To be the provider of geoscience data globally Navigation Main content Bottom links. What is geology? Rocks and minerals. Fossils and dinosaurs. Geology around the world. Over hundreds of years, it will completely disappear, but what happens over one year? What changes would you see figure 1? What forces of weathering wear down that road, or rocks or mountains over time?
Follow this link to view some animations of different types of weathering processes. Mechanical weathering also called physical weathering breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, just smaller. That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock.
There are many ways that rocks can be broken apart into smaller pieces. Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point figure 2. Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons.
Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside, as rock fragments separate and tumble down. Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Figure 3. Rocks on a beach are worn down by abrasion as passing waves cause them to strike each other. Abrasion makes rocks with sharp or jagged edges smooth and round. If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion figure 3.
Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering figure 4. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves. Figure 4. Mechanical weathering increases the rate of chemical weathering.
As rock breaks into smaller pieces, the surface area of the pieces increases figure 5. With more surfaces exposed, there are more surfaces on which chemical weathering can occur.
Figure 5. Mechanical weathering may increase the rate of chemical weathering. Chemical weathering is the other important type of weathering. Chemical weathering is different from mechanical weathering because the rock changes, not just in size of pieces, but in composition. That is, one type of mineral changes into a different mineral.
Chemical weathering works through chemical reactions that cause changes in the minerals. Most minerals form at high pressure or high temperatures deep in the crust, or sometimes in the mantle. A similar process, weathering , breaks down or dissolve s rock , but does not involve movement. Erosion is the opposite of deposition , the geological process in which earthen materials are deposited, or built up, on a landform. Most erosion is performed by liquid water, wind, or ice usually in the form of a glacier.
If the wind is dust y, or water or glacial ice is muddy, erosion is taking place. The brown color indicates that bits of rock and soil are suspended in the fluid air or water and being transported from one place to another.
This transported material is called sediment. Physical erosion describes the process of rocks changing their physical properties without changing their basic chemical composition.
Physical erosion often causes rocks to get smaller or smoother. Rocks erode d through physical erosion often form clastic sediments. Clastic sediment s are composed of fragments of older rocks that have been transported from their place of origin.
Landslide s and other forms of mass wasting are associated with physical weathering. 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. Why it's so hard to treat pain in infants. This wild African cat has adapted to life in a big city. Animals Wild Cities This wild African cat has adapted to life in a big city Caracals have learned to hunt around the urban edges of Cape Town, though the predator faces many threats, such as getting hit by cars.
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