Airborne geophysical survey of meteor crater under Decorah, Iowa. Image courtesy of Adam Kiel/U.S. Geological Survey
Air and ground surveys have allowed scientists to confirm the existence of a large meteoroid impact crater buried beneath a small town in Iowa in the US.
The 5.5 km wide crater under Decorah is the largest found in the US to date, with the site first hypothesized as a crater in 2008 when geologists noticed unknown shale deposits in cuttings from water wells drilled in the area. That hypothesis was then confirmed by an airborne geophysical survey and hydrology surveys.
Scientists estimate that the meteor that caused the crater had a diameter of around 230m and hit earth about 500 million years ago, with such meteors striking earth on average about once every 30,000 – 60,000 years.
