The realization that in-situ and near in-situ ashfall up to 15 million years in age rest directly on the modern Dry Valleys landscape has prompted us to take a closer look at the range of periglacial processes operating in region. As part of this effort, we have deployed meteorological sensors (Onsett HOBO® data loggers) throughout the valleys in order to determine the spatial distribution and magnitude of microclimate variation, and to assess the resultant surface processes/ landforms that are endemic to each microclimate zone.
On the basis of measured variations in summertime atmospheric temperature and relative humidity (RH), soil temperature, average wind speed/direction, and soil moisture, we divide the region into three microclimate zones: a coastal thaw zone (CTZ), in which elevated soil temperatures and seasonally-moist soils foster development of saturated active layers; an inland-mixed zone (IMZ), in which abundant surface water and saturated active layers are restricted to the margins of melting snowbanks, ephemeral streams, and thawed-lake margins; and, a stable-upland zone (SUZ), in which atmospheric and soil temperatures are too cold and dry to permit the development of traditional, saturated active layers.
Equilibrium landforms are those that are endemic to, and in balance with, local microclimate conditions in each zone. Our assemblage of equilibrium landforms in the CTZ includes tafoni, solifluction lobes, thermokarst, ice-wedge polygons, and low-gradient slopes with mature, low-density gullies. In the IMZ, equilibrium landforms include gelifluction lobes, sand-wedge and composite polygons, desert pavements with wind-polished cobbles, and immature, closely spaced gullies. Finally, equilibrium landforms that best characterize the SUZ include sublimation polygons, debris-covered glaciers, pitted surface cobbles, salt-cemented duricrusts, and puzzle rocks.
Of particular interest are the unusual landforms and surface processes endemic to the SUZ, in which environmental conditions are among the most Mars-like on earth (click here for more details on our Mars-Antarctic analog studies). Within the SUZ, we have studied, and modeled, the formation of sublimation polygons, the magnitude of warming that would initiate slope failures (e.g., shallow planar slides that today occur in the CTZ), and the rate of vapor-diffusion from buried-ice surfaces to the atmosphere. For the latter, we have shown that buried-ice deposits in the SUZ sublimate at an average rate of 0.1 mm a-1, with rates reduced to <0.001 mm a-1 if summertime temperatures drop by ~3°.
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