Wind cannot carry as large particles as flowing water, but easily pick ups dry particles of soil, sand and dust and carries them away. Abrasion is the process of erosion produced by the suspended particles that impact on solid objects. Windblown grains of sand, carried along at high speed, are a very effective tool that can sandblast away rocks by abrasion.
Wind causes the lifting and transport of lighter particles from a dry soil, leaving behind a surface of coarse grained sand and rocks. One example is called frost action or frost shattering. Water gets into cracks and joints in bedrock. When the water freezes it expands and the cracks are opened a little wider.
Over time pieces of rock can split off a rock face and big boulders are broken into smaller rocks and gravel. Chemical weathering decomposes or decays rocks and minerals. Such moving water is among the most powerful of nature's landscape-altering tools. Weathering and erosion slowly chisel, polish, and buff Earth's rock into ever evolving works of art—and then wash the remains into the sea. The processes are definitively independent, but not exclusive.
Weathering is the mechanical and chemical hammer that breaks down and sculpts the rocks. Erosion transports the fragments away. Working together they create and reveal marvels of nature from tumbling boulders high in the mountains to sandstone arches in the parched desert to polished cliffs braced against violent seas.
Water is nature's most versatile tool. For example, take rain on a frigid day. The water pools in cracks and crevices. Then, at night, the temperature drops and the water expands as it turns to ice, splitting the rock like a sledgehammer to a wedge. The next day, under the beating sun, the ice melts and trickles the cracked fragments away.
Repeated swings in temperature can also weaken and eventually fragment rock, which expands when hot and shrinks when cold.
Such pulsing slowly turns stones in the arid desert to sand. Likewise, constant cycles from wet to dry will crumble clay. Bits of sand are picked up and carried off by the wind, which can then blast the sides of nearby rocks, buffing and polishing them smooth. These processes cause rocks to dislodge from hillsides and crumble as they tumble down a slope. Plant growth can also contribute to physical erosion in a process called bioerosion. Plants break up earthen materials as they take root, and can create cracks and crevice s in rocks they encounter.
Ice and liquid water can also contribute to physical erosion as their movement forces rocks to crash together or crack apart. Some rocks shatter and crumble, while others are worn away. River rocks are often much smoother than rocks found elsewhere, for instance, because they have been eroded by constant contact with other river rocks. Liquid water is the major agent of erosion on Earth. Rain, rivers, floods, lakes, and the ocean carry away bits of soil and sand and slowly wash away the sediment.
Rainfall produces four types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. Gullies carry water for brief periods of time during rainfall or snowmelt but appear as small valley s or crevasse s during dry season s. Valley erosion is the process in which rushing stream s and rivers wear away their bank s, creating larger and larger valleys.
The Fish River Canyon, in southern Namibia, is the largest canyon in Africa and a product of valley erosion. Over millions of years, the Fish River wore away at the hard gneiss bedrock, carving a canyon about kilometers 99 miles in length, 27 kilometers 17 miles wide, and meters 1, feet deep.
The ocean is a huge force of erosion. Coastal erosion —the wearing away of rocks, earth, or sand on the beach—can change the shape of entire coastlines. During the process of coastal erosion, waves pound rocks into pebbles and pebbles into sand. Wave s and current s sometimes transport sand away from beach es, moving the coastline farther inland. Coastal erosion can have a huge impact on human settlement as well as coastal ecosystem s.
The Cape Hatteras Lighthouse, for example, was nearly destroyed by coastal erosion. At the time, the lighthouse was nearly meters 1, feet from the ocean. Over time, the ocean eroded most of the beach near the lighthouse. By , the pounding surf was just 37 meters feet away and endanger ed the structure. Many people thought the lighthouse would collapse during a strong storm. Instead, thanks to a significant engineering feat completed in , it was moved meters 2, feet inland. The battering force of ocean waves also erodes seaside cliff s.
The action of erosion can create an array of coastal landscape features. For example, erosion can bore holes that form cave s. When water breaks through the back of the cave, it can create an arch.
The continual pounding of waves can cause the top of the arch to fall, leaving nothing but rock columns called sea stack s. The seven remaining sea stacks of Twelve Apostles Marine National Park, in Victoria, Australia, are among the most dramatic and well-known of these features of coastal erosion. Wind is a powerful agent of erosion. Aeolian wind-driven processes constantly transport dust, sand, and ash from one place to another. Wind can sometimes blow sand into towering dune s.
Some sand dune s in the Badain Jaran section of the Gobi Desert in China, for example, reach more than meters 1, feet high. In dry areas, windblown sand can blast against a rock with tremendous force, slowly wearing away the soft rock. Wind can also erode material until little remains at all. Ventifact s are rocks that have been sculpted by wind erosion. The enormous chalk formations in the White Desert of Egypt are ventifacts carved by thousands of years of wind roaring through the flat landscape.
Ice, usually in the form of glaciers, can erode the earth and create dramatic landforms. In frigid areas and on some mountaintops, glaciers move slowly downhill and across the land. As they move, they transport everything in their path, from tiny grains of sand to huge boulders. Rocks carried by glaciers scrape against the ground below, eroding both the ground and the rocks.
In this way, glaciers grind up rocks and scrape away the soil. Moving glaciers gouge out basin s and form steep-sided mountain valleys. Eroded sediment called moraine is often visible on and around glaciers. These glacial periods are known as ice age s. Ice Age glaciers carved much of the modern northern North American and European landscape. Ice Age glaciers scoured the ground to form what are now the Finger Lakes in the U.
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