Weathering and erosion are ever present in our lives; from cracking roads and sidewalks as water expands to waves pounding rocks along beaches.
Weathering and erosion work together to sculpt Earth’s rocks into ever-evolving landforms; this process is known as geologic cycling.
Water
Weathering breaks rocks down into smaller pieces while erosion transports those pieces to new places.
Liquid water in the form of rain, rivers, and streams is one of the principal agents of erosion. It seeps into cracks and crevices in rocks, freezes and expands, leading to mechanical weathering; plant roots also contribute to mechanical weathering.
As water moves downstream it carries away erosion-affected particles that have become suspended in its streambed, depositing them as the B horizon, composed primarily of humus and mineral sediment that acts like a sponge to absorb air-borne chemicals that dissolve soluble chemicals, also known as “soluble chemicals”, to form what’s known as saprolite at the base of most soils.
Ice
Ice, whether in its liquid or solid state, is an extremely strong mechanical weathering agent. Liquid water that seeps through cracks in rock may freeze and expand into solid form as it freezes, acting like a wedge against its structure to split and fracture it; this process is known as frost weathering or cryo-fracturing and road crews often patch potholes formed due to it.
Glaciers are excellent at dislodging and transporting rocks and sediment, sculpting landscapes with U-shaped valleys, drumlins, and other landforms created by their movement.
Sediments formed through glacial erosion are similar to the sediments deposited by fluvial environments and include sand, silt, clay, gravel and larger clasts. However, due to pressure exerted from melting and refreeze ice on these rocks during erosion events they tend to be thicker and more heavily cemented than typical sedimentary rock layers.
Wind
Wind erosion is more prevalent in arid regions due to its powerful forces, carrying particles over long distances and picking up small silts and clays as it dismantles larger rocks into dust.
Scotts Bluff National Monument’s bluff has been formed through years of wind erosion. This process left ventifacts on its rock surface similar to ancient petroglyphs found on ancient cliff faces.
Wind erosion differs from water erosion by not flushing away particles that have been eroded; instead, it deposits them elsewhere – this process is known as deposition. Deposited material may end up nearby – such as on top of existing soil layers – or far away – such as another country. Human activity like burning coal or natural gas accelerates this process further and hinders plant growth while potentially harming our air quality.
Salt
Sediments are solid materials deposited from water, ice or wind that have been transported between locations by moving bodies of water, such as rivers. Sediments contain rocks, minerals and the remains of plants and animals that have fallen to Earth over time.
Weathering of rocks can alter their minerals through weathering processes, particularly chemical weathering. An example of chemical weathering would be acid rain produced from fossil fuel combustion which dissolves limestone or rusts metals such as iron.
Physical and mechanical weathering can also break down exposed rock surfaces. Clast corners (clasts) can also be worn down through rounding; well-rounded clasts are less likely to stick together and easier for transport in streams or rivers, aiding sediment flow quicker which ultimately shapes landscapes more quickly.
Plants and Animals
Rooted plants help prevent erosion by stabilizing soil with their roots. Furthermore, certain microorganisms release organic acids which break down minerals.
Physical weathering is a natural process that breaks rocks apart into smaller pieces. This may involve rock fracturing, freeze-thaw cycles and root wedges. Liquid water may seep into cracks in rocks before freezing and expanding when frozen; over time this causes those cracks to widen over time. Roots may invade rocks to cause mechanical weathering while burrowing animals also contribute to this type of weathering by tunneling underneath rocks.
Erosion occurs through transporting forces such as wind, water and ice that transport weathered materials to lower elevations where they can then settle into new locations; this process created the Grand Canyon over millions of years.