Bed properties and hydrological conditions underneath McCall Glacier, Alaska, USA.

During three summer field seasons (2003, 2005 and 2006) we carried out radio-echo sounding
measurements with a 5MHz (central frequency) ice-penetrating radar on McCall Glacier, Arctic
Alaska, USA, along the central flowline and 17 cross-profiles. Two-way travel time was, after migration,
converted to ice thickness, which, in combination with a recent digital elevation model of the surface
of the glaciated area, resulted in a detailed map of the bed topography. This reveals a complex basal
topography in the confluence area of the different glacial cirques. The pattern of subglacial water
flow following the hydraulic potential gradient was calculated for the whole glacier area and shows a
confluence of subglacial water downstream from the confluence of the glacier cirques. From the ice-thickness map the total ice volume was estimated as slightly less than 0.5 km3. Bed reflection power
(BRP) was determined for the glacier after correction for ice-thickness dependence. Results reveal a
clear relationship between the BRP pattern and basal sliding anomalies along the central flowline.