Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p34a..03b&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P34A-03
Physics
5420 Impact Phenomena (Includes Cratering), 6225 Mars, 3210 Modeling
Scientific paper
We present a model for the emplacement of a single layer ejecta rampart deposit. The model assumes that the ejecta blanket and rampart were formed by a continuum surface flow beginning at or near the crater rim. There has been abundant evidence for this in the literature for many years and recent THEMIS and MOC imaging continue to support the validity of this assumption. We use this model to determine the basic physical processes necessary to form the distal ramparts in such craters. We find cylindrically symmetric solutions for the flow thickness and velocity of the advancing ejecta flow from volume and momentum conservation equations. The momentum equation has an inertial term and a frictional resistance term that is proportional to the local volumetric flow rate. Only a few basic physical processes are necessary to form sharp distal ramparts. First, there must be sufficient material to form a continuum overland flow. Then, the cylindrical geometry, the inertia of the flow, and local flow resistance combine naturally to form a distal rampart when volume conservation is imposed. We measured nine clearly expressed single layer ejecta deposits for craters with diameters of 3.4 to 17.0 km. The model provides estimates of the emplacement time, the shape of the radial flow depth profiles and the approximate width of the rampart. We find unexpectedly modest velocities of ~20 to 40 m s-1, maximum crater rim flow depths of 10 to 30 m, and emplacement durations of 10 to 80 minutes adequately explain the morphologies of selected rampart craters.
Baloga Stephen M.
Fagents Sarah A.
Mouginis-Mark Peter J.
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