AbstractDuring a 3‐year period, several aspects of the glacier‐rock interface were studied in a cavity beneath 5–8 m of ice near the terminus of Grinnell Glacier, Montana, U.S.A. Continuous week‐long records of the summer sliding rate revealed a very uniform speed of about 12 m a−1during the summer, a value about 20 per cent higher than the average annual sliding rate. Several decimetre‐sized rock fragments were broken from the glacier bed near the lee sides of bedrock ledges and transported down‐glacier. In the course of a two‐week long experiment, the glacier abraded its bed significantly and non‐uniformly. It is of interest that significant quarrying and abrasion occurred under thin ice with relatively little