Geological Pop-Up Feature Found Near Menominee, Michigan
February 29, 2016
Photographer: Wayne Pennington
Summary Authors: Allison Mills; Jim Foster
The photo above shows a curious crack splitting the gentle landscape north of Menominee on Michigan's Upper Peninsula (UP). It formed in 2010 and is approximately 360 ft (110 m) long, up to 2 ft (0.6 m) wide and 5 ft (1.5 m) deep in places. In fact, this crack is associated with what's believed to be the UP's first recorded earthquake, a minor temblor that registered less than 1.0 magnitude.
Researchers from Michigan Technological University, led by Dr. Wayne Pennington, are confident that the feature is a geological pop-up -- confirmed by running seismic refraction tests. According to Pennington, what struck him as most unusual is the 6 ft (1.8 m) high ridge where the crack resides. The ridge appeared at the same time the crack opened. A pop-up may occur when the greatest principal stress of subsurface rock is horizontal and the smallest stress is vertical. Horizontal stress conditions can be relieved by movements in faults or removal of a load, such as rock being quarried, glacial retreat or perhaps even the elimination of a large tree. See cartoon.