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Rui Quartau - One of the best experts on this subject based on the ideXlab platform.
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imprints of volcanic erosional depositional tectonic and Mass Wasting processes in the morphology of santa maria insular shelf azores
Marine Geology, 2020Co-Authors: Alessandro Ricchi, Daniele Casalbore, Rui Quartau, Ricardo S Ramalho, Claudia Romagnoli, Zhongwei ZhaoAbstract:Abstract The present-day morphology of volcanic island shelves is the result of several factors, namely the original shape and structure of the volcanic edifice, the nature and age of the materials that compose its flanks, and the erosional, volcanic, tectonic and sedimentary processes that acted to form these shelves. By combining detailed seafloor mapping with onshore studies it is possible to gain a unique insight onto the evolution of volcanic island edifices and the processes that helped to shape their shelves. Here we look at Santa Maria Island in the Azores Archipelago, which is a 6 Ma old ocean-island volcano surrounded by a 135 km2 shelf, characterized by an history of subsidence since its formation c. 6 Ma ago, followed by uplift from 3.5 Ma onwards. By analyzing the geomorphic parameters of the insular shelf (such as the shelf width and the erosive edge depth), the island's history of vertical movements, and by relating the morphology of the outcrops found on the shelf with those onshore, we contribute to a better knowledge of the evolutionary history of Santa Maria with particular focus on its earlier stages of growth. We infer that the outer part of the northern shelf is carved on units older than the oldest volcanic sequences exposed on land; the western and southern shelves are almost entirely carved in the products of the oldest shield volcano (Anjos Volcanic Complex), whilst the eastern shelf is the youngest in formation, being related to units of the Pico Alto volcanic complex. We also discuss the distribution of sediments on the shelf. High wave energy concomitant with sea level drops contributed to the erosion and transport of older sequences offshore, which were ultimately lost to the slopes of the island, resulting in a shelf that is sediment-stripped for the most part. Presently, wide shelves further contribute to wave-energy dissipation, resulting in a significantly diminished sediment production. The shelf edges around Santa Maria exhibit several erosive scars, interpreted as the head of a submarine drainage network carved on the slopes of the island. On the western, southern and eastern shelves, these Mass-Wasting features are mostly controlled by tectonics since the extension of faults can be followed from onshore to the shelf edge. On the northern shelf Mass-Wasting appears to be mostly correlated with presence of unstable sediments on the shelf edge that triggered landsliding. Overall, this work shows how detailed mapping of the shelves surrounding old volcanic islands can still provide important complementary information about the evolution of these islands, which could not be acquired solely by the study of their subaerial and deeper submarine parts.
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volcanic tectonic and Mass Wasting processes offshore terceira island azores revealed by high resolution seafloor mapping
Bulletin of Volcanology, 2015Co-Authors: Daniele Casalbore, C Romagnoli, Adriano Pimentel, Rui Quartau, David Casas, Gemma Ercilla, Ana Hipolito, A Sposato, F L ChiocciAbstract:Terceira Island, in the Azores Archipelago, lies at the intersection of four submarine volcanic ridges. New high-resolution bathymetric and seismic reflection data have been used to analyze the main volcanic, tectonic and Mass-Wasting features of the island offshore. Volcanic features such as linear volcanic centers, and pointy and flat-topped cones are mainly concentrated on the narrow western and north-western ridges, characterized by an overall rugged morphology. Fault scarps dominate mainly the broad eastern and south-eastern ridges, which are characterized by an overall smooth and terrace-like morphology. On the eastern ridge, faults form a series of horsts and grabens related to the onshore Lajes Graben. The strikes of the fault scarps, linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends, WNW–ESE and NNW–SSE, consistent with the main tectonic structures observed on the Azores Plateau. In contrast, a large variability of strike was observed in inter-ridge areas, reflecting the relative importance of regional and local stresses in producing these structures. Mass-Wasting features are subordinate and mostly represented by hundred meter-wide scars that indent the edge of the insular shelf surrounding the island, apart from two large, deeper scars identified on the southern steep flank of the western ridge. Finally, the remarkable morpho-structural differences between the western and eastern ridges are discussed in the framework of the evolution of the Terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution.
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morphology of the faial island shelf azores the interplay between volcanic erosional depositional tectonic and Mass Wasting processes
Geochemistry Geophysics Geosystems, 2012Co-Authors: Rui Quartau, Fernando Tempera, Neil C Mitchell, L M Pinheiro, Henrique Duarte, P O Brito, C R Bates, J H MonteiroAbstract:[1] The extents of volcanic island shelves result from surf erosion, which enlarges them, and volcanic progradation, which reduces them. However, Mass-Wasting, tectonics and sediment deposition also contribute to their morphology. In order to assess the relative significance of these various processes, we have mapped in detail Faial Island's shelf in the Azores archipelago based on interpretation of geophysical and geological data. The nearshore substrates of the island, down to 30–50 m depth, are rocky and covered by volcaniclastic boulder deposits formed by surf action on now-submerged lava flows. Below those depths, sandy and gravel volcaniclastic beds dominate, building clinoforms up to the shelf edge. In some sectors of the coast, prograding lava has narrowed the shelf, but, in contrast to nearby Pico Island, we find fewer submarine-emplaced lavas on the shelf. In this island, we interpret the distance between the coastline and the shelf edge as almost entirely a result of a straightforward competition between surf erosion and lava progradation, in which erosion dominates. Therefore shelf width can be used as a proxy for coastline age as well as for wave energy exposure. The stratigraphy of shelf deposits in boomer seismic data is examined in detail to assess the roles of different sediment sources, accommodation space and wave exposure in creating these deposits. We also show evidence of Mass-Wasting at the shelf edge and discuss the possible origins of slope instability. Finally, we discuss the contributing role of tectonics for the development of the shelf.
Daniele Casalbore - One of the best experts on this subject based on the ideXlab platform.
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imprints of volcanic erosional depositional tectonic and Mass Wasting processes in the morphology of santa maria insular shelf azores
Marine Geology, 2020Co-Authors: Alessandro Ricchi, Daniele Casalbore, Rui Quartau, Ricardo S Ramalho, Claudia Romagnoli, Zhongwei ZhaoAbstract:Abstract The present-day morphology of volcanic island shelves is the result of several factors, namely the original shape and structure of the volcanic edifice, the nature and age of the materials that compose its flanks, and the erosional, volcanic, tectonic and sedimentary processes that acted to form these shelves. By combining detailed seafloor mapping with onshore studies it is possible to gain a unique insight onto the evolution of volcanic island edifices and the processes that helped to shape their shelves. Here we look at Santa Maria Island in the Azores Archipelago, which is a 6 Ma old ocean-island volcano surrounded by a 135 km2 shelf, characterized by an history of subsidence since its formation c. 6 Ma ago, followed by uplift from 3.5 Ma onwards. By analyzing the geomorphic parameters of the insular shelf (such as the shelf width and the erosive edge depth), the island's history of vertical movements, and by relating the morphology of the outcrops found on the shelf with those onshore, we contribute to a better knowledge of the evolutionary history of Santa Maria with particular focus on its earlier stages of growth. We infer that the outer part of the northern shelf is carved on units older than the oldest volcanic sequences exposed on land; the western and southern shelves are almost entirely carved in the products of the oldest shield volcano (Anjos Volcanic Complex), whilst the eastern shelf is the youngest in formation, being related to units of the Pico Alto volcanic complex. We also discuss the distribution of sediments on the shelf. High wave energy concomitant with sea level drops contributed to the erosion and transport of older sequences offshore, which were ultimately lost to the slopes of the island, resulting in a shelf that is sediment-stripped for the most part. Presently, wide shelves further contribute to wave-energy dissipation, resulting in a significantly diminished sediment production. The shelf edges around Santa Maria exhibit several erosive scars, interpreted as the head of a submarine drainage network carved on the slopes of the island. On the western, southern and eastern shelves, these Mass-Wasting features are mostly controlled by tectonics since the extension of faults can be followed from onshore to the shelf edge. On the northern shelf Mass-Wasting appears to be mostly correlated with presence of unstable sediments on the shelf edge that triggered landsliding. Overall, this work shows how detailed mapping of the shelves surrounding old volcanic islands can still provide important complementary information about the evolution of these islands, which could not be acquired solely by the study of their subaerial and deeper submarine parts.
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volcanic tectonic and Mass Wasting processes offshore terceira island azores revealed by high resolution seafloor mapping
Bulletin of Volcanology, 2015Co-Authors: Daniele Casalbore, C Romagnoli, Adriano Pimentel, Rui Quartau, David Casas, Gemma Ercilla, Ana Hipolito, A Sposato, F L ChiocciAbstract:Terceira Island, in the Azores Archipelago, lies at the intersection of four submarine volcanic ridges. New high-resolution bathymetric and seismic reflection data have been used to analyze the main volcanic, tectonic and Mass-Wasting features of the island offshore. Volcanic features such as linear volcanic centers, and pointy and flat-topped cones are mainly concentrated on the narrow western and north-western ridges, characterized by an overall rugged morphology. Fault scarps dominate mainly the broad eastern and south-eastern ridges, which are characterized by an overall smooth and terrace-like morphology. On the eastern ridge, faults form a series of horsts and grabens related to the onshore Lajes Graben. The strikes of the fault scarps, linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends, WNW–ESE and NNW–SSE, consistent with the main tectonic structures observed on the Azores Plateau. In contrast, a large variability of strike was observed in inter-ridge areas, reflecting the relative importance of regional and local stresses in producing these structures. Mass-Wasting features are subordinate and mostly represented by hundred meter-wide scars that indent the edge of the insular shelf surrounding the island, apart from two large, deeper scars identified on the southern steep flank of the western ridge. Finally, the remarkable morpho-structural differences between the western and eastern ridges are discussed in the framework of the evolution of the Terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution.
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Mass Wasting features on the submarine flanks of ventotene volcanic edifice tyrrhenian sea italy
2014Co-Authors: Daniele Casalbore, A Sposato, Alessandro Bosman, Eleonora Martorelli, F L ChiocciAbstract:High-resolution multibeam bathymetry acquired around Ventotene and S. Stefano islands (eastern Pontine Archipelago, Italy) enabled us to map main Mass Wasting features affecting their submarine portions. Large-scale instability morphological features are absent (apart from a 4 × 2.5 km caldera in the western sector), whereas 126 landslide scars of 100-m of length scale were identified between 130 and 1,150 m of water depth (wd). Two main groups of scars can be distinguished: the first one affects the edge of the insular shelf between 130 and 260 m wd. The second group affects the lower slope and surrounding basins, representing cases of retrogressive failure at the heads of channelized features. The different morphological relief of the scars coupled with the recognition of crescent-shaped bedforms made it possible to distinguish two Mass-Wasting/erosive stages and consequently to map the more active sectors of the edifice. The future evolution of the Mass Wasting processes will produce the enlargement of erosive sectors with possible formation of large channels, which will carve wide sectors of the edifice, as suggested by available geological constraints and by comparison with the nearby and older western sector of the Pontine archipelago, where a more mature organization of Mass Wasting processes is observed. The present study can provide useful insights for hazard assessment and future planning of risk mitigation in such islands that are densely populated and touristically exploited during the summer months.
Menglong Hsieh - One of the best experts on this subject based on the ideXlab platform.
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a Mass Wasting dominated quaternary mountain range the coastal range in eastern taiwan
Quaternary Science Reviews, 2017Co-Authors: Menglong Hsieh, Alan G Hogg, Shengrong Song, Suchen Kang, Chunyen ChouAbstract:Abstract Fluvial bedrock incision, which creates topographic relief and controls hillslope development, has been considered the key medium linking denudation and tectonic uplift of unglaciated mountains. This article, however, shows a different scenario from the Coastal Range in eastern Taiwan. This range, with the steepness inherited from pre-orogenic volcanoes, has been subject to Mass Wasting even before its emergence above sea level no earlier than Middle Pleistocene. Numerous terraced alluvial fans/fan deltas record the ancient Mass movements of the range, including rock avalanches. Multiple radiocarbon dates 1 km 2 . Alluvial terraces are typically exhibited close to the source ridges of Mass movements, and strath terraces along the downstream parts of rivers. Both were created when enormous sediment supply had exceeded or matched the prevailing river transport capacity. This process, along with the protection by giant boulders from Mass movement, disturbed the long-term incision trend of rivers in response to tectonic uplift. As a result, the observed Holocene bedrock incision at most sites has not kept pace with the tectonic uplift. The spatial contrast in Mass-Wasting histories further accounts for the great diversity of the terrace sequences, even in areas with similar tectonic and base-level conditions.
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late quaternary Mass Wasting records in the actively uplifting pa chang catchment southwestern taiwan
Geomorphology, 2014Co-Authors: Menglong Hsieh, Shyhjeng Chyi, Suchen Kang, Kuo En Ching, Chunyen ChouAbstract:Abstract Although dominated by erosion over long term, the tectonically active mountains of Taiwan commonly contain thick landslide and debris-flow gravels capping hillslopes or forming alluvial terraces. These deposits and their associated landforms serve to study ancient Mass-Wasting histories and their controls on fluvial processes. This study focuses on the Pa-chang River draining the 50 mm yr− 1) are detected further downstream after the recent gravel mining. The fact that the obtained bedrock incision rates and patterns are decoupled with the tectonic uplift advises caution in using short-term erosion data to interpret the tectonics of the Taiwan's mountains.
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early holocene catastrophic Mass Wasting event and fan delta development on the hua tung coast eastern taiwan
Geomorphology, 2011Co-Authors: Menglong Hsieh, Pingmei Liew, Huawen ChenAbstract:Abstract Landslides and debris flows rarely occurred during historical times in the tectonically active Coastal Range of eastern Taiwan. This topographic stability, however, contrasts greatly with the widespread existence of terraced alluvial fans and fan-deltas on the Hua-tung coast which fringes the range. This study focuses on the two largest fan–terrace systems on the Hua-tung coast, both of which consist of alluvial fans (plane-view areas up to 8 km 2 ) larger than their contributing catchments. Stratigraphic data show that both systems were in sandy, wave-dominated settings during de-glacial times. The systems were then disturbed by a catastrophic landslide/debris-flow event (or events), which brought enormous amounts of gravel (Facies Gm) into the systems, deforming previously-deposited marine sands (Facies Sm) and shallowing the seafloor. The combined Gm/Sm complex yields multiple radiocarbon dates ranging from 11.3 to 8.3 ka cal BP, with a cluster around 8.6 ka cal BP. This Mass-Wasting event has been unique since the emergence of its contributing catchment 0.2–0.3 Ma ago. The low frequency of such an event could reflect the great resistance of rock Mass in the source areas to weathering and erosion. The common blockage of valley floors by giant-boulder piles, which limits channel incision and sediment transport, could also increase the apparent stability of the mountain. The trigger of landslides in the Coastal Range has been linked to large earthquakes. Additionally, we propose that the great magnitude and duration of the observed early Holocene event were caused by the contemporaneous prolonged rainfall (and/or high frequency of typhoons) associated with the East Asian summer monsoon maximum.
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late quaternary Mass Wasting records and formation of fan terraces in the chen yeo lan and lao nung catchments central southern taiwan
Quaternary Science Reviews, 2010Co-Authors: Menglong Hsieh, Shyhjeng ChyiAbstract:Abstract Development of fan terraces in incision-dominated river settings documents episodic increases of sediment supply from upland catchments. In the non-glaciated, active mountains of Taiwan, such increases in sediment supply result typically from increases in landslide/debris flow activity. Studying fan terraces, therefore, helps understand the history and nature of Mass-Wasting processes eroding the mountains. This study explores fan-terrace successions developed at tributary mouths of the Chen-yeo-lan and Lao-nung Rivers in central-southern Taiwan. Judging from the spatial variations of sizes, heights, sequences and sedimentation of the fan terraces, the magnitude and frequency of Mass-Wasting activities appear to vary from tributary catchment to catchment. Two types of tributary catchment are differentiated, which can be located in close proximity to each other. One has been subject to extremely large but infrequent Mass-Wasting events, as a result of which high and/or large fan terraces with 100–200 m thick debris-flow/fluvial gravels have been formed. Seven examples of this type of fan terrace have yielded radiocarbon dates of >40 ka, ∼18.4 ka, ∼13.9 ka, 8.9–9.5 ka, 3.9–4.8 ka, ∼3.3 ka, and ∼1.4 ka in age. With the availability of multiple dates, this type of fan terrace can be shown to have been created in no more than 1000 years, from the aggradation of thick gravel sequences to subsequent incision. The second type of catchment has been subject to relatively minor but frequent Mass-Wasting events. Due to repeated incision after each such event, the resultant fan terraces are relatively low and limited in size but have formed over lengthy periods. Although located in the same geological and geomorphic setting, the dated fan-forming Mass-Wasting events in the Chen-yeo-lan catchment do not appear to have occurred synchronously with those in the Lao-nung catchment. Nor could the succession of these events, or their origins, be clearly linked to known paleo-climate data. These findings highlight the importance of internal factors (e.g., rock-Mass strength) in determining the timing, magnitude, and frequency of Mass-Wasting events in the studied mountains, which are subject to active rock uplift, highly active seismicity, and intense rainfall.
Christian Hubscher - One of the best experts on this subject based on the ideXlab platform.
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semi automated bathymetric spectral decomposition delineates the impact of Mass Wasting on the morphological evolution of the continental slope offshore israel
Basin Research, 2020Co-Authors: Omri Gadol, Christian Hubscher, Gideon Tibor, Uri Ten S Brink, John K Hall, Gavrielle Grovesgidney, Gideon Baram, Yizhaq MakovskyAbstract:[The southeastern mediterranean continental slope bathymetry is impacted by interleaved imprints of Mass transport processes. These are delineated, classified and mapped through semi‐automatic bathymetric spectral decomposition, appraising their role in sediments bypassing and maintenance of a long‐term shelf‐to‐basin equilibrium profile. , Abstract Understanding continental‐slope morphological evolution is essential for predicting basin deposition. However, separating the imprints and chronology of different seafloor shaping processes is difficult. This study explores the utility of bathymetric spectral decomposition for separating and characterizing the variety of interleaved seafloor imprints of Mass Wasting, and clarifying their role in the morphological evolution of the southeastern Mediterranean Sea passive‐margin slope. Bathymetric spectral decomposition, integrated with interpretation of seismic profiles, highlights the long‐term shape of the slope and separates the observed Mass transport elements into several genetic groups: (1) a series of ~25 km wide, now‐buried slide scars and lobes; (2) slope‐parallel bathymetric scarps representing shallow faults; (3) slope‐perpendicular, open slope slide scars; (4) bathymetric roughness representing debris lobes; (5) slope‐confined gullies. Our results provide a multi‐scale view of the interplay between sediment transport, Mass transport and shallow faulting in the evolution of the slope morphology. The base of the slope and focused disturbances are controlled by ~1 km deep salt retreat, and mimic the Messinian base of slope. The top of the open‐slope is delimited by faults, accommodating internal collapse of the margin. The now‐buried slides were slope‐confined and presumably cohesive, and mostly nucleated along the upper‐slope faults. Sediment accumulations, infilling the now‐buried scars, generated more recent open‐slope slides. These latter slides transported ~10 km3 of sediments, depositing a significant fraction (~3 m in average) of the sediments along the base of the studied slope during the past < 50 ka. South to north decrease in the volume of the open‐slope slides highlight their role in counterbalancing the northwards diminishing sediment supply and helping to maintain a long‐term steady‐state bathymetric profile. The latest phase slope‐confined gullies were presumably created by channelling of bottom currents into slide‐scar depressions, possibly establishing incipient canyon headword erosion.]
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seismo stratigraphic evidences for deep base level control on middle to late pleistocene drift evolution and Mass Wasting along southern levant continental slope eastern mediterranean
Marine and Petroleum Geology, 2016Co-Authors: Christian Hubscher, Christian Betzler, Sonke ReicheAbstract:Abstract Since early Pliocene, a counterclockwise surface gyre transported Nile derived silt and clay northeastwards along the Levant coast, where a basinward prograding plastered drift emerged. Based on high-resolution seismic reflection data we develop a middle to late Pleistocene sequence stratigraphic scheme for this plastered drift. For creating stacked sections of the seismic data we used the common reflection surface (CRS) stack technology which enhanced lateral reflection continuity and visibility of deep reflections. The shelf comprises stratigraphic sequences which show classical, systems tract like stacking patterns of sea level controlled sequences such as offlapping forced regression deposits or diachronous ravinement surfaces which formed during base level rise. On the slope, base level was periodically located well below the wave base and thus rather controlled by hydrodynamics, presumably by high-velocity contour currents. Hence, the term ‘deep base level’ is introduced. The deep base level controlled especially down and backstepping slope deposits. This example shows that care has to be taken when interpreting subsurface data containing typical systems tract like seismic sequences, since such geometries do not necessarily imply shallow water deposition of the sediments. A chronostratigraphic analysis based on the seismic stratigraphy indicates that base level fluctuations were related to eccentricity driven glacio-eustatic fluctuations. Periodic Mass Wasting, facilitated by foreset over-steepening and possibly triggered by salt tectonics or erosion by the contour current occurred during late base level fall or early base level rise.
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southwest mallorca island a cool water carbonate margin dominated by drift deposition associated with giant Mass Wasting
Marine Geology, 2012Co-Authors: Thomas Ludmann, Christian Betzler, S Wiggershaus, Christian HubscherAbstract:Abstract By means of new high-resolution Parasound, multi-channel reflection seismic and multibeam swath bathymetry data, we provide new insight into the sedimentation processes at the margin of a cool-water carbonate ramp system off southwestern Mallorca Island, western Mediterranean Sea. Here, we mapped 7 depositional units which we tied to the Messinian unconformity. The oldest units (1–3) are deposited from late Messinian to late Pliocene during phases of extreme sea-level fluctuations. 2.4 Ma ago with the global climate cooling, when the estuarine water Mass circulation switched into an anti-estuarine pattern in the Mediterranean Sea and sea-level highstands reached the today level, bottom currents started to shape the distal deposits of the cool-water carbonate system off southwestern Mallorca, represented by depositional units 4–7. Although, sediment supply from the carbonate shelf to the slope is low due to the insignificant input of terrigenous clastics and slow reef growth, slope sediments reach thicknesses > 140 m. Our study displays that the accumulation of sediments at the southwestern insular margin was mainly controlled by long-lived bottom currents and giant submarine landslides. The bottom currents formed elongated mounded drifts that contemporaneously developed in alongslope and upslope direction. They are probably controlled by an isobath-parallel bottom current in a present water depth of 350–550 m which we associate with the Levantine Intermediate Water (LIW); and an upslope current acting in 250–600 m associated with the Algerian mesoscale gyres that enter the Balearic straits from SE. Several scarps at the present sea-floor indicate the predominance of slope failures in the study area. Additionally, Mass transport deposits occur basinwards in almost all depositional units. Accordingly, giant Mass Wasting events took place from the Pliocene into recent times. Locally, above the alongslope drift a field of sediment waves occurs in a water depth of 170–310 m. They are oriented slightly oblique to the contour lines with their steep flank facing upslope, showing wavelengths of 400–800 m and heights of 10–15 m. We suggest that the waves migrate in upslope direction perpendicular to the main isobath-parallel flow. Furthermore, the results of this study indicate that sea-level fluctuations have only a minor influence on drift deposition; instead submarine landslides caused the creation of new drift units. They significantly altered the relief of the sea-floor and thereby initiate the realignment of the prevailing current pattern. The fault scarps and detachment surfaces left behind were the nucleolus for the development of new drift units.
Ralf Jaumann - One of the best experts on this subject based on the ideXlab platform.
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the coriolis effect on Mass Wasting during the rheasilvia impact on asteroid vesta
Geophysical Research Letters, 2016Co-Authors: Katharina A Otto, Ralf Jaumann, Katrin Krohn, Frank Spahn, C A Raymond, C T RussellAbstract:We investigate the influence of the Coriolis force on Mass motion related to the Rheasilvia impact on asteroid Vesta. Observations by the NASA Dawn mission revealed a pattern of curved radial ridges, which are related to Coriolis-deflected Mass-Wasting during the initial modification stage of the crater. Utilizing the projected curvature of the Mass-Wasting trajectories, we developed a method that enabled investigation of the initial Mass Wasting of the Rheasilvia impact by observational means. We demonstrate that the Coriolis force can strongly affect the crater formation processes on rapidly rotating objects, and we derive the material's velocities (28.9 +/- 22.5 m/s), viscosities (1.5-9.0 × 106 Pa s) and coefficients of friction (0.02-0.81) during the impact modification stage. The duration of the impact modification stage could be estimated to (1.1 +/- 0.5) h. By analyzing the velocity distribution with respect to the topography, we deduce that the Rheasilvia impactor hit a heterogeneous target and that the initial crater walls were significantly steeper during the modification stage.
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Mass Wasting features and processes in vesta s south polar basin rheasilvia
Journal of Geophysical Research, 2013Co-Authors: K Otto, Ralf Jaumann, Katrin Krohn, Klausdieter Matz, Frank Preusker, Thomas Roatsch, Paul M Schenk, Frank Scholten, K StephanAbstract:[1] The Rheasilvia crater is Vesta's largest impact basin. It is a 500 km diameter complex crater centered near the south pole and overlying the 400 km diameter impact basin Veneneia. Using Framing Camera (FC) data from the Dawn spacecraft's Low Altitude Mapping Orbit (20 m/pixel) and a digital terrain model derived from High Altitude Mapping Orbit stereo data, we identified various Mass-Wasting features within the south polar region. These features include intra-crater Mass movements, flow-like and creep-like structures, slumping areas, landslides, and curved radial and concentric ridges. Intra-crater Mass-Wasting features are represented by lobate slides, talus material, dark patches on the crater wall, spurs along the crater rim and boulders. Slumping areas develop in compact material, whereas landslides form in relatively loose material. Both may be triggered by seismic shaking induced by impacts. Intra-crater Mass Wasting and slid and slumped materials are homogeneously distributed throughout the basin. Slumping and sliding processes have contributed most efficiently to basin degradation. Flow-like and creep-like features originate from granular material and cluster between 0°E and 90°E, an area exposing shocked and fractured material from the Rheasilvia impact event. The radial curved ridges are likely to be remnants of the early Rheasilvia collapse process, when radially moving Masses were deflected by the Coriolis Effect. The concentric ridges are artifacts from the crater rim collapse. Curved ridges at the intersection of Rheasilvia and Veneneia, and on Rheasilvia's central peak, may also have been influenced by the Rheasilvia basin relaxation process, and an oblique impact, respectively.