Plain Language Summary
The behavior of Antarctic glaciers will largely determine the pace and magnitude of future sea level rise. But the projections made by ice sheet models are uncertain, in part due to the uncertain response of Antarctica to the future loss of its floating ice shelves. It has been hypothesized that ice shelf breakup could trigger a self-sustaining mechanism of ice loss whereby ice cliffs collapse under their own weight. This idea is controversial because it has not been unambiguously observed in modern glacier systems. We show that after the loss of its ice shelf, Crane Glacier experienced a 2 year period of accelerating ice loss, consistent with a geometric instability like the one proposed. Models of ice cliff failure that assume glacier ice has pre-existing weaknesses are more consistent with the behavior we observe at Crane than models that assume pristine ice.