CGRG Bibliography of Canadian Geomorphology
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Author : Bode, J.A.; Moorman, B.J.; and Solomon, S.M.
Date : 2008.
Title : Utilizing ground penetrating radar to calculate ice wedge volumes.
Publication : Joint Annual Meeting of the Canadian Geophysical Union and the Canadian Geomorphology Research Group. May 11-14, Banff, Alberta.
Issue :
Page(s) :
Abstract
One of the more striking features of polar regions is the presence of ice wedge polygons. Ice wedges are significant because once the ice melts the ground loses its strength to support overlying material which can lead to subsidence. This is of particular concern because as development increases in the North, infrastructure and other anthropogenic activity can alter the subsurface thermal regime leading to a melting of ice wedges. Quantifying the volume of an ice wedge is hampered by the fact that the ice is beneath the ground surface which makes them difficult to observe and measure. Pollard and French, 1980 estimate the volume of ice wedges assuming a triangular prism morphology (V= ½ L*W*D). They used aerial photos to determine the length and width. However the did not have any control of the depth as they used an assumed ratio of 3:1, the depth of the ice wedge being three times the width. They also did not account for the active layer thickness. Working on Taglu Island in the outer Mackenzie Delta we use aerial photos to measure the length and width of ice wedges. Aerial photos taken in August 2004 were used to measure the length and widths of ice wedges in the study area. The ice wedges were digitized in ArcGIS and to get the total length of ice wedges and representative width measurements were made to get the average width. Rather than using an assumed ratio for depth we used ground penetrating radar (GPR) data to determine depth. Data were collected in the winters of 2007 and 2008 around the southern portion of Taglu Island. Reflections from the base of the ice wedge due to dielectric differences in frozen sediment and ice allow calculation of ice wedge depth to be made. Using GPR we also obtained the average depth of the active layer. With this information we adjust the equation used by Pollard and French, 1980, to V= ½ L*W*(D-DAL) were DAL is the average depth of the active layer. Additionally, we use GPR data to verify the width measurements made form aerial photos. Results showed that by combining remotely sensed imagery and GPR data, the volume of ice wedges could be better estimated. Initial results from the GPR data show that the depth to width ratio in this area is considerably less than 3:1. Ground penetrating radar also offers information on the position of the edges of the ice wedge unlike aerial photos which only offer information on the ramparts. As climate warms, sea levels rise, and development intensifies in the North, quantifying excess will become increasingly important as the melting of excess ground ice has the potential to significantly alter the northern landscape.
Bibliography of Canadian Geomorphology