Photo by Kevin Wolf.

D.C. is not actually built on a swamp, they said. Well, explain this, pedants: D.C. is literally sinking into the ground, according to geologist Ben DeJong. Science!

The city could drop by six or more inches by 2100, which doesn’t sound like a lot, but will add to the already predicted problems of sea-level rise and tidal flooding.

Scientists have known for 60 years that sea level in the Chesapeake is rising at twice the global average rate, which has led to the hypothesis that it isn’t just the water rising but the land sinking. Ben DeJong of the University of Vermont and his team have confirmed this by drilling a bunch of holes in Maryland. (Science!)

Here’s how it’s happening: During the last ice age, a sheet of ice stretching to Long Island put so much weight on the earth that the mantle, underneath the earth’s crust (think back to your fifth-grade geology class, kids) squished away from the ice, i.e. south. So the land south of Long Island got pushed up. As the ice began melting 20,000 years ago, the land started to sink again.

It’s as if the city is “sitting on one side of a water bed filled with very thick honey,” DeJong said. The ice sheet was a person sitting on one edge, and D.C. is the cat sleeping on the other side. When the person stands up, the cat starts to sink. (All science metaphors should have cats in them.)

Anyone interested in the actual methodology of the study can read more here or see the full study here.

D.C. is already predicted to be at risk of tidal flooding—in 30 years, the city will average 240 floods per year, and according to the Union of Concerned Scientists they’ll be more than just minor annoyances. Good thing we’re super prepared for those!