“We started hearing a noise, like breaking, or coins falling,” says Marco Tedesco, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. He makes a loud, sustained crunching sound, recreating what he and his team heard, years earlier while doing fieldwork on the Greenland Ice Sheet. Below the surface of the ice near where they were standing, a flood had begun. “The water below starts to move, but you still have snow on top,” Tedesco says of the phenomenon. As the flowing water gains momentum, overlying snow and ice give way and reveal a meltwater stream or river.