The dynamic behavior of the West Antarctic ice sheet is of interest because of the possibility that it may change and cause rapid sea-level rise. Attention is focused on the fast-moving and rapidly responding ice streams that drain the ice sheet. One of these, ice stream C, largely stopped about a century ago, and some models for this shutdown postulate negative feedbacks that would tend to stabilize the ice-sheet. Here, new data are presented indicating that the slowdown of the ice stream is restricted to its lower part, and occurred because of loss of lubrication on localized sticky spots at the bed of the ice stream. The increased friction probably arises from a topographic accident of the glacier bed that has directed lubricating water to the neighboring ice stream B, together with slow drawdown of the ice sheet, rather than from any general stabilizing feedbacks.¿ 1997 American Geophysical Union