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Rebecca Williams

Rebecca Williams Senior Research Scientist
Planetary Science Institute


Publications List | Curriculum Vitae | 2007 Research Report

The unifying objective of my research is to unravel the history of water on Mars through qualitative and quantitative characterization of landforms using image and topographic datasets. My investigations of martian geomorphology principally center on landscape evolution by surface runoff. These studies seek to constrain the relative timing, duration and magnitude of fluvial processes on Mars. Individual projects have examined these questions for large-scale features (outflow channels and valley networks) as well as small scale landforms (sub-kilometer fans and recently recognized inverted channel networks). My research builds upon field observations of terrestrial analogs to enhance the interpretation of remotely sensed data from Mars. Further details of recent and ongoing research are given below.

Investigation of Unique Fans within 'Mojave' Crater

High resolution Mars Orbiter Camera (MOC) images reveal unique, ~0.5 km scale fan-shaped landforms in a single, fresh-appearing crater that have morphologic characteristics similar to terrestrial alluvial fans (Williams et al. 2004a). These landforms may be evidence of recent (i.e. Amazonian) precipitation. Further, their unique occurrence has led to speculation that the formation of these landforms was related to the impact event that formed 'Mojave' Crater. Using Differential Global Positioning System (DGPS) owned by CEPS, high precision topographic measurements of comparably-sized terrestrial alluvial fans on Earth are being acquired to identify aspects of landform shape that are diagnostic of fan formation processes. Such criteria will enable a better understanding of the climatic conditions under which the 'Mojave' Crater fans formed and the relative timing of fan formation within the crater (Williams et al. 2005a).

Martian Inverted Ridge Networks

At several locations on Mars, bifurcating ridge networks covering areas of a few tens of square kilometers, comparable in scale to creek systems on Earth, are preserved within the martian stratigraphy (Williams et al. 2005b), (Williams and Edgett 2005)). The ridge networks are interpreted to be the former courses of streams that have been buried and exhumed resulting in the present day inverted topography surface expression. The drainage density of these ridge networks is an order of magnitude higher than typical martian valley networks and suggests long-lived surface runoff and supports formation via precipitation.

Late-stage Flow History in Kasei Valles, Mars

Within the southern branch of Kasei Valles are two inner channels that document the late-stage flow history of the largest outflow channel on Mars (Williams et al. 2004b). A mosaic of MOC images of the two channels reveals perched boulders and arcuate alcoves, attributes consistent with the interpretation that these channels were carved by a Newtonian fluid. The sharp, concave-up longitudinal profile shape is consistent with a system in quasi-equilibrium. Associated with these channels is a 'platy' meter-scale texture, perhaps a mudflow deposit related to waning floodwaters moving through the inner channels.

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