• cliff
    Steep coastal cliffs can keep out invaders.

    Photograph by James P. Blair

    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.

    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.
  • Term Part of Speech Definition Encyclopedic Entry
    alluvium Noun

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

    canyon Noun

    deep, narrow valley with steep sides.

    Encyclopedic Entry: canyon
    cliff Noun

    steep wall of rock, earth, or ice.

    Encyclopedic Entry: cliff
    coast Noun

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

    Encyclopedic Entry: coast
    erosion Noun

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

    Encyclopedic Entry: erosion
    face Noun

    mountain cliff.

    landscape Noun

    the geographic features of a region.

    Encyclopedic Entry: landscape
    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.

    sediment Noun

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

    Encyclopedic Entry: sediment
    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.

    waterfall Noun

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

    Encyclopedic Entry: waterfall
    weathering Noun

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

    Encyclopedic Entry: weathering
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