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Impact Craters: Terrestrial & Map

Instructor: Suzanne Rebert

Suzanne has taught college economics, geography, and statistics, and has master's degrees in agricultural economics and marine affairs (marine resource management).

Huge space rocks crash into our planet on a regular basis, and terrestrial impact craters are the evidence. Find out where you can see these craters, and why we don't see even more of them.

Definition

An impact crater is a landform left behind by the collision of a meteoroid, asteroid, or comet with a planet or moon. The classic crater is a bowl-shaped depression with a raised rim, but impact craters that have been eroded or filled over time can also be recognized by patterns of fault lines, mineral deposits, or through geophysical techniques, such as the mapping of gravitational or magnetic fields. Terrestrial impact craters are those found on Earth.

Barringer Crater, Arizona
Barringer Crater, Arizona

Many people, even those who have seen the famous Barringer Crater in Arizona or learned how an asteroid strike probably doomed the dinosaurs, might be surprised to learn that the Earth has been hit often -- in fact, more often than the Moon or Mars. Why don't we see huge craters everywhere? Sometimes the answer is that we're living right inside one! For example, Middleboro, Kentucky, Nördlingen, Germany, and the lower Delmarva Peninsula in Maryland all lie within impact craters.

Boundaries of the Chesapeake Bay impact crater
Map of Chesapeake Bay impact crater boundaries

Where Did They Go?

Most impact craters on Earth get disguised by the same forces that make this a living planet. Erosion wears down the crater's sides. Infilling happens when sediments, ice, windblown dust or other substances fill the depression and smooth out its contours. Volcanic activity can bury craters under layers of lava, and can also act as a decoy -- many impact craters look a lot like the craters of volcanoes, and that's what they were assumed to be until recent research proved otherwise. Tectonic forces, the movements of huge plates of Earth's crust, guarantee that ancient rocks that might hold impact evidence get subducted and 'recycled' on a regular basis. Finally, the fact that over 70 percent of Earth's surface is covered by oceans means that there's plenty of room for space rocks to hide under water.

Lake Manicouagan, Quebec, is an impact crater
Lake Manicouagan impact crater, Quebec

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