Wind is a major geological agent that causes erosion, transportation, and deposition. The three types of erosive work by wind are deflation, abrasion, and attrition. Deflation involves the removal of sand and dust particles, creating depressions called oases or desert pavement surfaces called hammadas. Abrasion occurs when wind carries sand and dust, grinding and polishing rock surfaces to form landforms like yardangs, pedestal rocks, and ventifacts. Transportation by wind moves loose materials through suspension, saltation, or rolling. Depositional features formed by wind include migrating dunes and loess deposits of wind-blown silt. Engineering in dune and loess areas requires stabilizing structures and treating

1. GEOLOGICAL AGENTS & THEIR
ACTION
Kaustubh J. Sane
HJD Institute of Technical
Education and Research, Kera

2. Geological agents
GEOLOGICAL
AGENTS
WIND
RIVER SEA
GROUNDWATER GLACIERS

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.

6. 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.

7. • 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.

9. • 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.

11. 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

12. Depositional features
• Dunes:
– It is a broadly conical heap of sand characterized
with two slope either side of a medial ridge or
crest.

14. Verhar (Pakistan)

16. 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.

19. 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.