The University of Colorado and Caltech, together with personnel from the U.S. Geological Survey and the University of Washington, drilled through Columbia Glacier at two locations (ice thickness 975 and 560 m) 9 km apart in the summer of 1987. Fluctuations in basal water pressure, water input as rain or ice melt, and surface-ice velocities were measured at short time intervals continuously during July and August. Surface velocities are essentially equal to sliding velocities in these areas of rapid flow (3–10 m/d) and high basal water pressure (nearly equal to flotation).

Experiments at the bed (planned and unplanned) suggest a thin layer of deforming fluidized material at the base, overlying rough bedrock. The sliding rate showed daily peaks related to peaks in ice melt, and longer-period peaks due to rainstorms or windstorms. Basal water pressure showed daily peaks related to water input, but did not necessarily rise at the times of storms and, in some cases, showed step-like drops at the end of these storms. No evidence was seen of “mini-surge” events or traveling waves of either sliding or water pressure. The Columbia Glacier results suggest that sliding is not a function of just driving stress and effective pressure; the amount (thickness and/or areal extent) of water, or possibly the rate of change of water input, will have to be considered.