Models of the Antarctic Sheet are tuned using observations of historic ice-sheet behavior, but we have few observations that tell us how inland ice behaved over the last few millennia. A 2 km tall volcano sitting under the ice sheet has left a record in the ice as it flows by, and that feature provides unique insight into the regional ice-flow history. It indicates that observed, rapid changes in West Antarctica flow dynamics have not affected the continental interior over the last 5700 years.