Weathering changes Earth’s rocks into striking geological features. When combined with erosion, its effects create unique geological formations like waterfalls, deltas, and beaches.
erosion leads to deposition – the process of depositing sediment elsewhere – which in turn creates features like meanders and oxbow lakes.
Physical
Weathering, or the physical disintegration of rocks and minerals on Earth’s surface, is affected by various environmental factors including temperature, water, oxygen and living organisms. Over time it changes landscape, soil composition and climate dramatically.
Mechanical weathering is the process by which rocks break into smaller pieces without altering their chemical makeup, occurring where their surfaces come into contact with each other through cracks or ledges. As more surface area is present on a rock, its rate of weathering increases proportionately.
Erosion is the process by which loose, decomposed rocks are carried away from their point of origin by forces such as water, wind and ice; over time this sediment settles in new locations. Different rocks exhibit differing levels of erosion resistance which result in distinctive geological features like those seen at Bryce Canyon National Park in Utah; more resistant rock takes longer to be broken down and eroded than its less resistant counterpart.
Chemical
Chemical weathering breaks apart the bonds holding rocks together, making it easier for other substances to wear away the rock surface. Water molecules use their polarity and hydrogen bonds to pry ions out of mineral crystal lattices and replace them with chemicals with lower binding energies – thus speeding up weathering processes more readily for minerals ranked higher on Bowen’s Reaction Series, such as quartz or feldspars, than for silica (SiO2).
Mechanical or chemical weathering produces sediments which are transported via erosion to various destinations for deposit. If these deposits become buried and compacted over time they become clastic sedimentary rock formations.
Sand is easily transported and deposited by fluid systems such as moving water or wind; other grains, like fine silt and clay, may stick more to other sediment or have weaker attractive forces between themselves and other particles, hindering their movement in these systems.
Biological
Biological weathering occurs when organisms like plants and lichen release organic acids onto rocks, dissolving minerals that compose them and dissolving limestone into cave systems and cliffs as acid rain from pollution caused by coal, oil and gas releases acid rain that further dissolves limestone through chemical weathering. Water also plays an important role in breaking down rock by wearing away mountain edges before carrying sediment downstream for deposit as deltas or beaches.
Gravity and glaciers transport materials that have been eroded to new locations, while gravity and glaciers transport eroded materials to different places on Earth. Together these forces chisel away at Earth’s rocks to form ever-shifting landscapes; over millions of years, these natural processes will continue shaping and molding our world in unpredictable ways.
Human Impact
Human activity can play a pivotal role in weathering erosion deposition in many ways. Paving over landscapes reduces vegetation cover, exposing soils to sunlight which accelerates chemical weathering processes. Meanwhile, adding concrete to rivers or streams alters their flow rate, increasing erosion rates and sediment transport rates while building dams can trap sediments to decrease erosion downstream areas.
Human industry produces gases which produce acid rain, which causes rocks to carbonate and disintegrate. Landslides and floods caused by rainwater flowing over these eroded rocks can damage buildings, crops and animals alike.
Researchers like USC assistant professor Mara Nutt use the Santa Ynez Mountains in southern California as an ideal laboratory to examine shale weathering and its influence on climate change. It provides consistent exposure of one shale unit with documented erosion rate gradients close to urbanization; plus natural variations in temperature and precipitation which allow scientists to compare long-term human impacts on erosion rates with natural geological features in an ecological system.