DAVID PARKER / SCIENCE PHOTO LIBRARY DAVID PARKER / SCIENCE PHOTO LIBRARY
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the state of Arizona, US. It is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile. Nearly two billion years of the Earth's geological history have been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted. While the specific geologic processes and timing that formed the Grand Canyon are the subject of debate by geologists, recent evidence suggests the Colorado River established its course through the canyon at least 17 million years ago. Cumulonimbus clouds are characterized by a flat, anvil-like top, caused by straight line winds at the higher altitudes which shear off the top of the cloud, as well as by an inversion over the thunderstorm caused by rising temperatures above the tropopause.
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