Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p22a..04l&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P22A-04
Mathematics
Logic
0702 Permafrost (0475), 0706 Active Layer, 0772 Distribution, 6225 Mars, 9310 Antarctica (4207)
Scientific paper
The generation of thermal contraction crack polygons on Earth and Mars is a complex process, governed by the interplay between climate or microclimate conditions and the physical properties of the cracking medium. The morphological evolution of thermal contraction crack polygons is controlled in large part by local climatic and geological conditions: principally, the presence or absence of a seasonally wet active layer; the abundance of windblown, crack-filling material (snow or sediment); and the temperature and humidity conditions controlling the transport of water vapor between the ice-rich substrate and the atmosphere. Thermal contraction cracking of ice- rich soils is expected under present Mars conditions for latitudes polewards of 30 degrees, and a correlation between polygon size and latitude is predicted: larger stresses generated polewards will produce finer polygon networks. Observations confirm this general prediction, and a latitude dependence of polygon morphological type is observed, suggesting that the latitudinal range of current climate conditions is partially responsible for the difference in morphology. In particular, some hypothesize that localized melting and freeze-thaw processing are a significant source of the variety in polygon morphologies observed. A suite of thermal contraction crack polygon morphologies has been documented in the Upland Stable Zone (USZ) and Intermediate Mixed Zone (IMZ) of the Antarctic Dry Valleys, forming under known microclimate and subsurface rheological conditions, informing a comparison with polygonally patterned ground observed on Mars. We address the questions. What do current climate conditions suggest about the equilibrium conditions under which polygons are evolving on the martian surface? Is the decreasing spacing of thermal contract crack polygon networks polewards entirely a climate signal, or is there also a substrate rheology signal? What polygon features require freeze-thaw processing, and what features compare favorably to morphologies observed in the Upland Stable Zone? Does Mars have a latitude-dependent transitional Intermediate Mixed Zone? What do fossil sand/ice wedges look like on Earth as compared to Mars, and how do they change our understanding of the geomorphic effects of current Mars climate conditions?
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