An Innovative Technique for Using Ground Penetrating Radar to Track Ice-Flow Velocities at Depth, Matanuska Glacier, Alaska

Ground penetrating radar (GPR) data will be presented to demonstrate an innovative technique for determining glacier flow velocities at depth. A metallic target fixed in a borehole within a glacier can be detected using GPR when either the borehole is water-filled or the borehole is allowed to close around the target. In addition, the vertical and horizontal position of the target within the ice can be determined by collecting a grid of GPR data surrounding the borehole. Furthermore, by re-collecting the grid of GPR data at known time intervals, the velocity of the target--and hence the glacier flow velocity at the point of the target--can be estimated. An example of this technique will be presented. The study area is the western terminus of the Matanuska Glacier, a 35-km-long temperate alpine glacier located in the Chugach Mountains of southeastern Alaska. In July 2002, several targets were positioned at various depths in two boreholes (80-120-m deep) drilled near the terminus. The GPR data were collected several times during a month-long period in July and August 2002, and again during a week-long period in October 2002.