2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 10
Presentation Time: 10:30 AM


FORTIER, Gisele F.1, SMITH, Ryan C.1, SJOGREN, Darren B.1 and NEUDORF, Christina2, (1)Department of Geography, Univ of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, (2)Department of Geography, Univ of Saskatchewan, 9 Campus Drive, Saskatoon, SK S7N 5A5, Canada, gffortie@ucalgary.ca

Large-scale glaciotectonic deformation is the faulting and folding of sediments and bedrock dominantly due to the compressional and extensional forces imposed by an advancing ice mass. The resulting features can be readily observed in many exposures along the shores of the McGregor and Travers Reservoirs in southern Alberta, Canada. This, however, is simply a two-dimensional representation of three-dimensional features. To fully understand the style of deformation, it would be beneficial to obtain an image of the structures behind the visible face. A variety of shallow geophysical methods are available to that end. Electrical Resistivity Imaging (ERI) is a method that measures the degree to which a material resists the flow of electrical current. If a current is introduced into the ground, the resulting electrical field can be measured. This way, a two-dimensional cross section can be produced showing the resistive properties of a sediment package several meters behind an exposure. This aids in the interpretation of the material and structural features that may be present but not exposed.

Electrical resistivity is a function of porosity, saturation, material texture, and resistivity of the pore fluids and the solid phase. Resistivity data was collected using the Sting-Swift R1 IP resistivity meter. A 38 meter line, with one meter electrode spacing, was run four meters back from the exposure. Two separate types of arrays were used to take measurements: (1) the Wenner array and (2) the dipole-dipole array. By combining the results of these two arrays, a more accurate depiction of the subsurface is possible.

This methodology was successful in imaging subsurface architecture. Tills, fluvial and lacustrine sediments, bedrock, and structural features such as faults, exhibit large contrasts in their physical properties. Electrical resistivity imaging, when integrated with detailed geomorphologic analysis, provides enhanced insight for inferring the processes of sediment emplacement and deformational processes. Preliminary results indicate that the sediments that make up the hummocky landforms were not emplaced by supraglacial meltout as with traditional models, but underwent subglacial or proglacial emplacement and deformation.