Recent glaciation at high elevations on Arsia Mons, Mars: Implications for the formation and evolution of large tropical mountain glaciers

Abstract

[1] The $166,000 km 2 fan-shaped deposit at Arsia Mons contains three characteristic facies (ridged, knobby, and smooth), which are interpreted as the depositional remains of a cold-based glacier that was present on the west-northwestern flanks in the Late Amazonian period of Mars history. Here, we consider several high-elevation graben on the western flank of Arsia Mons that are interpreted as the source regions for late-stage, cold-based glaciers that overflowed graben walls, advanced tens to hundreds of kilometers downslope, experienced subsequent retreat, and left distinctive depositional features similar to those associated with cold-based glaciers in the Dry Valleys of Antarctica. These new observations provide additional support for a cold-based glacial interpretation of the Tharsis Montes fan-shaped deposits. Morphological evidence suggests that the largest of these graben was the primary source region for the most proximal smooth facies lobes at Arsia Mons, and map-plane ice sheet reconstructions are consistent with these observations. This relationship has significant implications for the relative ages of the individual facies within the fan-shaped deposit, including the possibility that the smooth facies represents several distinct phases of glaciation. The high relief and large elevation differences between the upslope and downslope walls of these graben appear to be critical factors for ice accumulation and the generation/collection of rockfall within glacial accumulation zones. We suggest that rockfall was the dominant process responsible for debris-cover formation on the glaciers sourced within these graben and consider the implications for the entire Arsia fan-shaped deposit. New crater count data suggest that the fill material in the large Arsia graben formed within the past $100 Myr (model age of $65 Ma). Taken together, these new observations provide additional evidence for several periods of Late Amazonian climate change on Mars within the past few 100 Myr resulting in episodes of tropical mountain glaciation. Finally, MOLA topography reveals that several lobate features interpreted as remnant debris-covered ice from the most recent phase of glaciation are presently hundreds of meters thick, suggesting the possibility of long-term, near-surface water ice survival in the equatorial regions of Mars.

Arecibo radar imagery of Mars: The major volcanic provinces

“…12b), is the largest of the three FSDs associated with the Tharsis Montes. Shean et al (2007) map the Arsia FSD extending northwest as far as 229.5°E. Our imagery shows this region (11-B, 9c-B) to be radardark, which is similar to the other two FSDs and consistent with a rock-poor, radar-absorbing mantle.…”

“…Like Ascraeus and Pavonis Montes, Arsia Mons has an associated northwest-trending fan-shaped deposit (FSD) that a recent study has interpreted as glacial in origin (Shean et al, 2007). This unit, which stands out in the MOLA roughness map (Fig.…”

Equatorial locations of water on Mars: Improved resolution maps based on Mars Odyssey Neutron Spectrometer data

“…Evidence, in the form of surface morphology and cratering, for late Amazonian tropical mountain glaciers on the northwestern flanks of the Tharsis Montes and Olympus Mons has been detailed extensively using observations from the Mars Express, Mars Global Surveyor and Mars Odyssey orbiters (Head and Marchant, 2003;Shean et al, 2005Shean et al, , 2007. The production of such glaciers at equatorial Mars today is impossible given the current climatic conditions.…”

Science Priorities for Mars Sample Return

“…Changes in the amount of entrained non-ice dust with depth would help to constrain estimates of the modulation of large-scale dust events and their seasonal variability (Herkenhoff et al, 2007). The desired sample localities include both north and south residual ice deposits, both north and south PLD, and both mid-latitude and tropical glacial deposits (Head et al, 2006;Head and Marchant, 2003;Shean et al, 2005;Shean et al, 2007). Ideally several core samples would be extracted over lateral distances of ~1 km to validate stratigraphic models based on orbital imagery.…”