Mathematics – Logic
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p32b..02c&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P32B-02
Mathematics
Logic
5139 Transport Properties, 5470 Surface Materials And Properties, 5475 Tectonics (8149), 6225 Mars, 8120 Dynamics Of Lithosphere And Mantle: General
Scientific paper
Debris flow deposits formed by enormous landslides are common in the Valles Marineris canyons. Laser altimeter (MOLA) data from Mars Global Surveyor permit detailed studies of these deposits. MOLA pass 13088 crossed a large debris fan in Ganges Chasma at latitude 8.4 S, longitude 44.9 W. At this longitude the floor of Ganges Chasma is 5 km deeper than the south rim of the canyon. The deposit includes overlapping lobes from several other debris flows and reaches a maximum thickness of 450 m. The distal edge of the fan traveled about 44 km from its source in the southern wall of Ganges Chasma. This northern edge of the fan is abrupt with multiple lobes. The surface of the debris fan has ridges up to 100 m high. Using an average thickness of 250 m and the roughly circular shape of the fan, we estimate its volume exceeds 3E11 cubic meters. We estimate the runout efficiency by dividing the horizontal runout distance of the debris flow by the change in elevation from the source to the deposit (Iverson, R., Rev. of Geophysics, 35, 1997). Ideally these measurements are based on the center of mass of both the source zone and the deposit. On Earth, runout efficiencies of debris flows vary from about 2 to 25 and tend to increase with the flow volume. The Ganges Chasma deposit is 3 to 4 km lower than its source. Using a center-of-mass runout distance of 35 km, the debris flow had a runout efficiency in the range from 9 to 12. The volume of the Ganges Chasma fan is about 100 times that of the Osceola mudflow at Mount Rainier, WA, one of the largest well-documented debris flows on Earth, which had an estimated runout efficiency of 25 (Iverson, 1997). Therefore, the relatively low runout efficiency of the voluminous Ganges Chasma fan suggests that the landslide debris did not contain a large fraction of frozen volatiles. Such volatiles would have been liquified or vaporized by frictional heating during the slide, enhancing the runout distance. We suggest that runout efficiencies be calculated for the small debris fans formed by geologically recent gullies on steep slopes at high southern latitudes on Mars. Data of this kind could help to better understand the genesis of the gullies and their associated deposits.
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