Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.c22a..08g&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #C22A-08
Physics
0702 Permafrost (0475), 0704 Seasonally Frozen Ground, 0710 Periglacial Processes, 0774 Dynamics, 4460 Pattern Formation
Scientific paper
The polar regions of both the Earth and Mars host a surprising variety of surface patterns. These arise from complex interactions between soil, ice, and in some cases, liquid water, and can dominate the dynamics of near-surface soils in these regions. However, the rates at which these processes work are still poorly constrained. We present observations of polygonal terrain, which occurs in areas of icy permafrost that see large temperature variations over the year. The winter cooling creates a large stress in the ice component of these soils, causing fracture. While the cracks are open, snow and detritus can fall into them. Thus, in the summer, when the cracks relax, there is a net addition of material. Over many such cycles, the crack networks grow and develop into beautiful regular polygons. We have recently made measurements of the surface topography and trough dynamics of sand-wedge polygons in Beacon, Taylor, and Victoria valley, of Antarctica. In Beacon and Taylor Valleys we report new measurements of the inclination, rod height, and inter-rod distance of a series of rods which were originally introduced into the polygonal landscape in the 1960s, and which serve as a long-baseline study of soil motion. In all three valleys we have surveyed the surface topography of several polygons, by theodolite. We focussed on characterizing the size, and shape, of the mounds which surround the crack troughs, and measured the height profiles of the ice-cemented soil horizons around the troughs. Assuming steady-state conditions, these measurements allow an independent estimate of surface soil motion rates. Our observations will be used to refine models of polygonal terrain, and to tie into efforts to understand the history and evolution of surface, and near-surface, features in the Dry Valleys. With the Phoenix mission's recent observations of subsurface ice on Mars, it is also hoped that a deeper understanding of terrestrial features will also aid in our understanding of how polygonal terrain develops there.
Goehring Lucas
Hallet Bernard
Sletten Ronald S.
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