Disintegration• Produces smaller, angular fragments of the same rocks, such as scree.• No change in chemical composition.• For example: Granite disintegrates into smaller fragment but rock type is still granite
Erosion• Is the breaking down and removal of rocks• agents of erosion such as rivers, glaciers and the sea
DenudationWeatheringand erosionworkingtogethercausinglandscape tobe worn down
Regolith• a layer of loose material covering solid rock.• It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.
• Weathering and erosion depend on each other• One could not exist very effectively without the other• Weathering break down a rock surface to produce a pile of loose debris (Regolith)• Erosion then removes the broken down rock fragments often using the ‘weathered fragments’ as ‘tools’ for erosion.• This exposes a fresh rock surface to the processes of weathering and so the two processes continue
Three Types of Weathering1. Physical Weathering2. Chemical Weathering3. Biological Weathering
Physical Weathering• Disintegration of rock into smaller particles by mechanical processes but without any change in the chemical composition of the rock• Where is it likely to occur? - devoid of vegetation - deserts, high mountains, arctic regions• End product- sands
Four main types of Physical / Mechanical Weathering1. Freeze-thaw action / Frost Shattering / Ice crystal Growth2. Salt crystalisation3. Granular disintegration /Exfoliation4. Pressure release
Freeze thaw action 1. Whenwater within Continuation the cracks of alternate freezes to freezing and ice, its thawing will volume cause jointsexpands as and poresmuch as 9%. enlarge and shatter. 2. This expansion creates a powerful force called frost action or freeze-thaw action, which can exceed the tensional strength of rock.
Factors encouraging Frost Shattering / Freeze Thaw action• Rapid freezing with a minimum temperature of -50C• Frequent cycle of freeze thaw actions• High degree of porosity or density of cracks in a rock• Presence of water
Salt-crystal growth (haloclasty)• causes disintegration of rocks• saline solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind.• salt crystals expand as they are heated up, exerting pressure on the confining rock.• may also take place when solutions decompose rocks• Example: limestone and chalk to form salt solutions of sodium sulfate or Sodium carbonate, when the moisture evaporates to form salt crystals.
Salt weathering of building Salt weathering of sandstone nearstone on the island of Gozo, Qobustan, Azerbaijan.Malta
Insolation weathering / heating and cooling• Expansion and contraction of rock particles resulting from extreme variations in temperature• Significant in desert area where diurnal temperature range is high (400C – 500C)
Pressure release• It is not caused by element of the weather. However, it does occur in situ• Involve the disintegration of rocks to expand• Pressure release can be caused: i. Erosion of overlying rock ii. When huge ice sheets melt at the end of a glacial period
Pressure release:• common in intrusive rocks that were formed deep under ground.• E.g. granite batholiths.• When this rock is exposed to the surface by uplift and erosion the rock expands and sheet joints form parallel to the rock surface.