movements, volcanology, flooding events and earthquakes. Scientific advances and innovations of several research teams around the world are presented from pre-events investigations to crisis management. More particularly, we emphasize the actual status of technology, methodologies and different applications that have emerged with the use of UAVs for each domain. It is shown that the deployment of drones in geohazards context has experienced a tremendous increase during the last 10 years, with the development of more and more miniaturized, flexible and reliable systems. The use of such technology (UAV platform, instrumentation, methodologies) is different for each domain, depending on the spatial extension and the time scale of the observed phenomenon, but also on the practical constraints associated to the civil aviation agencies regulations (outside or within urban areas, before or during a crisis…). This paper also highlights the use of recent methodologies associated with semi-automatic/automatic segmentation or deep learning for the processing of important amounts of data provided by UAVs. Finally, although still sparse, the joint use of UAVs and satellite data is progressing and remains a challenge for future studies in the context of geohazards.
... It is flexible and low-cost, and drone platforms can be equipped with high-resolution remote sensing systems [15]. Drone, or unmanned aerial vehicle (UAV), images have been widely applied to overcome problems in forestry and agriculture [15][16][17], urban vegetation [18], and even disasters such as earthquakes [19,20], landslides [21][22][23], and volcanic eruptions [24,25]. In the case of the early detection of PWD, pine trees with leaves that turn brown before autumn are categorized as PWD-indicated trees. ...
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Article
Pine wilt disease (PWD) has recently caused substantial pine tree losses in Republic of Korea. PWD is considered a severe problem due to the importance of pine trees to Korean people, so this problem must be handled appropriately. Previously, we examined the history of PWD and found that it had already spread to some regions of Republic of Korea; these became our study area. Early detection of PWD is required. We used drone remote sensing techniques to detect trees with similar symptoms to trees infected with PWD. Drone remote sensing was employed because it yields high-quality images and can easily reach the locations of pine trees. To differentiate healthy pine trees from those with PWD, we produced a land cover (LC) map from drone images collected from the villages of Anbi and Wonchang by classifying them using two classifier methods, i.e., artificial neural network (ANNs) and support vector machine (SVMs). Furthermore, compared the accuracy of two types of global positioning system (GPS) data, collected using drone and hand-held devices, for identifying the locations of trees with PWD. We then divided the drone images into six LC classes for each study area and found that the SVM was more accurate than the ANN at classifying trees with PWD. In Anbi, the SVM had an overall accuracy of 94.13%, which is 6.7% higher than the overall accuracy of the ANN, which was 87.43%. We obtained similar results in Wonchang, for which the accuracy of the SVM and ANN was 86.59% and 79.33%, respectively. In terms of the GPS data, we used two type of hand-held GPS device. GPS device 1 is corrected by referring to the benchmarks sited on both locations, while the GPS device 2 is uncorrected device which used the default setting of the GPS only. The data collected from hand-held GPS device 1 was better than those collected using hand-held GPS device 2 in Wonchang. However, in Anbi, we obtained better results from GPS device 2 than from GPS device 1. In Anbi, the error in the data from GPS device 1 was 7.08 m, while that of the GPS device 2 data was 0.14 m. In conclusion, both classifiers can distinguish between healthy trees and those with PWD based on LC data. LC data can also be used for other types of classification. There were some differences between the hand-held and drone GPS datasets from both areas.
... Recent improvements in surface morphological change detection techniques now enable much higher-resolution topographic datasets to be collected in the field, requiring less time (Barnhart and Crosby, 2013;Piras et al., 2017;Di Traglia et al., 2018;Favalli et al., 2018;Schultz-Fellenz et al., 2018). As these field collection techniques and commercial off-the-shelf topographic model development software suites offer affordable, flexible modalities for repeat data collection and processing, four-dimensional analyses lie within reach for many applications (e.g., Tannant, 2015;Warrick et al., 2017). ...
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The understanding of subsurface events that cannot be directly observed is dependent on the ability to relate surface-based observations to subsurface processes. This is particularly important for nuclear explosion monitoring, as any future clandestine tests will likely be underground. We collected ground-based lidar and optical imagery using remote, very-low-altitude unmanned aerial system platforms, before and after several underground high explosive experiments. For the lidar collections, we used a terrestrial lidar scanner to obtain high-resolution point clouds and create digital elevation models (DEMs). For the imagery collections, we used structure-from-motion photogrammetry techniques and a dense grid of surveyed ground control points to create high-resolution DEMs. Comparisons between the pre- and post-experiment DEMs indicate changes in surface topography that vary between explosive experiments with varying yield and depth parameters. Our work shows that the relationship between explosive yield and the extent of observable surface change differs from the standard scaled-depth-of-burial model. This suggests that the surface morphological change from underground high explosive experiments can help constrain the experiments' yield and depth, and may impact how such activities are monitored and verified.
... The UAV-SfM approach has been applied to study fluvial processes and environments (Fonstad et al., 2013;Izumida et al., 2017;Cook, 2017;Nesbit et al., 2018;Langhammer and Vacková, 2018;Strick et al., 2019), mass movement (Peppa et al., 2017;Clapuyt et al., 2017;Yu et al., 2017;Valkaniotis et al., 2018;Eltner et al., 2018;Cucchiaro et al., 2019;Carey et al., 2019;Peppa et al., 2019), glacial landforms (Rossini et al., 2018;Midgley et al., 2018), coastal processes and landforms (Anzidei et al., 2017;Guisado-Pintado et al., 2019), and volcanic processes (Darmawan et al., 2018;Gomez and Kennedy, 2018;De Beni et al., 2019;Dering et al., 2019). Other applications include granite tor mapping , lava flow mapping (Favalli et al., 2018), and tectonic feature mapping (Giletycz et al., 2017;Bonali et al., 2019). ...
Article
Just as geomorphology evolved from a predominantly descriptive science to largely quantitative, a new framework for geomorphology is again required as rapidly increasing human population pushes anthropic-geomorphic processes to a dominant role in the Anthropocene. Understanding these processes requires new conceptual frameworks, interdisciplinarity, and a strong technology-assisted approach. We propose a focus on the Critical Zone as a useful conceptual framework in studies of Anthropocene geomorphology. Prior studies have assessed the Anthropocene with a focus on soils, which are generally considered the unifying thread of the Critical Zone. The Critical Zone in its entirety, however, extends from the top of the canopy to the base of the groundwater system. This concept thus permits a systems approach to geomorphology across scales, addressing the extensive role of human impact on Earth surface processes. Changing climatic conditions impact the delivery of water to the Critical Zone, causing an expansion of arid lands. Land-cover alteration is decreasing infiltration, armoring surfaces, increasing surface runoff, enhancing erosion rates, and is expected to expand in the future. Thus, the benefit of using the Critical Zone as a lens to study geomorphology will result in a broad, unified interdisciplinary study of the Anthropocene. These studies can be aided by modern technology, including drones and machine-learning applications. The trend toward technology-driven studies will continue throughout the geosciences, and geomorphology will be well-aided by its use. We present a comprehensive review of the concept of the Anthropocene and the Critical Zone making a case for the necessity of a Critical Zone-approach to anthropogeomorphology.
... Patterns of roughness across the lava flow can be tied to emplacement conditions such as rate of flow and viscosity [2,3,[10][11][12]. Roughness is typically determined from topography [2,3,13] or radar backscattering [4,14,15] (e.g., root mean square (RMS) height, correlation length, and autocorrelation function). Generally, the quantification of surface roughness is derived from analyzing height variations along profiles. ...
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Roughness can be used to characterize the morphologies of a lava flow. It can be used to identify lava flow features, provide insight into eruption conditions, and link roughness pattern across a lava flow to emplacement conditions. In this study, we use both the topographic position index (TPI) and the one-dimensional Hurst exponent (H) to derive lava flow unit roughness on the 2014–2015 lava field at Holuhraun using both airborne LiDAR and photogrammetric datasets. The roughness assessment was acquired from four lava flow features: (1) spiny lava, (2) lava pond, (3) blocky surface, and (4) inflated channel. The TPI patterns on spiny lava and inflated channels show that the intermediate TPI values correspond to a small surficial slope indicating a flat and smooth surface. Lava pond is characterized by low to high TPI values and forms a wave-like pattern. Meanwhile, irregular transitions patterns from low to high TPI values indicate a rough surface that is found in blocky surface and flow margins. The surface roughness of these lava features falls within the H range of 0.30 ± 0.05 to 0.76 ± 0.04. The roughest surface is the blocky, and inflated lava flows appear to be the smoothest surface among these four lava units. In general, the Hurst exponent values in the 2014–2015 lava field at Holuhraun has a strong tendency in 0.5, both TPI and Hurst exponent successfully derive quantitative flow roughness.
... (vi) UAVs can be equipped with several types of sensors, designed for specific purposes. Thanks to the above, UAVs have been employed, over the past decade, to enhance knowledge of different types of geohazards, ranging from seismic [67,68] to landslide [69][70][71][72][73] to volcanic [74][75][76][77] and flood hazards [78,79]. With regard to the study of active tectonics and volcano-tectonics, focused on geological objects like those documented in the present work, after the first attempts with balloons [80], UAV-captured images have become a major option in the study of active faults [81][82][83][84][85][86][87][88]. ...
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Article
Iceland is one of the most recognizable and iconic places on Earth, offering an unparalleled chance to admire the most powerful natural phenomena related to the combination of geodynamic, tectonic and magmatic forces, such as active rifting, volcanic eruptions and subvolcanic intrusions. We have identified and selected 25 geosites from the Snaefellsnes Peninsula and the Northern Volcanic Zone, areas where most of the above phenomena can be admired as they unfold before the viewers' eyes. We have qualitatively assessed the selected volcano-tectonic geosites by applying a set of criteria derived from previous studies and illustrated them through field photographs, unmanned aerial vehicle (UAV)-captured images and 3-D models. Finally, we have discussed and compared the different options and advantages provided by such visualization techniques and proposed a novel, cutting-edge approach to geoheritage promotion and popularization, based on interactive, navigable Virtual Outcrops made available online.
... (vi) UAVs can be equipped with several types of sensors, designed for specific purposes. Thanks to the above, UAVs have been employed, over the past decade, to enhance knowledge of different types of geohazards, ranging from seismic [67,68] to landslide [69][70][71][72][73] to volcanic [74][75][76][77] and flood hazards [78,79]. With regard to the study of active tectonics and volcano-tectonics, focused on geological objects like those documented in the present work, after the first attempts with balloons [80], UAV-captured images have become a major option in the study of active faults [81][82][83][84][85][86][87][88]. ...
Full-text available
Article
Iceland is one of the most recognizable and iconic places on Earth, offering an unparalleled chance to admire the most powerful natural phenomena related to the combination of geodynamic, tectonic and magmatic forces, such as active rifting, volcanic eruptions and subvolcanic intrusions. We have identified and selected 25 geosites from the Snæfellsnes Peninsula and the Northern Volcanic Zone, areas where most of the above phenomena can be admired as they unfold before the viewers’ eyes. We have qualitatively assessed the selected volcano–tectonic geosites by applying a set of criteria derived from previous studies and illustrated them through field photographs, unmanned aerial vehicle (UAV)-captured images and 3-D models. Finally, we have discussed and compared the different options and advantages provided by such visualization techniques and proposed a novel, cutting-edge approach to geoheritage promotion and popularization, based on interactive, navigable Virtual Outcrops made available online.
... Topographic monitoring of lava flow fields by means of LIDAR (Neri et al., 2008;Fornaciai et al., 2010), laser scanner (Slatcher et al., 2015), Unmanned Aerial Vehicles (Turner et al., 2017;Favalli et al., 2018) and helicopter (Neri et al., 2017), has been proven to be very effective and precise in detecting and quantifying erupted products and morphological variations (Muller et al., 2017;Darmawan et al., 2018), even if these approaches are often impractical, especially in remote volcanoes, or when a large area is affected by changes due to eruptive events. An alternative is offered by optical satellites in multi-view configuration (e.g. ...
Article
Satellite remote sensing is becoming an increasingly essential component of volcano monitoring, especially at little-known and remote volcanoes where in-situ measurements are unavailable and/or impractical. Moreover the synoptic view captured by satellite imagery over volcanoes can benefit hazard monitoring efforts. By monitoring, we mean both following the changing styles and intensities of the eruption once it has started, as well as nowcasting and eventually forecasting the areas potentially threatened by hazardous phenomena in an eruptive scenario. Here we demonstrate how the diversity of remote sensing data over volcanoes and the mutual interconnection between satellite observations and numerical simulations can improve lava flow hazard monitoring in response to effusive eruption. Time-averaged discharge rates (TADRs) obtained from low spatial/high temporal resolution satellite data (e.g. MODIS, SEVIRI) are complemented, compared and fine-tuned with detailed maps of volcanic deposits with the aim of constraining the conversion from satellite-derived radiant heat flux to TADR. Maps of volcanic deposits include the time-varying evolution of lava flow emplacement derived from multispectral satellite data (e.g. EO-ALI, Landsat, Sentinel-2, ASTER), as well as the flow thickness variations, retrieved from the topographic monitoring by using stereo or tri-stereo optical data (e.g. Pléiades, PlanetScope, ASTER). Finally, satellite-derived parameters are used as input and validation tags for the numerical modelling of lava flow scenarios. Our strategy is applied to the first historic eruption of Nabro volcano (Eritrea), occurred in June 2011. This eruptive event was characterized by the extraordinary quantity of SO2 emitted into the atmosphere and the extent of the long lava flows, which had a significant impact on the inhabitants of the Eritrea-Ethiopia border region despite the low population density. Because of its remote position, little was known about this eruption regarding the quantity of volcanic deposits and the timing and mechanisms of their emplacement. We found that the total volume of deposits, calculated from differences of digital elevation models (DEMs), is about 580 × 10⁶ m³, of which about 336 × 10⁶ m³ is the volume of the main lava flow that advanced eastward beyond the caldera. Multi-spectral satellite observations indicate that the main lava flow had reached its maximum extent (~16 km) within about 4 days of the eruption onset on midnight 12 June. Lava flow simulations driven by satellite-derived parameters allow building an understanding of the advance rate and maximum extent of the main lava flow showing that it is likely to have reached 10.5 km in one day with a maximum speed of ~0.44 km/h.
... More peculiar and still unknown processes could arise from in depth studies of other basaltic volcanoes from the Earth and other planets, increasing our ability to understand and predict their behavior. A growing attention is dedicated to the use of UAV (unmanned aerial vehicles; e.g., Neri et al., 2017;Favalli et al., 2018) Dellino et al., 2010). It is a general feeling that the innovative methods will grow even more in the future, possibly coupled with virtual reality, allowing results and simulations of volcanic processes impossible to imagine nowadays. ...
... More peculiar and still unknown processes could arise from in depth studies of other basaltic volcanoes from the Earth and other planets, increasing our ability to understand and predict their behavior. A growing attention is dedicated to the use of UAV (unmanned aerial vehicles; e.g., Neri et al., 2017;Favalli et al., 2018) Dellino et al., 2010). It is a general feeling that the innovative methods will grow even more in the future, possibly coupled with virtual reality, allowing results and simulations of volcanic processes impossible to imagine nowadays. ...
... Over the past two decades, photogrammetry has been used in conjunction with other high-resolution imaging techniques to characterize the evolution of lava flows in four dimensions. Measurement techniques include stereo-imaging (James et al., , 2010James & Robson, 2014) and structure-from-motion (SfM) photogrammetry from both manned and unmanned aerial vehicles (Farquharson et al., 2015;Favalli et al., 2018;Turner, Houghton, et al., 2017;Turner, Perroy, et al., 2017) using a range of different sensors. Optical and light detection and ranging (lidar) sensors allow construction of high-resolution surface models to analyze the evolution of morphological parameters that capture the dynamics of flow emplacement (Behncke et al., 2016;Favalli et al., 2010;James et al., 2009;Kolzenburg et al., 2016). ...
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We present the evolution over 3 months of a 2016-2017 pāhoehoe flow at Kīlauea as it changed from a narrow sheet flow into a compound lava field fed by a stable system of tubes. The portion of the flow located on Kīlauea’s coastal plain was characterized using helicopter-based visible and thermal structure-from-motion photogrammetry to construct a series of georeferenced digital surface models and thermal maps on 8 different days. Results reveal key influences on the emplacement and evolution of such long-lived pāhoehoe flows. This region of the flow grew by ~12×106 m3 with a near-constant time-average discharge rate of 1.2-2.7 m3/s. The development of two tube systems is captured and shows an initial nascent tube enhanced by a narrow topographic confinement, which later inflated and created a topographic inversion that modulated the emplacement of a second flow lobe with its own tube system. The analysis of breakouts at various stages of the field’s life suggests that the evolution of the thermal and morphological properties of the flow surface reflect its maturity. Thermal properties of breakouts were used to expand the empirical relationship of breakout cooling to longer time scales. This study contributes to the long-term development and the validation of more accurate predictive models for pāhoehoe, required during the management of long-lasting lava flow crises in Hawai’i and elsewhere.
... Regarding geological hazards, UAVs have been recently used to monitor urban areas damaged after earthquakes (Baiocchi et al., 2013), soil liquefaction (Yao et al., 2019) and landslides (Gong et al., 2010;Hu et al., 2012;Rathje and Franke, 2016), as well as to detect deformation and lava flows characteristics during, and after, volcanic eruptions (Müller et al., 2017;Darmawan et al., 2018;Favalli et al., 2018;De Beni et al., 2019). UAVs have also been crucial for studying geysers and hot springs Federico et al., 2019) and post-glacial uplift (de Quay et al., 2019). ...
... The 2012 and 2017 topographic data were here co-registered by minimizing the root mean square (RMS) error between two DEMs. The methods used iteratively vary the three angles of rotation, the translation, and the magnification or reduction factor of one DEM using a custom-made algorithm based on the MINUIT minimization library [43], as described by [44][45][46]. MINUIT is a tool to find the minimum value of multi-parameter functions and can be freely downloaded (http://www.cern.ch/minuit). The LiDAR-PLEIADES DEMs co-registration was performed by calculating the minimization parameters for the whole volcano with the exclusion of the investigated areas (i.e., the SdF). ...
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In situ and remote-sensing measurements have been used to characterize the run-up phase and the phenomena that occurred during the August-November 2014 flank eruption at Stromboli. Data comprise videos recorded by the visible and infrared camera network, ground displacement recorded by the permanent-sited Ku-band, Ground-Based Interferometric Synthetic Aperture Radar (GBInSAR) device, seismic signals (band 0.02-10 Hz), and high-resolution Digital Elevation Models (DEMs) reconstructed based on Light Detection and Ranging (LiDAR) data and tri-stereo PLEIADES-1 imagery. This work highlights the importance of considering data from in situ sensors and remote-sensing platforms in monitoring active volcanoes. Comparison of data from live-cams, tremor amplitude, localization of Very-Long-Period (VLP) source and amplitude of explosion quakes, and ground displacements recorded by GBInSAR in the crater terrace provide information about the eruptive activity, nowcasting the shift in eruptive style of explosive to effusive. At the same time, the landslide activity during the run-up and onset phases could be forecasted and tracked using the integration of data from the GBInSAR and the seismic landslide index. Finally, the use of airborne and space-borne DEMs permitted the detection of topographic changes induced by the eruptive activity, allowing for the estimation of a total volume of 3.07 ± 0.37 × 10 6 m 3 of the 2014 lava flow field emplaced on the steep Sciara del Fuoco slope.
... This way, the roughness can be readily integrated into flow advance estimates when an eruption begins and as a crisis develops. As discussed earlier, new developments in remote sensing technology, including expanded satellite imagery coverage, airborne laser altimetry, and the increasing popularity of unmanned aerial systems, now allow scientists to quickly and inexpensively collect large amounts of data over areas of interest (e.g., Patrick et al. 2017;Turner et al. 2017;Favalli et al. 2018). These datasets can be harnessed to quantify bed roughness that can be integrated into flow prediction models in preparation for eruptions or implemented during an eruption. ...
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A quantitative understanding of the factors controlling lava flow emplacement is critical for both hazard assessment and mitigation and for the interpretation of past flow emplacement conditions. The influence of topography with a vertical amplitude smaller than flow thickness (i.e., substrate roughness) is currently not accounted for in most flow emplacement models and hazard estimates. Here, we measure the effect of substrate roughness on flow emplacement through experiments using analog fluids and molten basalt, complementing recent work on the interaction of lava flows with obstacles taller than flow thickness. We present results from three sets of analog experiments, in which corn syrup, polyethylene glycol, and molten basalt were each extruded onto a sloping plane covered with a series of beds of varying grain sizes. We find that flow front advance rates are impacted by bed roughness for all materials, with decreases in average velocities by up to 50% with increases of substrate grain sizes by 5–100 times, ranges analogous with topographic variations found in nature. These decreases in flow front advance velocities are equivalent to up to an order of magnitude increase in fluid viscosity. We interpret this velocity decrease to be caused by the movement of material into void spaces between substrate grains and by enhanced cooling through heat conduction to the substrate due to increased surface contact area. The difference in advance velocity with increasing grain size diminishes with time after initial emplacement as a basal boundary layer is established. Additionally, the experimental flow geometry, measured by the complexity of the flow external perimeter, became increasingly complex with increasing substrate grain size. This effect will act to both slow the forward advance of lava flows and to create irregular emplacement paths of flows moving over rough surfaces. We propose that flow emplacement models should be modified, possibly through a calibrated “effective viscosity” term, to account for bed roughness to increase accuracy in flow prediction and hazard estimation models. © 2018, This is a U.S. Government work and not under copyright protection in the US; foreign
... During flow in a channelled regime, simple shearing is limited to the edges of the channel (Borgia et al. 1983;Dragoni et al. 1986Dragoni et al. , 1992Harris et al. 2002). As a result, curvilinear ridges connect the stalled channel margins to the mobile central flow zone, also observed in other preserved flows (Fink 1980b;Lipman and Banks 1987;Favalli et al. 2018). Large-scale structures, including folds (height and width > 2 m), ramp structures and flow channels control local deformation, with channels hosting stretching lineations and smaller scale folds. ...
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The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), and preserves evidence for a multi-stage emplacement history. Due to the viscous nature of the advancing lava (10^8 to 10^10 Pa s), indicators of complex emplacement processes are preserved in the final flow. This study focuses on structural mapping of the flow to highlight the interplay of cooling, crust formation and underlying slope in the development of rhyolitic lavas. The flow is made up of two prominent lobes, small (< 0.2 m) to large (> 0.2 m) scale folding and a channelled geometry. Foliations dip at 2–4° over the flatter topography close to the vent, and up to 30–50° over steeper mid-flow topography. Brittle faults, tension gashes and conjugate fractures are also evident across flow. Heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel.We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and refolding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
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Article
Surface roughness is a commonly used parameter for the quantitative analysis and characterization of geological terrains on Earth, as well as on other planetary bodies, particularly where detailed optical data may not be available. Here, we statistically investigate if surface roughness can be used to distinguish between different lava facies in remote sensing data by examining the entire 2014–2015 Holuhraun lava flow-field in Iceland. Root-mean-square (RMS) height deviation, Hurst exponents, and breakpoints were calculated to quantify the surface roughness characteristics of eight facies using stereo-derived topographic datasets at three different pixel scales, ranging from 0.05 to 0.5 m/pixel. We show that most of the investigated lava facies (rubbly, spiny, undifferentiated rubbly–spiny, shelly, pāhoehoe, and flat-lying–knobby) are indistinguishable by surface roughness down to the 5 cm baseline, with the exception of topography-building facies like the vent-proximal edifice and the exceptionally blocky channel interior facies. Additionally, we considered baselines corresponding to radar S-band (10 cm), L-band (20 cm), and P-band (90 cm). Our findings imply that when transitional lava types are considered in addition to traditional end-members, topographic roughness data, including RMS height deviation and Hurst exponent values alone, cannot be used to uniquely identify lava facies at these baselines.
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The 2014–2015 Holuhraun eruption extruded >1 km³ of lava in a barren region of the Icelandic highlands. Due to its large volume and the abundance of data for this eruption, Holuhraun is an ideal site to investigate fissure-fed eruption products for comparison with other large lava flows-fields on Earth and other planetary bodies. To characterize lava morphologies associated with this event, we used 0.01–0.5 m/pixel image data, acquired by aerial surveys and small Unoccupied Aircraft Systems (sUAS) to create a 1:800-scale facies map that was ground-truthed using field observations during the summers of 2015–2019. Each facies region exhibits similar attributes in the remote sensing data, including albedo, surface texture, and geomorphology. However, at our mapping scale of 1:800, the facies typically include mixtures of lava types. Results show that transitional lava types (e.g., rubbly pāhoehoe, slabby pāhoehoe, and spiny pāhoehoe) dominate the 2014–2015 Holuhraun lava flow-field (83.82 km²), rather than the traditional end-members of ʻaʻā and classical pāhoehoe. At 1:800-scale, we distinguish the following eight facies (with the percentage of total flow-field area shown in parentheses): rubbly (57.35%), spiny (25.96%), undifferentiated rubbly–spiny (9.59%), shelly (5.58%), pāhoehoe (1.24%), flat-lying–knobby (0.58%), vent-proximal edifice (0.19%), and channel interior (0.16%). Field observations show that initial coherent pāhoehoe surfaces were episodically disrupted to produce slabby and rubbly textures that resemble ʻaʻā in remote sensing data. Our observations also show that continued solidification of the lava beneath brecciated surfaces can cause the surfaces of disrupted lobes to stabilize, or restabilize and undergo inflation. These factors complicate the use of surface texture as a direct indicator of emplacement style, which can change over the course of an eruption. This complexity has important implications for reconstructing the emplacement history of flow-fields on Earth and other planetary bodies.
Thesis
Lava domes are severely hazardous, mound-shaped extrusions of highly viscous lava and commonly erupt at many active stratovolcanoes around the world. Due to gradual growth and flank oversteepening, such lava domes regularly experience partial or full collapses, resulting in destructive and far-reaching pyroclastic density currents. They are also associated with cyclic explosive activity as the complex interplay of cooling, degassing, and solidification of dome lavas regularly causes gas pressurizations on the dome or the underlying volcano conduit. Lava dome extrusions can last from days to decades, further highlighting the need for accurate and reliable monitoring data. This thesis aims to improve our understanding of lava dome processes and to contribute to the monitoring and prediction of hazards posed by these domes. The recent rise and sophistication of photogrammetric techniques allows for the extraction of observational data in unprecedented detail and creates ideal tools for accomplishing this purpose. Here, I study natural lava dome extrusions as well as laboratory-based analogue models of lava dome extrusions and employ photogrammetric monitoring by Structure-from-Motion (SfM) and Particle-Image-Velocimetry (PIV) techniques. I primarily use aerial photography data obtained by helicopter, airplanes, Unoccupied Aircraft Systems (UAS) or ground-based timelapse cameras. Firstly, by combining a long time-series of overflight data at Volcán de Colima, México, with seismic and satellite radar data, I construct a detailed timeline of lava dome and crater evolution. Using numerical model, the impact of the extrusion on dome morphology and loading stress is further evaluated and an impact on the growth direction is identified, bearing important implications for the location of collapse hazards. Secondly, sequential overflight surveys at the Santiaguito lava dome, Guatemala, reveal surface motion data in high detail. I quantify the growth of the lava dome and the movement of a lava flow, showing complex motions that occur on different timescales and I provide insight into rock properties relevant for hazard assessment inferred purely by photogrammetric processing of remote sensing data. Lastly, I recreate artificial lava dome and spine growth using analogue modelling under controlled conditions, providing new insights into lava extrusion processes and structures as well as the conditions in which they form. These findings demonstrate the capabilities of photogrammetric data analyses to successfully monitor lava dome growth and evolution while highlighting the advantages of complementary modelling methods to explain the observed phenomena. The results presented herein further bear important new insights and implications for the hazards posed by lava domes.
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Article
Imaging growing lava domes has remained a great challenge in volcanology due to their inaccessibility and the severe hazard of collapse or explosion. Changes in surface movement, temperature, or lava viscosity are considered crucial data for hazard assessments at active lava domes and thus valuable study targets. Here, we present results from a series of repeated survey flights with both optical and thermal cameras at the Caliente lava dome, part of the Santiaguito complex at Santa Maria volcano, Guatemala, using an Unoccupied Aircraft System (UAS) to create topography data and orthophotos of the lava dome. This enabled us to track pixel-offsets and delineate the 2D displacement field, strain components, extrusion rate, and apparent lava viscosity. We find that the lava dome displays motions on two separate timescales, (i) slow radial expansion and growth of the dome and (ii) a narrow and fast-moving lava extrusion. Both processes also produced distinctive fracture sets detectable with surface motion, and high strain zones associated with thermal anomalies. Our results highlight that motion patterns at lava domes control the structural and thermal architecture, and different timescales should be considered to better characterize surface motions during dome growth to improve the assessment of volcanic hazards.
Article
The morphology of a silicic lava is created by the fluid dynamic conditions that operated during flow. Careful analysis of these features can thus be used to reconstruct emplacement processes. We used unoccupied aerial system and structure-from-motion photogrammetry techniques to collect centimeter-scale spatial resolution imagery of the surfaces of South Coulee and Obsidian Dome rhyolite lavas (Mono-Inyo Craters, USA). We supplement the newly acquired orthomosaics and digital elevation models with existing imagery of other Holocene rhyolite lavas from across the western USA, including Rock Mesa Dome (South Sister, OR), Newberry Flow (South Sister, OR), Obsidian Flow (Newberry, OR), Interlake Flow (Newberry, OR), and Banco Bonito Flow (Valles Caldera, NM). Although many morphologic features exist, we restrict our quantitative analyses to the recurrent ridges and blocks of loose rubble that are common to the flows. Ridge spacing and ridge vergence indicate the ridges are likely folds produced by compression during emplacement. Pressure ridge spacings range from 27 to 45 m at South Coulee and 18 to 34 m on Obsidian Dome. Spacing generally decreases with distance from the vent across both lavas. Ridge amplitudes range from 4 to 17 m at both lavas and show little correlation with distance from the vent. The vergence of the crest of the ridges in the flow interiors points back to the source vent, which provides strong evidence for endogenous flow and the backward rotation of folds produced by undertow of the underlying lava. Ridges near flow margins verge towards the flow front, demonstrating that exogenous flow becomes increasingly important at the point of advance. In both South Coulee and Obsidian Dome block sizes are largest near the vent, and gradually decrease towards the flow front. The gradual decrease in block size with increasing distance from the vent likely reflects decreasing effusion rates from the conduit. We interpret our high-resolution field measurements under the lens of analytical solutions to fluid dynamic models to estimate emplacement timescales and associated rates. We calculate relatively abbreviated eruptive timescales ranging from 1 month to <2 years. Such values predict eruptive fluxes <135 m³ s⁻¹ and velocities <100 m day⁻¹, providing helpful criterion for volcanic monitoring or hazard forecasting efforts.
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Vulcano Fossa's fumarole field (Italy) has been active for more than a century and has become a well‐studied benchmark for fumarolic degassing, often being considered the “model” hydrothermal system. Satellite thermal monitoring is increasingly being used to monitor such systems, so we here use Vulcano to test a new method for assessing heat flux at such systems. Our methodology involves converting ground‐based vent temperature measurements to heat fluxes emitted by the fumaroles, with the diffuse heat flux obtained from satellite‐sensor (in our case Advanced Spaceborne Thermal Emission and Reflection Radiometer) data. While diffuse heat losses were typically 9 MW, vent heat losses were 1 MW. The average total flux of 10 MW over the 19‐year period of study places Vulcano in the top 20 most active hydrothermal systems globally. This work highlights the value of high spatial resolution infrared satellite data in building thermal inventories for persistently active hydrothermal systems.
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Volcanic gas emissions are intimately linked to the dynamics of magma ascent and outgassing, and, on geological timescales, constitute an important source of volatiles to the Earth's atmosphere. Measurements of gas composition and flux are therefore critical to both volcano monitoring and to determining the contribution of volcanoes to global geochemical cycles. However, significant gaps remain in our global inventories of volcanic emissions, (particularly for CO2, which requires proximal sampling of a concentrated plume) for those volcanoes where the near‐vent region is hazardous or inaccessible. Unmanned Aerial Systems (UAS) provide a robust and effective solution to proximal sampling of dense volcanic plumes in extreme volcanic environments. Here, we present gas compositional data acquired using a gas sensor payload aboard a UAS flown at Volcán Villarrica, Chile. We compare UAS‐derived gas timeseries to simultaneous crater rim multi‐GAS data and UV camera imagery to investigate early plume evolution. SO2 concentrations measured in the young proximal plume exhibit periodic variations that are well‐correlated with the concentrations of other species. By combining molar gas ratios (CO2/SO2 = 1.48–1.68, H2O/SO2 = 67–75 and H2O/CO2 = 45–51) with the SO2 flux (142 ± 17 t/day) from UV camera images, we derive CO2 and H2O fluxes of ~150 t/day and ~2850 t/day, respectively. We observe good agreement between time‐averaged molar gas ratios obtained from simultaneous UAS‐ and ground‐based multi‐GAS acquisitions. However, the UAS measurements made in the young, less diluted plume reveal additional short‐term periodic structure that reflects active degassing through discrete, audible gas exhalations.
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Lava flow simulations help to better understand volcanic hazards and may assist emergency preparedness at active volcanoes. We demonstrate that at Fogo Volcano, Cabo Verde, such simulations can explain the 2014–2015 lava flow crisis and therefore provide a valuable base to better prepare for the next inevitable eruption. We conducted topographic mapping in the field and a satellite-based remote sensing analysis. We produced the first topographic model of the 2014–2015 lava flow from combined terrestrial laser scanner (TLS) and photogrammetric data. This high-resolution topographic information facilitates lava flow volume estimates of 43.7 ± 5.2 × 10⁶ m³ from the vertical difference between pre- and posteruptive topographies. Both the pre-eruptive and updated digital elevation models (DEMs) serve as the fundamental input data for lava flow simulations using the well-established DOWNFLOW algorithm. Based on thousands of simulations, we assess the lava flow hazard before and after the 2014–2015 eruption. We find that, although the lava flow hazard has changed significantly, it remains high at the locations of two villages that were destroyed during this eruption. This result is of particular importance as villagers have already started to rebuild the settlements. We also analysed satellite radar imagery acquired by the German TerraSAR-X (TSX) satellite to map lava flow emplacement over time. We obtain the lava flow boundaries every 6 to 11 days during the eruption, which assists the interpretation and evaluation of the lava flow model performance. Our results highlight the fact that lava flow hazards change as a result of modifications of the local topography due to lava flow emplacement. This implies the need for up-to-date topographic information in order to assess lava flow hazards. We also emphasize that areas that were once overrun by lava flows are not necessarily safer, even if local lava flow thicknesses exceed the average lava flow thickness. Our observations will be important for the next eruption of Fogo Volcano and have implications for future lava flow crises and disaster response efforts at basaltic volcanoes elsewhere in the world.