Soil is essential to the life-support systems on Earth, yet careless or ignorant human activity can destroy it. One method of this destruction is by salt expansion – an activity similar to frost wedging.
Cementation transforms loose sediment into hard, lithified rock by using silica-rich cementing minerals such as calcite or chert.
Erosion occurs when rivers pass over land, carrying sediment that forms bits of sand and rock with it.
Erosion is a physical process caused by water, gravity, wind (see Chapter 10, Wind and Glaciers) or ice (see Chapter 14, Mass Wasting) that transports sediments from their source location to be deposited elsewhere. Liquid water acts as the principal agent of erosion.
Some types of rocks weather faster than others due to having different levels of erosion resistance. The rocks with the highest resistance form distinguishable geological features like Grand Canyon’s cliffs or Bryce Canyon National Park’s hoodoos; other features are formed using less resistant rocks forming valleys like this U-shaped valley seen here.
Ice can erode rocks by freezing and expanding within cracks, crevices, and crevasses, known as “ice wedging”.
Liquid water and ice are powerful agents of physical erosion, capable of washing particles off rock surfaces, washing away sediment build-up from places it had built up, and collapsing or breaking apart rocks into smaller ones.
Weathering and erosion have played a pivotal role in shaping our planet for billions of years. Acting like a geological cycle, erosion wears down Earth’s surface through wind, water, ice, plants and gravity, eventually depositing smaller pieces of rock or soil elsewhere – these processes are known as deposition and erosion respectively.
Over thousands of years, wind and water have created the Earth’s landscape through erosion. Erosion breaks rocks down into smaller pieces while moving particles to another location to be deposited there. The rate at which erosion takes place varies depending on factors like rock type, rainfall volume, land shape and shape of terrain.
Hard rocks like granite erode slowly while sandstone erodes quickly; plants help minimize weathering and erosion impacts.
River erosion is one of the primary forces at work on Earth. It transports sediment such as sand, silt and boulders across its path from place to place.
Biological weathering occurs when living organisms cause physical changes. For instance, burrowing animals create bioclimatic weathering by pushing rocks apart with their burrowing bodies, while tree roots also wedge rocks apart as they spread roots out.
Water wedging is another form of physical weathering. When water seeps into cracks in rock and freezes, expanding into wider spaces. Over time this action may break apart the rock entirely causing potholes on roads to form; road crews frequently have to repair these potholes in order to continue operating safely.
As weathering breaks down rock, its tiny pieces are transported away through erosion caused by gravity, running water, glaciers, waves, wind and deposition – eventually being left on beaches or far off river valleys as new deposits.
Salt expansion is a chemical weathering process that causes cracks to form in rocks, frequently seen in arid regions and salty seashores. Tafonis form when salt water evaporates away, leaving square imprints behind when it evaporates away from these locations.
Mechanical and chemical weathering of rocks depends on their crystallization rank in the Bowen Reaction Series (see Chapter 4, Igneous Rock and Volcanic Processes). Minerals with higher crystallization ranks experience less chemical weathering.
Geologists use sorted sediments to study erosion and transport processes. Well-sorted sediment indicates the influence of wind, glaciers or flowing water while poorly-sorted suggests rapid flooding or glacial scour erosion. Indoor pure salt expansion tests on silty clay with various compaction efforts and levels of salt/water content were conducted successfully.