Rock Elm Disturbance, Impact structure in Pierce County, Wisconsin, United States
The Rock Elm Disturbance is an impact structure in Pierce County, Wisconsin, formed by a meteorite collision that altered the local bedrock. The site displays a raised central area surrounded by faulted sandstone layers that reveal the violence of the ancient impact.
This impact structure formed during the Middle Ordovician Period, roughly 440 million years ago, when a meteorite struck the Earth with tremendous force. The collision fundamentally altered the rock layers across this region of Wisconsin.
A graduate student from the University of Wisconsin-Madison first identified the distinct geological characteristics of this area in 1942, initiating scientific investigations.
The best way to view this site is from Nugget Lake County Park, where exposed rock layers from the impact zone are visible. The park provides easy access and allows you to walk through the disturbed area without special equipment or preparation.
Scientists discovered reidite at this location, a rare and dense form of zircon that only forms under extreme heat and pressure from impact events. These samples rank among the oldest known examples of this mineral anywhere on Earth.
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