Three Dimensional Analysis of a Proglacial Clastic Dyke Network Using Ground Penetrating Radar, Skeidararsandur, Iceland

Researchers have studied the subglacial and proglacial impacts of glacial outburst floods through observation and measurements during flooding events and through analysis of the landscape and sediments after flooding events. While both erosion and sediment deposition dynamics have been studied extensively (eg. Sharp, 1985; Rijsdijk et al., 1999; Van Der Meer, 1999; Overgaard and Jakobsen, 2001; Glasser et al., 2003; Russell et al., 2006;); the routing and effects of pressurized groundwater during glacial outburst flooding are currently poorly understood.The objectives of this research are; 1) to test whether or not Ground Penetrating Radar (GPR) can can effectively image nearly vertical subsurface sedimentary structures thought to result from hydrofracturing of consolidated and confined glacial outwash sediments; 2) to determine if these subsurface sedimentary structures are in fact derived from pressurized groundwater.The site of this study is on western Skeidararsandur, Iceland, near the Sula river. Skeidararsandur is the largest glacial outwash plain on Earth encompassing an area of approximately 1300 km2 (Klimek, 1973). Because it is subject to frequent glacial outburst floods (Roberts et al., 2002) it makes an excellent laboratory to study glacial outwash structures. There are many surface ridges that have been interpreted as groundwater escape structures and correlated to previous outburst floods (Russell et al., 2006; Munro-Stasiuk et al., 2009). In addition, clastic dykes appear to represent groundwater escape pathways through the sands and gravels of the sandur (Munro-Stasiuk et al., 2009). GPR was able to detect steeply dipping clastic dykes and direction of flow at the study site. In addition, GPR can detect sinuous subsurface linear geologic features using proper scan orientation. The results of this study will lead to a better understanding of the dynamics of pressurized groundwater escape mechanisms resulting from sudden glacial outburst flooding. They will also help determine how pressurized groundwater moves through, interacts with, and responds to the sedimentary environment. Understanding how pressurized groundwater behaves will allow us to design better abutments, foundations, cores, and liners capable of withstanding immense stress. GPR gives us a non-destructive and inexpensive method that can be used to a depth of several meters for surface scans and as deep as needed in bore hole scans.