Melt pond falls through ice in Greenland

Watching flow sharpens picture of moving glaciers

It took almost a month for meltwater to accumulate atop Greenland’s ice sheet in the summer of 2006. It took only 90 minutes for all that water — a lake so large it could fill New Orleans’ Superdome more than 12 times over — to pour through a crack in the kilometer-thick ice below it and drain the lake dry.