In early 2002, a 200-meter-thick, Rhode Island–sized floating mass of ice attached to the Antarctic Peninsula unexpectedly shattered and floated away in a matter of weeks. While researchers quickly linked the breakup to lakes of meltwater that had accumulated on the so-called Larsen B ice shelf’s upper surface and then wedged apart deep crevasses, they hadn’t come up with a convincing explanation for what triggered the collapse. Now, a new analysis in Geophysical Research Letters suggests that the sudden drainage of one or more of those lakes, and not merely their presence, set off the disintegration. The team’s analyses show that when a meltwater lake drains through the ice sheet into the underlying sea, the ice nearby, suddenly relieved of the water’s weight, springs upward. That changes the patterns of stress in the ice, which ripple across the ice shelf and can cause nearby lakes to drain, setting up a chain reaction by which the entire lake-ridden portion of the ice shelf can splinter. Just before the collapse and its aftermath (shown as icebergs were dispersing on 7 March 2002), satellite images showed more than 2700 meltwater lakes on Larsen B’s surface. All of those lakes mysteriously and simultaneously drained just before the breakup commenced—a possible warning sign for future ice shelf collapses, the team contends.