54 Ground-Penetrating Radar Investigations for Geologic Formations

Tuesday, 19 March 2013
3:55 PM - 5:40 PM
Jefferson Room

USING GROUND PENETRATING RADAR TO DETECT MASSIVE GROUND ICE AND ICE WEDGE GEOMETRY IN THE CANADIAN ARCTIC

Paper number: 54-4
Program: Theme Sessions
Time: 4:40 PM – 4:55 PM

Authors

Abstract

Ground penetrating radar was used to detect massive ground ice in the western Canadian Arctic and ice wedges in the Canadian High Arctic. One goal of these studies was to use GPR and resistivity instruments to estimate volumes of ground ice, because these ice volumes are important for predicting landscape response to changing thermal conditions. The variety of locations allowed for data collection over ice bodies of different sizes and in different sediments, which leads to a larger population of examples from which to draw conclusions. In addition to ice bodies, GPR was also used to detect the base of the active layer and sedimentary structures within permafrost.

Massive ground ice was detected at several locations in the Mackenzie Delta using GPR, and was confirmed with resistivity data and, in one case, a sump pit. Fieldwork there was conducted in winter, so trenching and coring by hand was not feasible. These massive ice bodies ranged in size and depth, but were mostly formed in sand. At several locations, subsurface sedimentary structures were also detected. Although not targeted specifically, two transects passed over a some small ice wedges.

Ice wedges were the main target at locations on Axel Heiberg and Devon Islands in the Canadian High Arctic where subsurface material ranged from sands to cobbles. Fieldwork there was conducted during the summer when the active layer was thawing, so some of the sites contained a significant amount of water. Although the fresh water did not greatly affect the GPR data, it did complicate analysis of some resistivity data. GPR data of these ice wedges has been correlated with surface polygons, whose appearances depended on the sediment properties and wedge size. Although subsurface ice was not found beneath every trough, polygons with notable troughs contained fairly large ice wedges. These ice wedges are clearly detected in the GPR data, allowing fairly accurate width estimates for the tops of the wedges. Correlation of surface troughs with GPR-determined wedge widths shows that ice wedge volume estimates based on trough widths at the surface may be overestimated by up to 70%. Overall, GPR reveals subsurface information that will lead to a better understanding of subsurface ice volume and how that relates to surface features.