A mystery from Menominee, Michigan may be closer to being solved.
A large crack opened in the ground more than five years ago. It was originally thought to be the result of an earthquake. But now there's another theory.
Eileen Heider remembers the jolt like it was yesterday.
"I was sitting watching television on my recliner, and I start moving. It was weird. Maybe only lasted 15 seconds, but it was moving," Heider said.
Heider says a large crack in the ground opened on her Menominee Township property in October of 2010. She thought it was an earthquake.
"Yeah, that's what I kind of thought," said Heider.
Over the last five years, scientists and students from Michigan Tech examined the area.
"When I got there I was completely shocked by what I saw," said Wayne Pennington, Michigan Tech Dean of Engineering.
Pennington says it was no typical earthquake.
"The crack is remarkable, but the ridge, a six-foot-high ridge, the length of a football field. That doesn't happen easily inside the earth," he said.
Pennington says underground pressure on the limestone rock in the area was released, allowing the crack to form. The scientific term is a geological pop-up.
"Usually it's caused by the removal of a glacier. But the glacier left here 11,000 years ago. So why did it wait until 2010 to happen?" asked Pennington.
Pennington says there are other less likely theories as to what caused the pop-up. He says the event is unique, and very rare.
"All the stress in that area has been relieved. If it was waiting 11,000 years for the final trigger, there's not a lot more stress there waiting to happen," said Pennington.
Meanwhile, Eileen Heider says she's happy to share her backyard with some geologic history.
"It's kind of a neat thing in some ways. As long as nobody got hurt, that's what counts," she said.
Heider says it was lucky the crack popped up where it did, and not near her home at the top of the hill.
As far as the earthquake, scientists say it did register on a seismograph.