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Any land area surrounded entirely by water is considered an island. The exception to this definition is a land area of continental size, such as Australia, which is considered a nation-continent. But Iceland, also a nation, is much smaller and is considered an island. Islands are found in oceans, seas, lakes, and rivers.

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aggtelek cavern altamira cave antiparos blue grotto capri carlsbad caverns caves and devil's hole fingal's geography jenolan kent's luray mammoth monumental mountain peak postojna singing wind national park world wyandotte interesting of the famous cavern|caves

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Interesting Caves and Caverns of the World

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The following list names interesting caves and caverns of the world, including Aggtelek in Hungary, Blue Grotto in Italy, Kent's Cavern in England, Mammoth Cave in Kentucky, Wind Cave in South Dakota, and more.

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Add your creative common license credits here!

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Example: World Geography Student Resources

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Students can use flickr to find pictures of these different kinds of land features and post them to this padlet wall!

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Valleys are depressed areas of land-scoured and washed out by the conspiring forces of gravity, water, and ice. Some hang; others are hollow. They all take the form of a "U" or "V."

Rivers and streams make most primary valley cuts, carving steep-walled sides and a narrow floor that from afar looks like the letter "V." The gradient of the river-how quickly it drops-helps define the steepness of the sides and the width of the floor. Mountain valleys, for example, tend to have near-vertical walls and a narrow channel, but out on the plains, the slopes are shallow and the channel is wide.

As waters wind toward the sea, they add to natural twists in the land by stripping sediment from the outsides of bends and dumping it on the insides. The bulk of the rock and dirt is dredged from the bottom of the channel, a process called down cutting that can ultimately lead to deep, slender chasms like Black Canyon in Colorado's Gunnison National Park.

Types of Valleys

Some river and stream valleys, especially those in the mountains or located near the North and South Poles, are transformed by glaciers.

The massive blocks of snow and ice slowly creep downhill where they will meet the least resistance: valleys already cut by rivers and streams. As the glaciers ooze, they pick up rocks and grind away at the valley floor and sides, pressing the "V" into a "U." When the glacier melts, a U-shaped valley marks the spot where the snow and ice once flowed.

Side valleys are formed by tributaries to streams and rivers and feed the main stem. Where the main channel is carved deeper than the tributary, as commonly occurs during glaciations, the side valleys are left hanging. Waterfalls often cascade from the outlet of the upper valley into the drainage below.

Hollows, like those in Appalachia, are small valleys nestled between mountains or hills.

Giant valleys, called rifts, are found where two pieces of Earth's crust are separated or split apart. One such example is the Great Rift Valley, a rift system stretching from the Middle East to southern Africa.

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black canyon of the gunnison national park

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Valleys are depressed areas of land-scoured and washed out by the conspiring forces of gravity, water, and ice. Some hang; others are hollow. They all take the form of a "U" or "V." Rivers and streams make most primary valley cuts, carving steep-walled sides and a narrow floor that from afar looks like the letter "V."

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Bound by cliffs and cut by erosion, canyons are deep, narrow valleys in the Earth's crust that evoke superlatives and a sense of wonder. Layers of rock outline stories of regional geology like the table of contents to a scientific text.

The landforms commonly break parched terrain where rivers are the major force that sculpts the land. They are also found on ocean floors where the currents dig underwater grooves.

"Grand" is the word used to describe one of the most famous canyons of all. Cut by the Colorado River over the last few million years, the Grand Canyon is 277 miles (446 kilometers) long, more than 5,000 feet (1,500 meters) deep, but only 18 miles (29 kilometers) across at its widest yawn.

Layers of rock in the Grand Canyon tell much about the Colorado Plateau's formative years: a mountain range built with two-billion-year-old rock and then eroded away; sediments deposited from an ancient sea; more mountains; more erosion; another sea; a burst of volcanic activity; and the birth of a river that has since carved the chasm by washing the layers away.

Each layer erodes differently. Some crumble into slopes, others sheer cliffs. They stack together like a leaning staircase that leads to the river's edge. A mixture of minerals gives each layer a distinctive hue of yellow, green, or red.

And its immense size has been seen by very few. More people have orbited the Earth than have hked the Grand Canyon from end to end. Follow the trek of Pete McBride and Kevin Fedarko using this interactive map.

Types of Canyons

Other canyons start where a spring sprouts from the base of a cliff. Such cliffs are composed of permeable, or porous, rock. Instead of flowing off the cliff, water seeps down into the rock until it hits an impermeable layer beneath and is forced to leak sideways. Where the water emerges, the cliff wall is weakened and eventually collapses. A box canyon forms as sections of wall collapse further and further back into the land. The heads of these canyons are marked by cliffs on at least three sides.

Slot canyons are narrow corridors sliced into eroding plateaus by periodic bursts of rushing water. Some measure less than a few feet across but drop several hundred feet to the floor.

Submarine canyons are similar to those on land in shape and form, but are cut by currents on the ocean floor. Many are the mere extension of a river canyon as it dumps into the ocean and flows across the continental shelf. Others are gouged from turbid currents that occasionally plunge to the ocean floor.

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Bound by cliffs and cut by erosion, canyons are deep, narrow valleys in the Earth's crust that evoke superlatives and a sense of wonder. Layers of rock outline stories of regional geology like the table of contents to a scientific text. The landforms commonly break parched terrain where rivers are the major force that sculpts the land.

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Rearrange the Locations of these land features!

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Rearrange the Locations of these land features!

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Drag each item to where you think the land feature would be located in the world!

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National Geographic: Stories of Animals, Nature, and Culture

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Explore National Geographic. A world leader in geography, cartography and exploration.