SIMULATIONS OF CRATERING AND EROSION ON THE MARTIAN HIGHLANDS
The simulation domain is 256x256 scaled to .4 km/cell, so that the simulated
area is about 102x102 km. Both the vertical and lateral boundaries are
periodic, so that the left side is (computationally) contiguous with the right
side, and the top with the bottom. This is done to avoid needing to
specify external boundary conditions. Simulations start from a simulated
saturated cratered surface with craters from 1 to 50 km in size.
Simulated processes include weathering, creep, threshold mass wasting, fluvial
detachment, sediment transport and fluvial deposition. Some simulations
include groundwater sapping.
In this simulation the initial weathered regolith is initially 1 m thick, and when mass wasting or fluvial erosion exposes bedrock, the erodibility drops by a factor of 10. There is no critical shear stress for fluvial erosion, and creep rates are low enough to be ineffectual. However, mass wasting increases without limit as regolith slopes approach a gradient of 0.8 and when bedrock slopes approach a gradient of 2.7. These simulations employ a "desert" hydrology such that no ponded water is allowed (water "evaporates" when it reaches enclosed depressions). In the first few simulations fluvial runoff is "Hortonian" overland flow due to excess of ranfall rate over infiltration capacity and runoff yield is assumed to be spatially uniform.
In this simulation the
central area is higher than the top and bottom boundaries. The north and
south borders become alluviated by fans. Fans also established in the
interiors of larger craters. Notice that deep, transient valleys develop
when an upland basin becomes breached and dissected. Erosion and valley
development erode the exterior rim of large craters until they often become
nearly as steep as the interior crater wall. Note that the alluviated
floors of individual craters or groups of craters on upland areas can become
high plateaus that are primarily eroded around their edges -- often the
original crater rims have been removed, so that the upland flats seem
"inexplicable".