Weathering agents

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  • 1. GEOLOGICAL AGENTS & THEIR ACTION Kaustubh J. Sane HJD Institute of Technical Education and Research, Kera
  • 3. WORK OF WIND • The wind acts in three different ways viz. Erosion, Transportation, Deposition. • Erosive work of wind: – Three types • Deflation • Abrasion • Attrition
  • 4. Deflation • The removal of sand particles and dust by strong wind is called deflation. • This is observed mainly in desert regions. • In some deserts deflation may remove the sand from a particular location and create a depressions. • These depressions some times reaches the ground water table. These deeper water filled depressions are called as OASES. • Wind deflation also produces another feature like HAMMADA. It is bare rock surface which is called as desert pavement.
  • 5. Wind Abrasion • Wind when consist of sand and dust particles it becomes powerful agent. • These type of erosion evolves rubbing, grinding, polishing and abrading of rock surface by wind is called wind abrasion. • These type of process itself is responsible for formation of various landforms viz. Yardangs, pedestal rocks, ventifacts.
  • 6. • Yardangs: • These are elongated, low- lying ridges forming overhangs above depression. • These are formed in areas where rocks of alternate hard and soft characters are lying above one another with gentle slope. • Pedestal rocks: • These are also called as mashroom rocks. • These are flat topped rock masses with narrow bottom.
  • 7. • Ventifacts: • These are small size rock fragments having one, two three or more polished surfaces. • The polishing of surface is carried out by prolonged action of wind. • As soon as polishing of one surface is achieved the rock is overturned by strong wind and again second face gets under action of wind. • These wind polished and facetted fragments are called ventifacts.
  • 8. Transportation Most Effective in Moving Loose Material • Suspension (Silt) – Light silt grade particles are lifted up in to upper layer and moves along with it. • Saltation (Sand) • Rolling
  • 9. Depositional features • Dunes: – It is a broadly conical heap of sand characterized with two slope either side of a medial ridge or crest.
  • 10. Verhar (Pakistan)
  • 11. Loess • Term is used for wind blown deposits of silt and clay. • Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micro-metre size range. • It is usually homogeneous and highly porous and is traversed by vertical capillaries.
  • 12. Engineering consideration • Dunes and loess offer complicated problem in construction. • As dunes & loess are migrating they are moving structures. • Methods applied in such conditions are; – Establishing frontal belts of vegetation that can resist the advancing of sand dunes. – Construction of wind breakers around the area. These walls check the velocities of approaching wind. – Treating the sands locally with crude oil. – In loess soil engineering problems is to deal with hydro consolidation characteristics of soil. – As loess soil gets settle down quickly in moisture, which is dangerous foundation soil.