lecture 2: weathering

• weathering

  disintegration or alteration of rock in its natural or original position at or near the Earth’s surface through physical, chemical, and biological processes induced or modified by wind, water, and climate.
• weathering

  involves physical, chemical, and biological processes acting separately or, more often, together to achieve the disintegration and decay of rock material.
• weathering

  is the process that breaks down rocks
• erosion

  breaks rocks down further and then moves them. 
• erosion

  is the process by which soil and rock particles are worn away and moved elsewhere by gravity, or by a moving transport agent – wind, water or ice.
• Weathering degrades a rock without changing its location. Erosion, on the other hand, causes rocks -- or particles of rock -- to be carried away from their original locations and deposited elsewhere.
• frost weathering

  occurs in areas where temperatures are below-zero. This is particularly common in Alpine areas and around the edges of glaciers. When water freezes, it expands, so when liquid water seeps into a crevice in the rock or soil and freezes, its expansion can cause deeper cracks in the rock and eventually break pieces off.
• thermal stress

  occurs when heat absorbed from the surrounding air causes a rock to expand. This expansion, and the subsequent contraction when the rock eventually cools, can cause thin sheets of the rock's outer layer to peel off. This can cause thin sheets of the rock's outer layer to peel off. This process is often found in desert areas, where temperatures vary greatly between day and night.
• salt wedging

  caused by water. Water can get into the rock in a number of ways. Unlike frost weathering, in this case the water evaporates, leaving behind salt, which eventually forms into crystals. The growing crystals can exert a pressure on the rock that eventually breaks it.
• frost wedging

  Water, while passing over rock surfaces, can freeze in depressions. The ice thus formed exerts pressure on the rocks, leading to cracks and weathering.
• temperature pressure

  Each area has varying temperature and pressure conditions. This fluctuation leads to the constant expansion and contraction in rocks. This reduces the strength of the rocks, which further breaks them down.
• oxidation

  The simplest definition of this type of weathering is the formation of rust when rock is exposed to air. Rust refers to the reaction of iron with oxygen and water. This reaction changes the color of the rocks to red.
• sinkhole

  When a certain part of the rock lying below the ground wears out due to chemical weathering, the entire rock above it caves it, thus creating a hole.
• plants

  are known to have their roots deep in the ground. These roots sometimes grow through rocks, leading to development of cracks in them.
• weathering by wind

  carries sand particles while traversing from one place to another. These particles are abrasive in nature. They hit the rocks, thus imparting shape to them. This type of weathering happens when the rock or soil contains thin or no plant cover. If plants are present, they hold up the soil firmly.
• weathering by water

  usually breaks down rocks or boulders. The resulting sediments then flow along with the river until they are deposited. At times, running water deposits salt crystals into the rocks. 
• causes of weathering

  • frost weathering
  • thermal stress
  • salt wedging
  • frost wedging
  • temperature-pressure
  • oxidation
  • sinkhole
  • decay
  • plants
  • by wind
  • by water
• decay

  Plants and animals are known to produce gases such as carbon dioxide on decomposition. However, this gas mixes with water, and the resultant compound produced is carbonic acid.
• types of weathering

  • mechanical/physical weathering
  • chemical weathering
  • biological/organic weathering
• mechanical/physical weathering

  is the breakdown of mineral or rock material by entirely mechanical methods brought about by a variety of causes. Some of the forces originate within the rock or mineral, while others are applied externally. Both of these stresses lead to strain and the rupture of the rock. The processes that may cause mechanical rupture are abrasion, crystallization, thermal insulation, wetting and drying, and pressure release.
• mechanical/physical weathering

  • frost wedging
  • thermal expansion
  • unloading
  • crystallization of salts
• frost wedging

  rock breakdown caused by expansion of ice in cracks and joints
• thermal expansion

  results from the expansion and contraction of rock, caused by temperature changes.
• unloading

  overlying materials (not necessarily on rocks) are removed which causes underlying rocks to expand and fracture parallel to the surface.
• crystallization of salts

  as result of dissolved salts expanding as they dry split rocks and honeycomb its surface.
• chemical weathering

  • hydrolysis
  • oxidation
  • reduction
  • hydration
  • carbonation
  • solution
• hydrolysis

  is the weathering reaction that occurs when the two surfaces of water and compound meet.
• oxidation

  is the reaction that occurs between compounds and oxygen.
• reduction

  is simply the reverse oxidation, and is thus caused by the addition of one or more electrons producing a more stable compound.
• hydration

  attachment of water molecules to crystalline structure of a rock causing expansion and weakness.
• carbonation

  is the reaction of carbonate and bicarbonate ions with minerals. The formation of carbonates usually takes place as a result of other chemical processes.
• solution

  process by which rocks is dissolved in water
• biological weathering

  It involves the disintegration of rock and mineral due to the chemical and or physical agents of an organism. The types of organisms that cause weathering range from bacteria to plants to animals.
• factors affecting the rate of weathering

  • endogenetic process
  • exogenetic process
• endogenetic process

  • rock type and composition
  • surface area
• exogenetic process

  • climate
  • topography
  • human activity