Weathering

• Exogenic processes are the geological phenomena and processes which occur on and originate from the Earth's surface.
• Weathering is the breakdown of the materials of Earth’s crust into smaller pieces.
• Physical or Mechanical Weathering is a process by which rocks are broken down into smaller pieces by external conditions.
• Types of Physical weathering include Frost wedging, Salt Crystal Growth, Abrasion, Exfoliation/Unloading, Biological Activities, Friction and impact, Temperature changes.
• Frost Wedging is caused by the freezing and thawing of water that seeps into cracks of rocks, expanding water as it freezes slowly breaks up this sedimentary rock into unusual shapes.
• Salt crystal growth is a force exerted by salt crystal that formed as water evaporates from pore spaces or cracks in rocks can cause the rock to fall apart.
• Abrasion is caused by the rubbing and/or bouncing of rocks with each other.
• Exfoliation/ Unloading is the peeling away of large sheets of loosened rock materials.
• Biological activities are caused by an organism’s activity, examples include plant roots, burrowing of animals.
• Friction and Repeated Impact are caused by the rubbing and/or bouncing of rocks with each other.
• Weathering by the wind occurs as the wind blows it picks up small particles of sand and blasts large rocks with the abrasive particles, cutting and shaping the rock.
• Weathering by running water occurs when water in waterfalls, rivers and streams move over rock, the rocks are weathered—broken into smaller and smaller pieces.
• Weathering by glaciers occurs as a glacier is a large, river of ice that moves very slowly downhill.
• Chemical Weathering is the process that breaks down rock through chemical changes.
• Dissolution is the dissociation of molecules into ions such as dissolution of limestone in acidic water.
• Oxidation is the reaction of oxygen with other elements, for example, rusting of iron.
• Hydrolysis is the reaction of water with other elements, for example, weathering of rock by dissolving it.
• Living organisms, such as lichens, produce weak acids that chemically weather rock.
• Acid rain causes very rapid chemical weathering.
• Climate affects the rate, type and extent of weathering, areas that are cold and dry tend to have slow rates of chemical weathering and weathering is mostly physical; chemical weathering is most active in areas with high temperature and rainfall.
• Rock type affects the rate, type and extent of weathering, the minerals that constitute rocks have different susceptibilities to weathering.
• Rock structure affects the rate of weathering, the presence of joints, folds, faults, bedding planes through which agents of weathering enter a rock mass.
• Topography affects the rate of physical weathering, weathering occurs more quickly on a steep slope than on a gentle one.
• Time determines the degree of weathering of a rock, the longer time of exposure to agents of weathering results to higher rate of weathering.