Decorah

Decorah Crater

The Decorah crater, also known as the Decorah impact structure, is a potential impact site located on the eastern edge of Decorah, Iowa, in the United States. This geological feature is theorized to have been formed by the impact of a meteor approximately 200 meters (660 ft) in width. The event is estimated to have occurred during the Middle Ordovician Period, roughly 470 million years ago.

Description and Significance

This impact structure is estimated to have a diameter of about 5.6 kilometers (3.5 miles). Significantly, the crater is entirely covered by the Winneshiek Shale, a geological formation that lies more than 50 feet below the current riverbed of the Upper Iowa River. Consequently, there is no visible evidence of the impact on the Earth's surface today. The force of the impact, estimated to be equivalent to 1,000 megatons of TNT, was substantial enough to depress the underlying Ordovician and Cambrian bedrock by several hundred feet, though it is not believed to have penetrated the Earth's mantle.

The Decorah impact may be one of several meteoric events that occurred around the same time, approximately 469 million years ago. This period is theorized to have experienced a cluster of impacts, including three other confirmed craters: the Rock Elm crater in Wisconsin, the Slate Islands crater in Lake Superior, and the Ames crater in Oklahoma. The sediments within the Decorah crater, specifically the Middle Ordovician Winneshiek Lagerstätte, have yielded a diverse array of unusual fossil fauna. Among these discoveries is Pentecopterus decorahensis, a newly identified species of eurypterid (sea scorpion) that was the largest known predator of its time, measuring nearly six feet in length. The species name was directly derived from the name of the nearby city, Decorah.