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What is the Rio Grande Rift?

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Mexico, Chihuahua, Rio Grande River and Sierra Rica
Robert Frerck/The Image Bank/Getty Images
Question: What is the Rio Grande Rift?
Answer: The Rio Grande rift is a geologic surface feature that is distinguished by an elongated valley. Rifts are formed when the earth's crust stretches and thins. Landforms caused by movement of the earth's crust are classified as tectonic. New Mexico is bisected by a north-south stretch of land that is caused by the Colorado Plateau pulling away from the High Plains, essentially creating a rift. The Rio Grande runs through the rift, and its course is controlled by the rift's shape and form.

The northern part of the Rio Grande rift is narrow and made of a series of basins flanked by mountains. The rift widens south of Socorro, and in the southern part of the state, it merges with the basin and range province of southwestern New Mexico, becoming quite wide.

Not all parts of the Rio Grande rift began pulling apart at the same time. The southern extension began drifting about 36 million years ago. In the north, the rift began forming about 26 million years ago.

What About Volcanoes?
When the crust began to pull apart, it triggered volcanism, or volcanic activity, in the area. Volcanic remains can be seen when looking west of Albuquerque, where their remains are quite evident. The Valles Caldera near Los Alamos is one of the world's youngest and largest calderas, created more than a million years ago by the collapse of a magma chamber.

What About Earthquakes?
There is evidence that large earthquakes occurred in south-central Colorado in the past 5,000 to 15,000 years. These earthquakes (7.0 magnitude or higher) not likely to occur although it is possible they will. Seismic activity in the region in New Mexico is low to moderate, with a slightly higher risk for occurrence in the rift regions.

Rifts cause topographic depressions that fill with sediments over time. The sediment basins of Albuquerque are over three miles thick.

Does the rift continue to widen today? Yes, but so slowly it won't be noticed. The rift moves about 0.5 and 2 millimeters per year.

The Rio Grande rift is geologically special. Very few rifts are found on land, with most formed along mid-ocean ridges. Other land rifts include the East African rift, sometimes called the Great Rift Valley, and Lake Baikal, which is a filled with lakes and located in Russia.

Where Can I Find Out More About the Rio Grande Rift?
The Rio Grande rift is one of the reasons New Mexico is so geologically special. To find out more about the geology of New Mexico, visit the New Mexico Museum of Natural History and Science. You'll find information about the state's geologic occurrences and ages, which are illustrated with maps, diagrams and more.

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