Editor's Note: Vienna, Austria-based science writer Chelsea Wald is taking part in a two-week Marine Biological Laboratory journalism fellowship at Toolik Field Station, an environmental research post inside the Arctic circle. To see the current conditions in Toolik, check out the Webcam.

I was nearly eaten by a thermokarst. I just stepped in and, before I knew it, I was sucked in up to the top of my big rubber boot.

I'm not that familiar with thermokarsts, so I didn't know quite how to act around one. Basically, thermokarsts are what sometimes show up when permafrost thaws. Permafrost is frozen soil—technically, it has to be frozen for two years in a row to be called permafrost. If the soil thaws, its surface sometimes collapses. Thermokarst is thawed, collapsed permafrost.

But knowing the definition didn't prepare me for the reality. I had taken a helicopter out to one of the important thermokarst sites on Alaska's North Slope, where hydrologist Mike Gooseff of Penn State is working. This one formed following a massive fire that burned 1,000 square kilometers of the Arctic tundra in 2007. It's on the banks of a lake and sort of looks like a mudslide in slow motion, slumping gradually into the blue waters. Some of the vegetation on the thermokarst seems to be hanging on, but other sections are just gloopy mud slops.

It's into one of those gloopy places that I stepped—and sank. First, my boots went up to the ankles. I wasn't too worried. But the more I struggled, the more I sank. I finally got one boot out, but at the cost of the other. When I was in up to the top of that boot, Mike got a shovel and started to excavate, to little effect. Eventually, I decided to cut my losses and pulled my foot out of my boot. That proved to be the right decision. With me out of the way, Mike and one of my traveling companions were able to dig the boot out and rinse it in the lake. But not before getting pretty muddy themselves.

I don't think a thermokarst has ever actually sucked down a person, but thawed permafrost can cause problems under buildings and roads, or by the sides of waterways. Scientists are quick to tell you that thermokarsts are natural features—you can see scars all over the landscape that may be old thermokarsts—but comparisons of photos from aerial surveys in the 1980s and 2000s show that the number of active thermokarsts seems to be growing.

It's not unreasonable to think that the rise in thermokarsts is the result of global warming. Temperatures are rising faster in the Arctic than anywhere else on Earth, and warmer temperatures naturally lead to thawing. Warmer temperatures also lead to more fires, which seem to cause at least local permafrost failures.

The most frightening thing about thermokarsts—aside from the fact that they eat people—is that they could contribute to a global warming feedback loop. Lots of carbon is trapped in permafrost, and when the permafrost thaws, that carbon becomes available to microbes, which turn it into carbon dioxide and release it into the atmosphere, leading to further warming. Once that's happened enough, it could become a runaway feedback loop that's impossible to stop. No one knows if we've passed that tipping point already.

At least I'm still here to write about it.

Image: Scientist Mike Gooseff shoveling Chelsea Wald out of a thermokarst; photo courtesy of Christopher Neill