Encyclopedic Entry

The Grand Canyon, brought to you by the Colorado Plateau and the Colorado River.

Photograph by Sam Barberie, MyShot

Valles Marineris
The largest canyon in the solar system isn't found on Earth. Valles Marineris is a canyon system on Mars that is 4,000 kilometers (2,485 miles) long, 600 kilometers (372 miles) wide, and, in some places, 10 kilometers (6 miles) deep.

The Grand Canyon, in contrast, is 447 kilometers (277 miles) long, 29 kilometers (18 miles) wide, and 1.8 kilometers (6,000 feet) deep.

Surf's Down!
Surfing is much more than just "riding the waves"it starts with what lies beneath. The seafloor transforms ordinary waves into good waves . . . and good waves into great surfing. Bathymetry, or measuring the depth and rise of the seafloor, is important to good surfers.

If there is a steep ascent of the ocean floor near the beach, it will cause waves to rise more quickly, and become bigger. If, however, the ocean floor has a slow and gradual ascent, the waves will come in more slowly, and not break as big.

The famous El Porto surf area off the coast of Los Angeles, California, is a good example of how big waves develop. An underwater canyon focuses the energy of underwater currents, and the canyon's steep walls cause waves to rise quickly, producing huge, powerful waves.

A canyon is a deep, narrow valley with steep sides. “Canyon” comes from the Spanish word cañon, which means “tube” or “pipe.” The term “gorge” is often used to mean “canyon,” but a gorge is almost always steeper and narrower than a canyon.

The movement of rivers, the processes of weathering and erosion, and tectonic activity create canyons.

River Canyons

The most familiar type of canyon is probably the river canyon. The water pressure of a river can cut deep into a river bed. Sediments from the river bed are carried downstream, creating a deep, narrow channel.

Rivers that lie at the bottom of deep canyons are known as entrenched rivers. They are entrenched because, unlike rivers in wide, flat flood plains, they do not meander and change their course.

The Yarlung Zangbo Grand Canyon in Tibet, a region of southwestern China, was formed over millions of years by the Yarlung Zangbo River. This canyon is the deepest in the world—at some points extending more than 5,300 meters (17,490 feet) from top to bottom. Yarlung Zangbo Canyon is also one of the world’s longest canyons, at about 500 kilometers (310 miles).

Weathering and Erosion

Weathering and erosion also contribute to the formation of canyons. In winter, water seeps into cracks in the rock. This water freezes. As water freezes, it expands and turns into ice. Ice forces the cracks to become larger and larger, eroding bits of stone in the process. During brief, heavy rains, water rushes down the cracks, eroding even more rocks and stone. As more rocks crumble and fall, the canyon grows wider at the top than at the bottom.

When this process happens in soft rock, such as sandstone, it can lead to the development of slot canyons. Slot canyons are very narrow and deep. Sometimes, a slot canyon can be less than a meter (3 feet) wide, but hundreds of meters deep. Slot canyons can be dangerous. Their sides are usually very smooth and difficult to climb.

Some canyons with hard, underlying rock may develop cliffs and ledges after their softer, surface rock erodes. These ledges look like giant steps.

Sometimes, entire civilizations can develop on and around these canyon ledges. Native American nations, such as the Hopi and Sinagua, made cliff dwellings. Cliff dwellings were apartment-style shelters that housed hundreds of people. The shaded, elevated ledges in Walnut Canyon and Canyon de Chelly, in Arizona, provided protection from hostile neighbors and the burning desert sun.

Hard-rock canyons that are open at one end are called box canyons. The Hopi and Navajo people often used box canyons as natural corrals for sheep and cattle. They simply built a gate on the open side of the box canyon, and closed it when the animals were inside.

Limestone is a type of hard rock often found in canyons. Sometimes, limestone erodes and forms caves beneath the earth. As the ceilings of these caves collapse, canyons form. The Yorkshire Dales, an area in northern England, is a collection of river valleys and canyons created by limestone cave collapses.


Tectonic Uplift

Canyons are also formed by tectonic activity. As tectonic plates beneath the Earth’s crust shift and collide, their movement can change the area’s landscape. Sometimes, tectonic activity causes an area of the Earth’s crust to rise higher than the surrounding land. This process is called tectonic uplift. Tectonic uplift can create plateaus and mountains. Rivers and glaciers that cut through these elevated areas of land create deep canyons.

The Grand Canyon, in the U.S. state of Arizona, is a product of tectonic uplift. The Grand Canyon, up to 447 kilometers (277 miles) long, 29 kilometers (18 miles) wide, and 1.8 kilometers (6,000 feet) deep, is the largest canyon in the United States. The Grand Canyon has been carved, over millions of years, as the Colorado River cuts through the Colorado Plateau. The Colorado Plateau is a large area that was elevated through tectonic uplift millions of years ago. Geologists debate the age of the canyon itself—it may be between 5 million and 70 million years old.

Canyons Reveal Earth’s History

Canyons are like silent journals of an area’s history over thousands or even millions of years. By studying the exposed layers of rock in a canyon wall, experts can learn about how the climate changed, what kind of organisms were alive at certain times, and perhaps even how the canyon may change in the future.

For example, geologists studying layers of rock in the Columbia River Gorge, in the U.S. states of Washington and Oregon, discovered that the oldest rocks there are at least 17 million years old. They also found out the rocks are dark-black basalt, made from hardened lava. From this, geologists determined that the rocks formed when volcanoes erupted and their lava spilled out onto the land. Over millions of years, the Columbia River and Ice Age glaciers cut through the area and exposed its volcanic beginnings.

Canyons are also important to paleontology, or the study of fossils. Fossils are often best preserved in dry, hot areas. Since canyons usually form under the same conditions, they are good places to examine fossils.

The layers of sediment revealed by a canyon can make it easier to date fossils. For example, a new area of dinosaur tracks was discovered in the U.S. state of Utah at Glen Canyon National Recreation Area in 2009. These tracks reveal new information about a group of dinosaurs called ornithopods. Paleontologists analyzed the layers of rock surrounding the fossils to estimate how old they were. These new dinosaur tracks show that ornithopods were alive 20 million years earlier than scientists thought.

Geologists study canyons to determine how the landscape will change in the future. The erosion patterns and thickness of different layers can reveal the climate during different years. A series of very dry years will have very thin layers of rock, when little erosion took place. The overall pattern of erosion and layering reveals the rate of water flow, from both the river and rain, through a canyon.

Geologists estimate that the Grand Canyon, for example, is being eroded at a rate of 0.3 meters (1 foot) every 200 years. The Colorado Plateau, the geologic area where the Grand Canyon is located, is a very stable area. Geologists expect the Grand Canyon to continue to deepen as long as the Colorado River flows.


Submarine Canyons

Some of the deepest canyons lie beneath the ocean. These submarine canyons cut into continental shelves and continental slopes—the edges of continents that are underwater.

Some submarine canyons were carved by rivers that flowed during periods when the sea level was lower, and the continental shelves were exposed. The Hudson Canyon extends 750 kilometers (450 miles) into the Atlantic Ocean, from the mouth of the Hudson River, in the U.S. states of New York and New Jersey. At least part of the Hudson Canyon was the river bed during the last ice age, when sea levels were much lower.

Submarine canyons can also develop when powerful ocean currents sweep away sediments. Just as rivers erode land, these currents carve deep canyons in the ocean floor. Strong currents of the Atlantic Ocean prevent Whittard Canyon, about 400 kilometers (248 miles) south of the coast of Ireland, from filling with sediment. Scientists studying Whittard Canyon believe glacial water mixed with seawater to rush into the submarine canyon thousands of years ago.

The formation of some submarine canyons is still a mystery. Monterey Canyon is a deep submarine canyon off the coast of the U.S. state of California. It has been compared to the Grand Canyon because of its size. It is 152 kilometers (95 miles) long and 3.2 kilometers (2 miles) deep at its deepest point. Geologists still aren’t certain how Monterey Canyon was formed. One theory is that the canyon was formed by an ancient outlet of the Sacramento or Colorado Rivers. Another theory is that it was formed by tectonic activity—an earthquake splitting apart the rock with enormous force. Scientists believe the canyon was formed 25 million to 30 million years ago.

The depth of submarine canyons makes them hard to explore. Scientists usually use remotely operated vehicles (ROVs) to conduct studies. Sometimes, they can use a submersible, a special kind of submarine. The Monterey Bay Aquarium Research Institute (MBARI) uses a vehicle called Ventana to explore Monterey Canyon. Through the Ventana and other research vehicles, MBARI scientists have discovered new species of organisms living in the canyon, from tiny sea anemones to giant squid.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

ancient

Adjective

very old.

basalt

Noun

type of dark volcanic rock.

box canyon

Noun

deep canyon with an opening only on one side.

canyon

Noun

deep, narrow valley with steep sides.

Encyclopedic Entry: canyon

cattle

Noun

cows and oxen.

cave

Noun

underground chamber that opens to the surface. Cave entrances can be on land or in water.

channel

Noun

waterway between two relatively close land masses.

Encyclopedic Entry: channel

civilization

Noun

complex way of life that developed as humans began to develop urban settlements.

Encyclopedic Entry: civilization

cliff

Noun

steep wall of rock, earth, or ice.

Encyclopedic Entry: cliff

climate

Noun

all weather conditions for a given location over a period of time.

Encyclopedic Entry: climate

continent

Noun

one of the seven main land masses on Earth.

Encyclopedic Entry: continent

continental shelf

Noun

part of a continent that extends underwater to the deep-ocean floor.

Encyclopedic Entry: continental shelf

continental slope

Noun

the sometimes-steep descent of a continental shelf to the ocean floor.

corral

Noun

enclosed area, usually for livestock.

crust

Noun

rocky outermost layer of Earth or other planet.

Encyclopedic Entry: crust

current

Noun

steady, predictable flow of fluid within a larger body of that fluid.

Encyclopedic Entry: current

dale

Noun

wide valley.

desert

Noun

area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.

Encyclopedic Entry: desert

determine

Verb

to decide.

dinosaur

Noun

very large, extinct reptile chiefly from the Mesozoic Era, 251 million to 65 million years ago.

downstream

Noun

in the direction of a flow, toward its end.

durable

Adjective

strong and long-lasting.

dwelling

Noun

a place to live.

earthquake

Noun

the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

elevate

Verb

to raise higher than the surrounding area.

entrenched river

Noun

river with no flood plain, whose flow of water is trapped by the walls of a valley or gorge.

erosion

Noun

act in which earth is worn away, often by water, wind, or ice.

Encyclopedic Entry: erosion

estimate

Verb

to guess based on knowledge of the situation or object.

expand

Verb

to grow.

flood plain

Noun

flat area alongside a stream or river that is subject to flooding.

Encyclopedic Entry: flood plain

fossil

Noun

remnant, impression, or trace of an ancient organism.

Encyclopedic Entry: fossil

geologist

Noun

person who studies the physical formations of the Earth.

giant squid

Noun

deep-sea animal that can grow up to 12 meters (40 feet) long.

glacier

Noun

mass of ice that moves slowly over land.

Encyclopedic Entry: glacier

gorge

Noun

deep, narrow valley with steep sides, usually smaller than a canyon.

Encyclopedic Entry: gorge

Grand Canyon

Noun

large gorge made by the Colorado River in the U.S. state of Arizona.

Hopi

Noun

people and culture native to the southwestern U.S.

hostile

Adjective

confrontational or unfriendly.

ice

Noun

water in its solid form.

Encyclopedic Entry: ice

Ice Age

Noun

last glacial period, which peaked about 20,000 years ago.

landscape

Noun

the geographic features of a region.

Encyclopedic Entry: landscape

lava

Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

limestone

Noun

type of sedimentary rock mostly made of calcium carbonate from shells and skeletons of marine organisms.

meander

Verb

to wander aimlessly.

Monterey Bay Aquarium Research Institute (MBARI)

Noun

organization with a mission to pursue advanced research and education in ocean science and technology.

Native American

Noun

person whose ancestors were native inhabitants of North or South America. Native American usually does not include Eskimo or Hawaiian people.

Navajo

Noun

people and culture native to the southwestern United States.

paleontology

Noun

the study of fossils and life from early geologic periods.

Encyclopedic Entry: paleontology

plateau

Noun

large region that is higher than the surrounding area and relatively flat.

Encyclopedic Entry: plateau

river

Noun

large stream of flowing fresh water.

Encyclopedic Entry: river

river bed

Noun

material at the bottom of a river.

ROV

Noun

remotely operated vehicle.

sandstone

Noun

rock formed by grains of sand.

sea anemone

Noun

type of marine animal related to corals and jellies.

sea level

Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

Encyclopedic Entry: sea level

seawater

Noun

salty water from an ocean or sea.

sediment

Noun

solid material transported and deposited by water, ice, and wind.

Encyclopedic Entry: sediment

seep

Verb

to slowly flow through a border.

Sinagua

Noun

people and culture native to the southwestern U.S. who flourished between the 1100s-1400s.

slot canyon

Noun

very narrow, deep valley caused by water rushing through soft rock.

steep

Adjective

extreme incline or decline.

submarine

Noun

vehicle that can travel underwater.

submarine canyon

Noun

underwater valley formed by eroding streams of muddy water through which sediment ultimately reaches and spreads across the flat abyssal plains of the ocean floor.

submersible

Noun

small submarine used for research and exploration.

tectonic activity

Noun

movement of tectonic plates resulting in geologic activity such as volcanic eruptions and earthquakes.

tectonic plate

Noun

large, moveable segment of the Earth's crust.

tectonic uplift

Noun

movement of plates beneath the Earth's surface that causes one part of the landscape to rise higher than the surrounding area.

Valles Marineris

Noun

largest canyon in the solar system, found along the equator of Mars.

valley

Noun

depression in the Earth between hills.

volcano

Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

weathering

Noun

the breaking down or dissolving of the Earth's surface rocks and minerals.

Encyclopedic Entry: weathering

Credits

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Writers

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrators

Tim Gunther
Mary Crooks, National Geographic Society

Editors

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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