Weathering refers to the physical disintegration of rocks at Earth’s surface. Erosion refers to the process by which this loose rock fragments and modifications move across new locations; winds, water and ice are often effective agents of erosion.
Liquid or frozen (ice wedging) water can enter cracks in rock and expand to form wedges that break apart the stone’s structure, acting like an instrument for splitting it.
Mechanical Weathering
Plants and animals both contribute to mechanical weathering by forcing their roots into cracks in rocks, widening them out, and eventually breaking apart the rock (figure 5.1.6). Burrowing animals cause further mechanical weathering by physically altering soil or breaking apart rocks they dig through; additional heat or pressure changes such as when water freezes over cold temperatures, or immense pressure releases through an earthquake, can also break apart rocks (figure 5.1.7).
Abrasion is a form of mechanical weathering in which two rocks come into contact, often occurring during rockfalls from cliffs or glacier movements through valleys, as well as when windborne particles hit rocks; hence why many streets look as though someone pounded down hard on them – with its uneven, pitted surfaces making chemical weathering much simpler to occur.
Chemical Weathering
Chemical weathering of rocks involves many processes that interact between its minerals and external agents like air and water, altering its mineral composition and weakening them to allow more severe mechanical weathering processes to take place.
Water that comes into contact with igneous rock may cause some silicate minerals (like feldspar and quartz ) to react and form clay minerals or completely dissipate, contributing to sediment production in rivers, resulting in gravel- or pebble-rich river beds. This chemical weathering phenomenon is one major source of sediment production in rivers.
Chemical weathering occurs when rocks are exposed to environmental influences such as salt spray from the ocean or dripping water in caves that forms calcite crystals over time, leading to further erosion in their surroundings. This chemical process is an integral component of landscape erosion.
Acid Rain
Acid rain is precipitation with elevated concentrations of sulfuric or nitric acid that damages forests, rivers, lakes, rocks, and environmental resources. Furthermore, its acidity erodes man-made structures more rapidly than regular rainfall such as buildings, statues or tombstones.
Acid pollution results from burning fossil fuels and unethical waste disposal practices, with winds often carrying sulfur dioxide and nitrogen oxide gases for hundreds of miles before disseminating as acid rain or fog.
At Scotts Bluff National Monument, acid rain deprives soil of its ability to retain calcium, weakening and killing insects that summit-nest birds rely on for survival and reproduction. Furthermore, corrosion attacks metal structures and cars, wood rots away and concrete/stone building materials degrade; acidic particles also enter bodies of water where they leech nutrients that cause overgrowth suffocating fish or aquatic life altogether.
Natural Agents
Weathering erosion deposition is affected by various natural agents, from plants and animals contributing to mechanical weathering by growing roots that penetrate cracks in rocks causing them to widen and break – this process is known as abrasion.
Water, in both its liquid and frozen forms, is one of the primary natural agents responsible for both erosion and disintegration. It seeps through cracks in rocks to enlarge them while weakening bonds between grains of rock. Furthermore, freezing-thawing cycles cause this material to disintegrate further until eventually pieces begin breaking away and breaking off into separate pieces.
Streams, from rivulets to rivers, play an essential role in erosion and disintegration. They complete the hydrologic cycle by returning precipitation that falls on land back into oceans; transport sediment from their banks back onto their course, while also dismantling rock structures around their banks with their currents; flowing water can carry both weathered and unweathered material like pebbles, sand and gravel through a process known as attrition.