Rock Elm Disturbance

Rock Elm Disturbance in western Wisconsin is a distinct impact crater about 6 kilometers across, formed when a meteorite about 170 meters wide struck at roughly 30 kilometers per second during the Middle Ordovician, about 455 to 430 million years ago. Its geology preserves evidence of the collision, including a raised central area where deeper material was forced upward and faulted sandstone exposed along the southern edge. The site may belong to a broader Ordovician meteor event linked to other Midwestern craters. It is also significant for yielding reidite, a high-pressure zircon mineral whose Rock Elm example is the oldest known occurrence.

Plum City, Wisconsin · United States