Crack in the very earth of Michigan

Six years ago a crack suddenly opened in Michigan's Upper Peninsula.  Consider it an early skirmish in Earth's war against the human race:

Early in the morning, folks just north of Menominee, Michigan, heard a loud noise and felt a shake... [W]hen someone went out to finish cutting up a large tree that had come down in a storm two weeks previous, they found a huge crack had opened up in the Earth. It wasn’t going to swallow anybody whole, but you could probably have lost a cell phone in there.

Nonlethal so far, but the Menominee Crack is impressive:

The “Menominee Crack” was a little longer than a football field, over half a meter wide in places, and approached 1.7m deep. It ran through a forested area that had previously been flat. The crack actually sat atop what was now a six-foot-high ridge, with trees on either side now tipping slightly away from vertical.

And nobody can agree on a cause.  Best of all, there's a resonantly mysterious detail:

satellite photos from 1998 show a rectangular shape in the ground along the side of the road and ending near the crack. The only problem is that no one who lives there remembers what it was. Maybe it was a trench road crews borrowed dirt from at one point, or maybe it was just a small pasture or garden plot.

Maybe.

(thanks to Steven Kaye)

Comments

[Jim Parker]

http://www.freep.com/story/news/local/michigan/2016/02/11/crack-ground-michigan-wisconsin-menominee/80264196/

[Bryan Alexander]

That's one theory.
I wonder if it really is unique.