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Erosional Processes
Marine and Subaerial Processes that erode the coastline
Term | Description |
---|---|
Freeze-thaw | water collects in the cracks; water freezes and expands, melts and contracts; repeated expanding and contracting results in progressive weakening of the rock; this is most effective in cool maritime climates |
Heating and Cooling | thermal expansion and contraction of rock in daily cycle of heating and cooling; different crystals in the rock cause uneven contraction which sets up stresses in the rock |
Wetting and Drying | minerals such as montmorillonite in clay rocks expand and contract due to wetting and drying, causing stresses in the rock |
Crystal Growth | saline water enters cracks in the rock and evaporates, leading to the growth of salt crystals (e.g. sodium carbonate and magnesium sulphate); growing crystals prise the rock apart |
Hydrolysis | hydrogen ions from water react with minerals in the rock, causing it to disintegrate; this is common in granite; reactive ions are removed |
Hydration | water is absorbed, causing structural changes in certain mineral crystals (e.g. calcium sulphate becomes softer); absorption causes rocks to swell, creating stress |
Carbonation | hydrogen carbonate reacts with calcium carbonate from limestone and sedimentary rocks to form calcium bicarbonate which readily dissolves |
Solution | some minerals readily dissolve in sea water (e.g. halite - the mineral form of NaCl) |
Oxidation | some minerals react with oxygen (e.g. Fe2+ is oxidised to form Fe3+, leading to the collapse of its molecular structure) |