Weathering is the physical process by which rocks erode away into smaller and smaller pieces over time, creating the “weathered effect.” The effect typically works slowly over longer timeframes.
Ice can creep into cracks in rocks and serve as a wedge to split them open, while changes in temperature weaken it and turn it to dust. Wind may transport bits of rock around to new locations – carving out features like the Grand Canyon in its wake.
Water
Water is one of the primary agents in weathering erosion. It plays a key role in creating chemical sedimentary rock, as well as transporting them through erosion processes like mass wasting (see Chapter 10, Mass Wasting), gravity, and glaciers (see Chapter 14, Glaciers).
Air pollution often results in water being evaporated from oceans, lakes, vegetation and forests evaporating and then returning as rain or snow onto Earth, carrying with it erosion products, decayed vegetation and microorganisms as well as dissolved chemicals like salts and mineral ions that have leached out through soil layers (horizon A and B) onto which rainwater penetrates quickly, leaching most soluble chemicals out.
Erosion can happen quickly in the form of mudslides or rocks sliding off mountains, or slowly as water wears away at cliff faces. Either way, it has helped shape some amazing landforms on Earth while at times carrying harmful pollutants into water sources like rivers and lakes.
Ice
Over billions of years, water, ice, plants, gravity and weathering have combined forces to shape Earth’s landscape into what we see today. These forces work like an ever-evolving form of erosion to move rocks to new locations through physical means or chemical alteration.
Erosion occurs either slowly, as in the case of glaciers moving across mountains, or quickly with mudslides. Once carried away by erosion, tiny pieces of rock that were carried away eventually settle somewhere else through deposition; this could be local like at Split Apple Rock in New Zealand or farther away like when debris is carried by river to lakes.
Ice can be an extremely powerful force that can break apart rocks. Its freezing and expansion process widens cracks in rocks while its repeated cycles of freezing and melting wedge itself further into them – this process, known as “ice wedging”, often necessitates road crew repairs due to potholes caused by ice wedging.
Wind
Wind erosion can be an effective means of erosion. Its force can carry small particles such as silt and clay over long distances from one place to the next, often being more prevalent in arid regions than humid ones.
As erosion sweeps over Earth’s surface, it wears away rock fragments and transports them away. While this process usually occurs over thousands or millions of years, faster erosion rates may occur if a rock has particularly hard or rough surfaces.
Erosion can also be caused by living organisms, like plant roots that wedge between cracks in rocks or fish that break off chunks of rock while feeding on algae, but most erosion is the result of forces like water, wind, ice (glaciers) and gravity chiselling away at Earth’s rocks and shaping them into ever-evolving works of art – these forces that create canyons like the Grand Canyon as well as dunes in deserts as well as riverbed sandbars and rich delta soils in farmlands.
Gravity
As rocks break apart under weathering, their debris are transported away by erosion – an inexorably powerful process driven by forces such as water, wind, ice and gravity that carry it in its wake to new locations.
Chemical reactions in water, especially oxidation (rusting), loosen the bonds that hold rock together, making it softer and easier to break apart. This type of weathering happens most rapidly near rivers or oceans.
Water erosion can also help shape landscapes, creating waterfalls in places where hard, slowly-eroded rock meets with soft terrain that erodes more rapidly; then when water passes over that soft rock it wears it away forming canyons or ravines.
Erosion can also work to smoothen out sediment particles through rounding. This means that any sharp edges on the sediment have worn away over time while traveling from place to place, with greater energy exposure when more rounded particles exist in an environment.