Astrophysics/Space Physics Seminar
Mr. Ray Anderson; Iowa Geological Survey
“Iowa’s Meteorite Impact Structures; Manson and Decorah”
Abstract: About 71.4 million years ago an asteroid about 1¼ mile in diameter struck Iowa producing one of the largest known impact structures on Earth. The largely uneroded Manson Impact Structure, lies buried beneath glacial till in a 415 square miles area of Calhoun, Pocahontas, Webster, and Humboldt counties in north-central Iowa. The crater was investigated by research drilling during the early 1990s as a part of the search for the site of the impact that killed more than 95% of every living thing on Earth (most notably the dinosaurs) at the end of Cretaceous period. Less than 10 years ago a second, much smaller, and much older impact structure was identified below the northeast Iowa town of Decorah. The Decorah Impact Structure is almost entirely buried by limestone and other rocks, but much of its fascinating history has already been discovered by geologists.