MER INVESTIGATIONS OF THE COLUMBIA HILLS: GEOMORPHOLOGY AND ROCK WEATHERING PROCESSES

The second phase of the MER Spirit mission, in Gusev crater, began when the rover entered the province of the Columbia Hills. The rover traveled over 3km to arrive at this destination. The Columbia Hills rise up to 90m above the basaltic plains that Spirit spent the first 5 months investigating. These plains appear to be impact gardened lava flows that have subsequently undergone aeolian reworking. The Columbia Hills are embayed by the plains and are therefore much older materials. The origin and composition of the Columbia Hills, as of this writing, are still unknown. Several possible origins have been considered: eroded and partially buried impact crater rim, central peak of former crater, volcanic construct, or remnant of a formerly extensive crater fill deposit. The slopes of the Hills are covered with boulders and outcroppings of rock appear to be present along the flanks. Heretofore previously unseen deep cavernous weathering (case hardening and core softening) of rocks was observed upon crossing the contact with the plains. This type of weathering typically involves groundwater and salts. Several of these rocks have unusual morphologies (pedestals or fingers projecting away from rock's center with terminal clumps) that are somewhat similar in appearance to rocks seen at Meridiani Planum. Immediate plans are to perform IDD work on outcrop material and then ascend the summit of Husband Hill, which is the highest peak in the Columbia Hills, and winter over here.