GEOLOGICAL AGENTS & THEIR ACTION

Kaustubh J. Sane HJD Institute of Technical Education and Research, Kera

Geological agents

GEOLOGICAL AGENTS

WIND

RIVER SEA GROUNDWATER GLACIERS

WORK OF WIND

• The wind acts in three different ways viz. Erosion, Transportation, Deposition.

• Erosive work of wind:

– Three types

• Deflation

• Abrasion

• Attrition

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.

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.

• 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.

• 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.

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

Depositional features

• Dunes:

– It is a broadly conical heap of sand characterized with two slope either side of a medial ridge or crest.

Verhar (Pakistan)

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.

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.