DETECTING ICE WEDGE GEOMETRY USING GROUND PENETRATING RADAR

Polygonal terrain is one of the most common landforms in continuous permafrost environments. This terrain has diverse appearances and occurs in a variety of surface materials. It has been estimated that over 30 percent of the top meter of ground can contain wedge ice in these environments, and characterization of ice wedge shapes can lead to better estimates of ice volume. As part of several studies using geophysical methods to detect ground ice in the Canadian Arctic, GPR data were collected over polygonal terrain at two locations on Devon Island.

Polygon surface troughs varied in width from a thin depression to more than a meter. Although subsurface ice was not found beneath every trough, polygons with notable troughs contained fairly large ice wedges. At the Thomas Lee Inlet site east of the Haughton impact crater, polygons were formed in fine sediments, whereas they formed in gravel-to-cobble-sized deposits at the Lake Orbiter site north of the crater.

GPR data were collected at 200 and 400 MHz and show the thickness of the active layer, the widths of the ice wedges, and other subsurface stratigraphic features very well. Locations and widths of wedge ice were confirmed by augering and trenching to the tops of a sample of the ice wedges.

Ice wedge edges are clearly delineated in the GPR data, which enables a fairly accurate estimate of their widths. Additionally, surface tensional cracks above wedges at the Thomas Lee Inlet site correlate with the edges detected in GPR data. The tensional cracks are likely due to subsidence that may result from downward melting of the ice wedge in response to increasing temperatures over several years or more. This surface indicator of active layer thickening may be useful for studying past and current climate change in Arctic regions. Additionally, many polygonal features have been observed on Mars, so more detailed studies of terrestrial features may help to understand which could contain large amounts of subsurface ice.