Canyon formation
Canyons can be created by erosion. They often occur in the upper courses of rivers, where the stream has a strong, swift current that erodes its valley rapidly. The largest and most famous canyons have been cut through dry or partly dry land by swift streams fed by rain or melting snow.
Canyons can also be formed by tectonic activity. Tectonic activity is large-scale, gradual upward and downward movements that occur within the Earth's crust. Some of the most striking canyons have been the result of this activity.
Other canyons are created by undersea activity. Deep canyons that extend down to the sea floor are called submarine canyons. Most of these canyons are V-shaped depressions with steep, rocky walls many thousands of feet high. The walls of the Grand Bahama Canyon—in the Atlantic Ocean off the islands of the Bahamas—are said to be the highest. They rise nearly 3 miles (5 kilometers) from the canyon floor.
Notable canyons
Perhaps the most famous canyon is the Grand Canyon in the U.S. state of Arizona. Formed by the Colorado River, the Grand Canyon is noted for its fantastic shapes and colors. It is as wide as 18 miles (29 kilometers) and as deep as a mile (1.6 kilometers). Other notable canyons in the United States are those of the Snake, Arkansas, Rio Grande, and Yellowstone rivers.