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Rocks & weathering lesson 4
- 2. Weathering The decomposition anddisintegration of rocks in situ.
- 3. Decomposition Refers to chemical weatheringand creates changes in rock substances For Example: Granite decompose into clay
- 4. 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
- 5. Erosion • Is thebreaking down and removal of rocks • agents of erosion such as rivers, glaciers and the sea
- 6.
- 7. Regolith • a layerof 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.
- 9. • Weathering anderosion 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
- 10. Three Types ofWeathering 1. Physical Weathering 2. Chemical Weathering 3. Biological Weathering
- 11. Physical Weathering • Disintegrationof 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
- 12. Four main typesof Physical / Mechanical Weathering 1. Freeze-thaw action / Frost Shattering / Ice crystal Growth 2. Salt crystalisation 3. Granular disintegration /Exfoliation 4. Pressure release
- 13. Freeze thaw action 1. When water within Continuation the cracks of alternate freezes to freezing and ice, its thawing will volume cause joints expands as and pores much 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.
- 17. Factors encouraging FrostShattering / 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
- 18. 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.
- 19. Salt weathering ofbuilding Salt weathering of sandstone near stone on the island of Gozo, Qobustan, Azerbaijan. Malta
- 20. 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)
- 23. Pressure release • Itis 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
- 24. Pressure release: • commonin 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.
- 26. What type ofweathering? W
- 27. What type ofweathering?
- 28. What type ofphysical weathering?
- 29. Classwork • Ross pg51 – Noting activity