Weathering, or the breakdown of rock and mineral material on Earth’s surface, occurs naturally due to elements like water, ice, acids, salts, plants and animals as well as fluctuations in temperature.
Erosion occurs naturally and forms part of the natural landscape; for example, erosion carved the Grand Canyon.
Water is one of the primary agents of weathering. It plays an essential role in breaking down rocks and minerals by physical, chemical and biological means as well as playing an integral part in erosion that creates striking landscapes such as Uluru (Ayers Rock), Grand Canyon and glacial landscapes all over the globe.
Physical weathering involves breaking rocks apart without altering their chemical structure, usually through freezing and expanding of water within rock cracks or by tree roots that burrow beneath rocks. Physical weathering often precedes more serious forms of weathering like erosion.
Water transforms from liquid into solid when exposed to very cold temperatures; at -321 degrees Celsius (-196 degrees Fahrenheit), ice forms.
When warm air collides with very cold air, freezing precipitation such as sleet, snowflakes and glaciers forms.
Ice is an effective form of erosion that can transport rocks many miles from their original positions, an effect known as mass wasting.
Ice can induce chemical weathering through its freezing and thawing processes on rocks, cracking and disintegrating them through cryofracturing or mechanical weathering by tearing or scraping rocks – also known as exfoliation.
Chemical weathering disassembles minerals within rocks through chemical reactions involving water. Oxygen in surface water reacts with iron-bearing minerals to form rust, weakening them further so physical weathering can do its work more easily.
Carbon dioxide in the air reacts with water to form a weak acid that dissolves rock, creating caves such as Carlsbad Caverns in New Mexico.
Chemical weathering may also convert silicate minerals in igneous rocks into clays or oxidize them, and may erode away soft parts of sedimentary rocks.
Salty rocks form gravel and sand as they weather into gravel and sand over time, as is the ocean due to evaporation and melting ice reducing its freshness.
Salts exhibit a broad spectrum of properties. They can range from clear or opaque, brittle or crystalline forms; to being odorless or strongly flavored; even metallic in colorless form or metallic-lustrous finish. Furthermore, different salts may elicit all five basic tastes: salty (sodium chloride); sweet (lead diacetate, which should never be consumed); sour (potassium bitartrate); bitter (magnesium sulfate); umami or savory (monosodium glutamate).
Road crews and plow drivers frequently spread rock salt on roads when temperatures become cold, as this helps lower the freezing point of water, thus preventing it from condensing into ice crystals and forming on its surface.
Plants and their roots contribute significantly to mechanical weathering; as their roots enter cracks in rocks and wear away at them, causing it to crumble away. Plants also increase chemical weathering by producing acids which dissolve rocks and minerals quickly.
Chemical weathering occurs when rocks are exposed to air or water. Oxygen can oxidize minerals to produce alteration products while water can seep through rocks and soil to carry these materials to rivers or oceans for disposal.
Some minerals are more stable than others and won’t easily weather, such as quartz, olivine and K, Na-rich feldspars which are common components of clastic sedimentary rocks.
The landscape is constantly shifting. Weathering breaks down rocks and minerals present on Earth’s surface, followed by erosion transporting off their components.
Weathering can take thousands or millions of years. But in some instances it can occur more rapidly; for instance, the Grand Canyon was formed over time by flowing water.
Rocks are subject to wear-and-tear damage caused by physical, mechanical and chemical weathering processes; chemical or biological weathering processes also play a part. Plant roots often penetrate cracks in rocks and widen these cracks over time.
Moles and other underground burrowing animals as well as those which dig and trample aboveground, like rodents, can also play an integral role in breaking apart rocks. Animals also contribute to chemical weathering by producing carbonic acid or altering the molecular structures of rocks and soils, leading to chemical weathering processes which lead to chemical erosion of rocks and soils.