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(photos: JPL/NASA/MSSC)

Terrestrial analogs of Martian
radar targets from the Dry Valleys, Antarctica

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Terrestrial Analogs

Conditions on Mars are cold and arid, with polar ice caps that are composed principally of carbon dioxide and water. Water cannot exist in liquid form at the surface and at the near-surface ice would be rapidly sublimated at low latitudes, yet the amount and distribution of water in any form is of supreme interest in the search for life on Mars (Science Planning for Exploring Mars, 2001).

The Dry Valleys of East Antarctica have long been considered one of the best terrestrial analogs to conditions on Mars (e.g. Gibson and Ransom, 1981; Malin, 1985). They exist in a polar environment where the temperature rarely exceeds 0° C, and average about -23° C in their lower reaches (Thompson, 1971). The cold, dry conditions produce weathering products similar to those observed on Mars, and waters contained within the closed basins are mostly saline. Ice exists in a wide variety of deposits both above and below the surface. The large range of different features relevant to specific Martian subenvironments, all located within a relatively small region, makes it an ideal location for this type of study.

Features of primary interest to this effort on Mars include:

(click on thumbnails for a larger version of photo) all black and white Mars photos from Mars Orbiter Camera on the Mars Global Surveyor:

Viscous flow features:

Debris-covered glaciers:

Lobate features on steep slopes exhibiting pressure ridges and lineations (typically ~1 km width, ~5-6 km length) were identified in 72 MOC images by Milliken et al. (2002), who estimated shear stresses for a range of composition, thickness, ice volume fraction, and grain size. Corresponding strain rates based on creep deformation yielded a maximum age of ~3000 years (Milliken et al., 2002). In Dao Vallis, these formations appear to merge with a larger flow feature in the center of the valley, very similar to the behavior of terrestrial alpine glaciers (Arfstrom, 2002a).

Rock glaciers and debris flows

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Flow features identified in Viking imagery (Lucchuta, 1984) and previously identified as long-runout landslides (Shaller, 1991) are under investigation by Neel and Marston (2002) as possible rock glaciers (unsorted rock and ice mixtures that move primarily by creep deformation). Neel and Marston (2002) also identify a lobate feature (`300m width, `1000m length) in the Hellas Impact Basin as a candidate rock glacier.

Polar layered terrain:

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On the margin of the southern polar layered terrain, lobate flow features partially fill impact craters (Head, 2001; Pratt and Head, 2002) that have been interpreted to be Amazonian in age (Herkenhoff and Plaut, 2000), indicating that the polar layered terrain has moved vicously in recent geologic time. Since the polar layered terrains have been thought to contain a record of Martian climate variation (REF), evidence for flow deformationhas important implications for interpreting layer morphology.

Stagnant ice:

Alcoves:

Identified in MOC imagery and interpreted as possible liquid water erosion (Malin and Edgett, 2000), gullies within alcoves in Dao Vallis could have also be formed by long-term seepage of groundwater that subsequently freezes, gradually forming an ice sheet (a “filled” alcove) that is covered by dust and rock debris (Arfstrom, 2002b). When seepage slows or ceases, the ice is then completely sublimated, leaving behind a void due to the erosive effect of ice freeze/thaw. If this model is correct, then ice sheets currently exist in filled alcoves.

Permafrost and active layer:

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On Mars, the new GRS results indicate that near-surface permafrost may be more widespread than previously thought at mid-high latitudes. Small-scale (<10 meters), contraction-cracked, polygonal terrain with a few impact craters is evidence for recent (<10 Ma) melting of an active layer over an ice-rich permafrost (Seibert and Kargel, 2001).

Mars analogs (features found in the Dry Valleys):

Viscous flow features:

Valley glaciers:

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Valley glaciers terminate in all of the Dry Valleys. Taylor and Wright Upper Glaciers (~ 5-10 km wide, ~20 and 60 km long, respectively) are fed by the polar plateau, while others, generally much smaller, originate in hanging valleys along the sides (e.g., Rhone and Commonwealth Glaciers). Close to the coast, some glaciers emanate from Wilson Piedmont Glacier (e.g., Victoria Lower Glacier, ~ 7 km wide and ~ 20 km long). The toes of these glaciers are zones of deposition, ablation, and melting. Taylor is the most voluminous; it is cold based (Higgins et al., 2000) and is very slow moving (~ 15 to 5 m/a at the terminus; Robinson, 1984).

Rock Glaciers:

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Multiple rock glaciers emanate from side valleys and coalesce in upper Beacon Valley. Recent interferometric SAR results (Rignot et al., submitted), show that motion of the rock glaciers reaches a maximum of ~ 40 mm/yr and drops to near zero in the lower part of the valley.

Debris Flows:

Kilometer-scale mass-movement features have been identified on the slopes of Taylor Valley (Higgins et al., 2000). It is thought that these were subaqueous flows resulting from the advancement of an ice-dammed lake over pre-existing glacial drift.

Stagnant ice:

Buried ice:

Massive ice in lower Beacon Valley lies beneath ~ 50 cm of rock debris and till, and is thought to be the remnant of a late Miocene glacier (Sugden et al., 1995; Schaefer et al., 2000); hence, the oldest ice on Earth.

Ice-cored thrust moraines:

Evidence of prior advances of Taylor Glacier, these are preserved in dessicated form in Taylor Valley (Higgins et al., 2000) and currently exist at the terminus of Taylor Glacier.

Ice-covered saline lakes:

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A number of lakes and ponds of varying salinity exist in the Dry Valleys, generally ~ 1-2 x 3-5 km in areal extent and of ~ 15 – 70 m depth. Most appear to have initially formed from fresh glacial meltwater and became saline either by the accumulation of surficial salt deposits and/or atmospheric salts (Torii and Yamagata, 1981) or by connection to a deep groundwater system (Harris and Cartwright, 1981).

Permafrost and active layer

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Permafrost is found throughout the Dry Valleys where it is thought to extend over depths ranging from 250 to ~1000m (Decker and Bucher, 1980). This permafrost is overlain by an "active layer", up to a meter in thickness, where the temperature rises above 0° C (and up to 10° C) for some period during the year (possibly only a few days or hours; Cartwright and Harris, 1981). Polygonal patterned ground of scales from a few meters to tens of meters is common on the floor of the Beacon Valley and indicates the presence of liquid water in the shallow active layer (e.g. Berg and Black, 1966) and/or thermal contraction of permafrost (Lachenbruch, 1962; French, 1976).

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Last modified: 27 Aug 2004 13:29
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