The Earth Gallery, The Continents, The North America Geographical Wonders: The Meteor Impact Craters, SSS: NNN, FFF. A Wayƒarer′s Story & Photo Gallery

After a few million years of erosion, most of the Bidahochi Formation has been removed from the Petrified Forest National Park area, leaving volcanic scoria cones and maars (flat-bottom, roughly circular volcanic craters of explosive origin). The vent from one of these maars is exposed on the Painted Desert Rim across the park road to the east of Pintado Point. The Hopi Butte Volcanic Field, which can be seen from the northern overlooks of the park extending northwest, is considered one of the largest concentrations of maar landforms in the world, covering about 965 square miles (2,500 square km). The erosion-resistant lava flows, such as Pilot Rock and the Hopi Buttes, protect the softer lake-bed deposits beneath.

An impact crater is a depression in the surface of a solid celestial body which has been formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have a raised rim with one or more floors that are lower in elevation than the surrounding terrain. Impact craters are typically circular, though they can be elliptical in shape or even irregular due to events such as landslides. Impact craters range in size from microscopic craters seen on lunar rocks returned by the Apollo Program, to simple bowl-shaped depressions and vast, complex, multi-ringed impact basins. Meteor Crater, (also known as Barrington Crater located near Winslow, Arizona) is a well-known example of a small impact crater on Earth.

On celestial bodies that experience active surface geological processes, such as Earth, Venus, Europa, Io, Titan, and Triton, visible impact craters are less common because they often over time become eroded, buried or transformed by tetonic and/or volcanic forces.

On such celestial bodies that experience such active processes which have destroyed much of the original crater topography, the terms impact structure or astrobleme, which is a word from the Greek meaning star-wound, are more commonly used.

Currently, on an average, Earth experiences one to three impacts large enough to create a 12 mile crater every one million year. This rate indicates that there should be far more relatively young craters on this planet than have been discovered so far. Thus, the lack of these young craters that are visible could indicate many have impacted the oceans and few of these undersea craters have been discovered due to the difficulty of surveying the sea floor, as well as the subduction of the ocean floor into interior of the Earth by plate tectonics.