Post by Giulia Magnarini, PhD candidate, Department of Earth Sciences, University College London, UK.
The availability of high resolution imagery of the surface of Mars from NASA’s Mars Reconnaissance Orbiter CTX and HiRISE cameras (NASA PDS) allow us to reconstruct fantastic 3D views of the martian topography using stereophotogrammetry technique. Digital terrain models (DTMs) are obtained using the difference in two images of the same target taken from different angles. In the process, orthoimages are generated and draped over the DTM. CTX stereo-derived DTMs have 20 m/px resolution; HiRISE stereo-derived DTMs have 1-2 m/px resolution. This technique is applied to the study of martian long runout landslides and it represents a powerful tool, as the 3D reconstruction allows detailed observations and morphometric analysis of these landforms and their morphological features (Images 1-3).
Image 1: Long runout landslide in Ganges Chasma, Valles Marineris, Mars. CTX stereo-derived DTM at the Mineral and Planetary Sciences division of the Natural History Museum in London. Vertical exaggeration 2x. Image pair: P20_008681_1722_XN_07S044W and P20_009037_1718_XN_08S044W.
Image 2: Three long runout landslides in North Aurorae Chaos, Mars. CTX stereo-derived DTM at the Mineral and Planetary Sciences division of the Natural History Museum in London. Vertical exaggeration 2x. Image pair: P07_003578_1757_XI_04S035W and G10_022091_1772_XI_02S035W.
Image 3: Long runout landslide in Shalbatana Valley, Mars. CTX stereo-derived DTM at the Mineral and Planetary Sciences division of the Natural History Museum in London. Vertical exaggeration 1.5x. Image pair: P02_001930_1834_XI_03N043W and P04_002431_1835_XI_03N043W (Image credit: Peter Grindrod). Inset: HiRISE stereo-derived DTM at the Mineral and Planetary Sciences division of the Natural History Museum in London. Vertical exaggeration 2x. Image pair: PSP_005965_1855_RED and ESP_011529_1855_RED (Image credit: Peter Grindrod).
Characterized by large volumes (> 106 m3), martian long runout landslides are able to travel for tens of kilometre, moving on nearly horizontal surfaces with velocities that can exceed 100 km/h. Numerous mechanisms have been proposed to explain their remarkable mobility: physical consequences of volume, geomorphological control on the runout path, and mechanisms responsible for the reduction of internal and basal friction. This long-lasting debate, yet to find agreement of geoscientists and physicists, can be summarized in three main questions: 1) to what extent fluids are important for the emplacement of these catastrophic landslides? (e.g., Lucchitta, 1979; McEwen, 1989; Collins and Melosh, 2003); 2) to what extent slope lithology and material present on valley floors play a role in facilitating the runout? (e.g., Erissman et al., 1977; De Blasio, 2011; Watkins et al., 2015; Mitchell et al., 2015); 3) to what extent the tectonic and structural settings predispose slope failures to evolve into long runout landslides?
Image 4: The impressive 63-km-long landslide in Coprates Chasma, in Valles Marineris, Mars. Vertical exaggeration 2x. The black&white image is a mosaic of 2 CTX image-pairs: B21_017688_1685_XN_11S067W and B22_018321_1685_XN_11S068W, P20_008906_1685_XN_11S067W and P22_009763_1690_XN_11S067W. The coloured image is a HiRISE stereo-derived DTM. Colour-coded DTM is laid on the orthoimage with 40% transparency. Image pair: PSP_008906_1685_RED and PSP_009763_1685_RED.
With the aid of high resolution DTMs and orthoimages, detailed morphometric analysis will help clarifying the relationship between the occurrence of morphological traits typical of martian long runout landslides, such as longitudinal ridges (Image 4) and their dynamic behaviour, in the attempt to link their morphology to the mechanisms involved during such catastrophic events.
Further Reading
Collins, G. S. and H. J. Melosh (2003), Acoustic fluidization and the extraordinary mobility of sturzstroms, JGR Solid Earth, 108(B10).
De Blasio, F. V. (2011), Landslides in Valles Marineris (Mars): A possible role of basal lubrication by sub-surface ice, Planetary Space Science, 59(13), 1384-1392.
Erismann, T. H et al. (1977), Fused Rock of Kofels (Tyrol) – Frictionite Generated by a Landslide, Tschermaks mineralogische und petrographische Mitteilungen, 24(1-2), 67-119.
Lucchitta, B. K. (1979), Landslides in Valles Marineris, Mars, JGR Solid Earth, 84, 8097-8113.
McEwen, A. S. (1989), Mobility of Large Rock Avalanches – Evidence from Valles Marineris, Mars, Geology, 17(12), 1111-1114.
Mitchell, T. M. et al. (2015), Catastrophic emplacement of giant landslides aided by thermal decomposition: Heart Mountain, Wyoming, Earth Planet Science Letters, 411, 199-207.
NASA Planetary Data System (PDS), http://pds-geosciences.wustl.edu.
Watkins, J. A. et al. (2015), Long-runout landslides and the long-lasting effects of early water activity on Mars, Geology, 43(2), 107-110.
Planetary Geomorphology Image of the Month 