A cliff is a mass of rock that rises very high and is almost vertical, or straight up-and-down. Cliffs are very common landscape features. They can form near the ocean (sea cliffs), high in mountains, or as the walls of canyons and valleys. Waterfalls tumble over cliffs.
 
Cliffs are usually formed because of processes called erosion and weathering. Weathering happens when natural events, like wind or rain, break up pieces of rock. In coastal areas, strong winds and powerful waves break off soft or grainy rocks from hardier rocks. The harder rocks are left as cliffs.
 
The tiny pieces of rocks broken off by weathering are called sediment or alluvium. Erosion is the process of transportation of this sediment. On sea cliffs, sediment becomes part of the seafloor and is washed away with the waves. On inland cliffs, sediment is often carried away by rivers or winds.
 
Larger rocks broken off by sediment are called scree or talus. Scree builds up at the bottom of many inland cliffs as rocks tumble down. These piles are called scree slopes or talus piles. Some scree slopes can be so large that soil and sediment can build up between the rocks, allowing trees and other vegetation to grow on the slope.
 
Most scientists and mountaineers think the Rupal Flank of Nanga Parbat, a mountain in the Himalayas, is the highest cliff in the world. The Rupal Flank rises 4,600 meters (15,092 feet) above its base. Others say the highest cliff in the world is the east face of Great Trango, in the Karakoram mountain range, which is 1,340 meters (4,396 feet) tall and one of the most difficult rock-climbs in the world. Both Nanga Parbat and Great Trango are located in Pakistan.
cliff
Steep coastal cliffs can keep out invaders.
Verona Rupes
Verona Rupes is a cliff on Miranda, a moon of Uranus. Verona Rupes is probably the tallest cliff in the solar system, rising as much as 10 kilometers (6.2 miles) from its base.

Don't Look Up
Some of the largest and steepest cliffs on Earth are actually found under water. These cliffs are sometimes called oceanic trenches.

alluvium
Noun

gravel, sand, and smaller materials deposited by flowing water.

Noun

deep, narrow valley with steep sides.

Noun

steep wall of rock, earth, or ice.

Noun

edge of land along the sea or other large body of water.

Noun

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

face
Noun

mountain cliff.

Noun

the geographic features of a region.

mountaineer
Noun

someone who climbs mountains.

rock
Noun

natural substance composed of solid mineral matter.

scree
Noun

accumulation of broken rocks, boulders, and other material at the base of cliffs or other tall rock formations.

Noun

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

valley
Noun

depression in the Earth between hills.

vegetation
Noun

all the plant life of a specific place.

vertical
Noun

up-down direction, or at a right angle to Earth and the horizon.

Noun

flow of water descending steeply over a cliff. Also called a cascade.

Noun

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