a lake can vanish in hours

and when one does, it's telling you something about the ground underneath.

Most of Alaska sits on permafrost. Soil that stays below freezing for years at a stretch, packed full of ice. When that ice melts the ground just drops, and whatever got built on top of it drops too. Houses, roads, pipes.

Here's what makes it trackable. When the ground sinks, water fills the dent and you get a pond. There are roughly 70 million of those little ponds scattered across the Alaska tundra.

Sometimes the same thaw that made a lake also cuts it a drain. A lake that took a thousand years to form can empty out in a few hours.

So a team of scientists pointed artificial intelligence at satellite images and started watching for exactly that. They're monitoring more than four million lakes across the Arctic now, close to real time.

In June and July of this year alone they caught about 30 more lakes draining up in the northwest part of the state. That's after a winter that actually ran cold for Alaska.

And the reason any of this matters to a normal person is the map it produces. It shows which ground is loaded with ice and a bad bet to build on, and which ground will actually hold a house.