Debris-covered piedmont glaciers along the northwest flank of the Olympus Mons scarp: Evidence for low-latitude ice accumulation during the Late Amazonian of Mars

We use Viking and new MGS and Odyssey data to characterize the lobate deposits superimposed on aureole deposits along the west and northwest flanks of Olympus Mons, Mars. These features have previously been interpreted variously as landslide, pyroclastic, lava flow or glacial features on the basis of Viking images. The advent of multiple high-resolution image and topography data sets from recent spacecraft missions allow us to revisit these features and assess their origins. On the basis of these new data, we interpret these features as glacial deposits and the remnants of cold-based debris-covered glaciers that underwent multiple episodes of advance and retreat, occasionally interacting with extrusive volcanism from higher on the slopes of Olympus Mons. We subdivide the deposits into fifteen distinctive lobes. Typical lobes begin at a theater-like alcove in the escarpment at the base of Olympus Mons, interpreted to be former ice-accumulation zones, and extend outward as a tongue-shaped or fan-shaped deposit. The surface of a typical lobe contains (moving outward from the basal escarpment): a chaotic facies of disorganized hillocks, interpreted as sublimation till in the accumulation zone; arcuate-ridged facies characterized by regular, subparallel ridges and interpreted as the ridges of surface debris formed by the flow of underlying ice; and marginal ridges interpreted as local terminal moraines. Several lobes also contain a hummocky facies toward their margins that is interpreted as a distinctive type of sublimation till shaped by structural dislocations and preferential loss of ice. Blocky units are found extending from the escarpment onto several lobes; these units are interpreted as evidence of lava-ice interaction and imply that ice was present at a time of eruptive volcanic activity higher on the slopes of Olympus Mons. Other than minor channel-like features in association with lava-ice interactions, we find no evidence for the flow of liquid water in association with these lobate features that might suggest: (1) near-surface groundwater as a source for ice in the alcoves in the lobe source region at the base of the scarp, or (2) basal melting and drainage emanating from the lobes that might indicate wet-based glacial conditions. Instead, the array of features is consistent with cold-based glacial processes. The glacial interpretations outlined here are consistent with recent geological evidence for low-latitude ice-rich features at similar positions on the Tharsis Montes as well as with orbital dynamic and climate models indicating extensive snow and ice accumulation associated with episodes of increased obliquity during the Late Amazonian period of the history of Mars.