Visited the town of Manson, Iowa, today.  This is a farm community nestled in the flat, corn-carpeted central Iowa countryside. Manson is situated over an extraordinary geological formation that is completely invisible from the surface.  Also called the “Manson Anomaly”, this location is the site of a meteor impact ca 74 million years ago. The Manson site was originally thought to be the source of the K-T boundary, but now it is recognized to have been formed ca 9 million years prior to the K-T event. Approximately 130 distinct impact craters have been identified.

The formation contains many of the classic features attributed to an impact crater and it has been studied at length.  Fortunately, the library in Manson has a collection of literature on the formation as well as a collection of core samples from about 10 bore locations. 

The impactor is thought to be a stoney meteor approximately 2 km in diameter.  According to the Iowa Geologic Survey, the crater structure is 37 km in diameter and sits under 20 to 70 m of glacial till.  It is believed that the terrain was covered by seawater at the time of impact and that the crater was filled with water fairly soon after the impact. 

What is interesting for this writer is that the Manson Crater is directly under the place I lived as a child.  Who knew that under the plain, flat, farmland were the remains of a large-scale calamity.  Things are never as they seem.  That’s what I really dig about science.