In August 2012, the Jakobshavn Glacier was flowing and breaking off into the sea at record speeds, three times faster than in previous years. As the glacier flowed faster, it became thinner and more unstable and in a twist, a pileup of thick ice replenished the glacier's terminus, slowing it down again. New work explaining the fast-then-slow movement of Jakobshavn may help scientists better predict how tidewater glaciers contribute to sea level rise.