After five years, researchers have finally found a possible explanation as to what caused the strange crack in Earth to occur in Michigan: a pop-up in the upper layers of limestone, a new study suggests.
On October 4, 2010, the elevated soil and rock were found in a forest near Birch Creek on Michigan’s Upper Peninsula, north of Menominee. Because of the powerful sound, which thundered through the forest, nearby homes were shaken with a strength that equates to a magnitude-1 earthquake.
Locals came across the crack – five feet (1.7 m) deep and 360 feet (110 m) long – the next day. At its largest point, the ridge was thirty feet (nine m) wide and seven feet (two metres) high. On each side, trees leaned away from the massive crack at approximately fourteen degrees.
Wayne Pennington, senior author of the study and dean of the College of Engineering at Michigan Technology University (MTU) in Houghton, said that even the trees’ roots had been torn due to the forces that created that crack.
For the study – published in the journal Seismological Research Letters – Pennington and students at Michigan Technology University conducted a seismic analysis. According to them, the most plausible explanation for the crack would be a pop-up in the layers of limestone, which are located right beneath the clay layers of soil. Still, the researchers are not one hundred percent sure what caused the pop-up.
To survey the underground rock, the team used a sledgehammer, slammed it into a metal ball that was placed on the ground, and then observed how the sound waves travelled through the rock and soil layers below. The researchers found a buckle in the limestone layers beneath the crack.
Based on the analysis, when the pop-up appeared, the limestone layers heaved upward. Along the ridge, the clay soil is approximately five feet (1.5 m) deep, according to the researchers. As it bent upward, the stretching of the surface caused the crack to appear.
Penn also said that the crack did not occur due to an earthquake, because the pop-up appeared in the uppermost bedrock. Earthquakes usually strike miles deep, he added. Ever since 2010, two moderate earthquakes have occurred in Michigan; however both were in areas unrelated to the mysterious crack.
In quarries in eastern North America, pop-ups are quite common; they can also take place after glaciers retreat.
Image Source: geo. mtu