Weathering, erosion and deposition are slow processes that shape Earth’s surface over time. Wherever there is erosion, somewhere else sediment accumulates as an outpouring.
Chemical weathering creates karst landscapes where limestone dissolves to form sinkholes and caves, while iron oxide oxidation causes rocks to become rusty over time.
Water, wind, gravity, and biological activity combine to erode rocks on Earth’s surface; this process is known as weathering; parts of rocks wear away while fragments remain behind on the ground surface. Rivers in particular cause considerable erosion.
Physical weathering alters a rock’s shape but does not alter its chemical composition. It wears away rock edges, smoothes their surfaces and causes cracks and crevices to form while carrying small particles down slopes to form sand and gravel (Figure 9-12). Physical weathering processes play a dominant role in near surface environments (Figure 9-12).
Physical weathering is usually caused by wetting and drying cycles such as daily heating/cooling cycles or freezing/thawing events. Plant roots also play a part in physical weathering by growing into cracks in rocks where their roots expand further, breaking apart rocks apart as their expansion causes more cracks to form – this process is called bioerosion, and can sculpt landscape features like the Grand Canyon while creating unusual shapes like hoodoos.
Erosion refers to the process of breaking down and moving soil particles by natural forces such as water, wind and glacial ice; chemical and biological weathering also contributes to erosion. Erosion produces sediment which ranges from large rocks to microscopic dust particles.
Chemical weathering is the process by which rocks and minerals erode, often through chemical reactions with rainwater containing carbon dioxide dissolved into rocks or mineral surfaces that erodes or weakens them.
Mechanical weathering refers to the process of breaking and moving rocks through physical means. This may involve processes like erosional grinding as fast-moving river waters break apart boulders and sand into smaller pieces or when plant roots penetrate rocks to break them apart, but can also occur when water enters cracks in rocks and freezes later, or when earthquakes pulverize the terrain causing more rocks to crumble away.
Chemical weathering of limestone and chalk produces a material called gypsum that is very fine and white in texture, made up of marine organism skeletons and shells.
Over time, plant roots and animals break down rocks and soil. Their actions also accelerate other weathering processes that contribute to erosion.
Lichens and fungi indirectly assist rock weathering by altering surface temperatures through oxalic acid secretion, and increasing mineral dissolution through hyphal penetration. Other biophysical mechanisms that contribute to rock weathering include turgor pressure generation and calcium extraction from rock surfaces.
Wind erosion is a powerful force capable of wearing down and transporting rocks, such as boulders and sand, from their native places and depositing them elsewhere. This process polishes rock faces into smooth surfaces reminiscent of those found at Utah’s Arches National Park – giving rise to their name.
Though it is sometimes possible to distinguish abiotic from biotic processes, isolating their individual effects can often prove challenging. This is particularly true when considering biological weathering as biochemical and biophysical phenomena are closely interlinked; an example would be how lichen secretions of oxalic acid can erode sandstone through dissolution and weaken its microstructure.
Scotts Bluff National Monument’s bluffs are constantly changing due to weathering and erosion, with visitors witnessing its effects through rock slides as well as signs such as sand and gravel in river beds and surrounding rocks.
Human activities also play an integral part in shaping physical and chemical weathering in a region. For instance, fossil fuel burning creates high levels of sulphur dioxide in the atmosphere which then results in acid rain which corrodes rocks and materials that otherwise survive weathering processes.
Other human activities also affect how quickly and thoroughly erosion takes place, and what types of material it erodes away. For instance, those living in poverty are at greater risk due to less time spent outdoors and eating foods low in essential nutrients that lead to poor health outcomes like heart disease, diabetes and high blood pressure – factors known as social erosion.