INTERNAL STRUCTURE OF A ROCK GLACIER ON MOUNT MESTAS, CO, USING GROUND PENETRATING RADAR (GPR): A PRELIMINARY ASSESSMENT

The internal movement of rock glaciers has been a source of speculation by researchers for almost a hundred years. Various speculations have resulted in lively debates, but none grounded in evidence. The numerous models that have been proposed suggest movement as semi-solid body deformation, thin layer deformation, internal sliding along movement planes, basal sliding, or combinations of all these variouls mechanisms. But, real data from the interior of a rock glacier are scarce.

Ground Penetrating Radar (GPR) “looked” at the internal structure of various landforms, including rock glaciers. These looks into the interior have aided researchers in their quests to model and explain the internal deformation and movement. Nevertheless, one has to question how well does the GPR profile mirror the true internal structure of the rock glacier? Unfortumately, no one has compared a GPR profile with the actual internal structure.

We used a rock glacier on Mount Mestas, that was excevated by the Colorado Highway Department in the 1960s as they searched for a borrow source for the constructuion of a new highway through La Veta Pass, as an opportunity to compare data from the GPR profile data with the interior structure. The ~4.5m wide, ~61 m long, and ~23 m deep excevation provides a window to compare GPR profile data with the actual internal structure. GPR data were collected using a PulseEKKOTM 100A system from Sensors & Software, Inc. at frequencies of 25 MHz and 50 MHz. Readings taken with the antennae parallel and perpendicular to the transect, at a step size of 1 m for the 25 MHz and 0.5 m for the 50 MHz antennae, allow analysis in 3-D. Preliminary analyses of these data suggest the internal structure as seen in the exposed trench. Enhanced processing and enhacement of data from the GPR profile should facilitate a closer match with the more subtle parts of the data profile.