Source of the Mysterious Menominee Crack in Michigan May Finally Have been Solved

A mysterious crack in the ground has appeared in Michigan, and now seismologists think they may know what the feature is. Scientists believe that the crack may be a "pop-up" feature.

Pop-ups occur in places where shallowly-buried rock layers spring upward after having been weighed down by rock or ice. Pop-ups-sometimes called "A-tents" for their shape-may develop in places where the earth rebounds upward after an overlying glacier shrinks away, or when rock overburden is removed in a quarry.

With that said, the last glaciers retreated from Menominee about 11,000 years ago, and there isn't any quarrying in the area. This means that this particular pop-up, which stretched 110 meters, and was as deep as 1.7 meters in some places,  could be a one-of-a-kind event.

"I kept trying to think of ways that there could have been an uplift from a thrusting earthquake or something, but anything like that requires such a huge amount of displacement in order to produce that amount of crustal shortening, that nothing made sense," said Wayne Pennington, one of the researchers, in a news release.

The researchers used seismic refraction to confirm that the feature was a pop-up. When they confirmed it, the researchers then did a bit of detective work to find out why it appeared. It's possible that the limestone in the area may have been stress almost to the point of cracking when the last glaciers retreated. Then, the recent removal of a double-trunked pine, which may have weighed over two tons, could have been the final straw.

"There's a 60 percent chance that this explanation we provide is the right one," said Pennington. "But since we haven't seen this kind of thing elsewhere, and the tree is such a small effect, we wonder if there might be something else."

The findings are published in the journal Seismological Research Letters.

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