Flying over the Greenland Ice Sheet several days ago, scientist Mark Behn was surprised to see South Lake still full of sapphire-blue water. The 2- to 3-kilometer-wide lake forms each spring and summer, fed by melting ice. The water eventually builds up so much weight that it cracks the ice at the bottom of the lake, and the water drains away through the ice. That should have already happened by now.

Mark was thrilled to see the still-brimming lake. Rarely have scientists had an opportunity to witness a draining lake, which is why they put many instruments around the lakes to capture the action while they are not there. Mark and his colleagues had just gotten word that another lake they were scheduled to visit, North Lake, had just drained. “We just missed it,” he said. “We were all bummed.”

But maybe they would get to see it actually happen at South Lake before they had to leave for North Lake.

Waiting for a lake to drain is a little like waiting for a baby to be born. People know from previous experience approximately when it is going to happen—in the case of the ice-sheet lakes draining, sometime in mid-summer. But there really isn’t a set date or time. People have figured out that volcanoes may rumble or smoke days before they erupt, but scientists don’t yet fully understand the signs that signal that an ice-sheet lake is ready to go.

We learned today that a draining lake can get started slowly. But then it happened, sending crackles, pops, and gunshot booms through the air. And we started running.

Read on about our adventure at polardiscovery.whoi.edu.