Meteor Crater in Arizona is a good example of a simple impact crater. This crater is about 1,200 meters in diameter and 170 meters deep. The crater rim rises nearly 80 meters about the surrounding plain. The crater was formed between 20,000 and 50,000 years ago by the impact of an iron meteorite weighing over over 60,000 tons. The photograph of Meteor Crater at the top of this page was taken by David Roddy of the United States Geological Survey.
Complex craters are larger in diameter but shallower in depth.
Gravity collapses the crater walls downward and inward. A central peak may form when the crater floor rebounds from the impact. To become complex, a crater must have a large enough diameter. On Earth the transition diameter lies between two and four kilometers. This eight kilometer diameter crater is about 280 million years old.