Download - 3 Unit-I Wind
-
8/11/2019 3 Unit-I Wind
1/35
GENERAL GEOLOGY
Unit - I
External agencies
WeatheringWind
River
Sea
Landslide
Internal agencies
Earthquakes
Plate tectonics
Groundwater
-
8/11/2019 3 Unit-I Wind
2/35
Wind
-
8/11/2019 3 Unit-I Wind
3/35
Introduction
Atmosphere is composed chiefly of gases
collectively known as air.
Air in motion is called wind
Wind is one of the major geological agents of
change on the surface
http://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpghttp://upload.wikimedia.org/wikipedia/en/1/13/Delicate_Arch_LaSalle.jpg -
8/11/2019 3 Unit-I Wind
4/35
-
8/11/2019 3 Unit-I Wind
5/35
[ORIGIN from Greek anemos wind] [ORIGIN from Greek baros weight]
-
8/11/2019 3 Unit-I Wind
6/35
Creates temporary or permanent changes on the
land surface depending on
wind volume,
wind velocity,
nature of the surface,
duration for which the wind blows etc. Strong winds blowing over loose ground, dry soils
and deserts may create many features within short
span of time
Wind acts as agent of erosion as a carrier fortransportation of particles and then deposit huge
quantitiesat different places.
-
8/11/2019 3 Unit-I Wind
7/35
Geological Work of Wind
1. Erosion Deflation
Abrasion
Attrition
2. Transportation Source of sediments
Methods of transport
The transporting power of wind
3. Deposition Dunes
Loess
-
8/11/2019 3 Unit-I Wind
8/35
1. Wind erosion Deflation
Abrasion
Attrition
-
8/11/2019 3 Unit-I Wind
9/35
Wind Deflation( To blow away)
Wind possesses not much erosive over the
ground covered with vegetation
Wind moving with sufficient velocity over dry
sands or bare ground covered with dust, its
remove huge quantity of the material from the
surface known as deflation
-
8/11/2019 3 Unit-I Wind
10/35
Wind Deflation
In some desert deflation may remove the sand from a particular
location and creates depression - virtually touching the water tableand such depression is known asBLOW OUTS.
Water filled depression known asOASIS is a place where vegetation
grows in desert
SLACK is another term used for depression created by
deflation
Ex :Quattara in western Egypt (Biggest slack)
-
8/11/2019 3 Unit-I Wind
11/35
Oasis
-
8/11/2019 3 Unit-I Wind
12/35
Wind Abrasion
Wind is a powerful agent for rubbing and
abrading the rock surfaces when naturally
loaded with sand & dust particles.
This type of erosion involves rubbing,
grinding, abrading and polishing of rock
surface by a natural agent known asAbrasion
-
8/11/2019 3 Unit-I Wind
13/35
Responsible for features of erosion
Yardangs
Pedestal rocksVentifacts
Desert pavements
Wind Abrasion
-
8/11/2019 3 Unit-I Wind
14/35
Yardangs It is an elongated low lying ridges forming
overhangs above depression. Trend is parallel to the prevailing wind
Yardangs are formed in area where rocks of
alternate hard and soft rock lying one over otherwith gentle slope.
-
8/11/2019 3 Unit-I Wind
15/35
Pedestal Rocks It is known as mushroom rocks
They flat topped rock masses
that are characterized with
slender lower region The top is commonly referred
as overhang and the support as
pedestal. They are generally
few meters in height
Overhang
Pedestal
Same rock
but affected
unevenly
-
8/11/2019 3 Unit-I Wind
16/35
-
8/11/2019 3 Unit-I Wind
17/35
Small sized rock fragments having
one, two, three or more polished
faces The polishing of the sides of the
originally rough fragments is
carried out by prolonged wind
abrasion on the surface of each
fragment.
Ventifacts
After one faces is plashed a
second face is made available tothe wind action by overturning of
the fragments during gushes of
wind
These wind polished & facetted
fragments are called ventifacts.
http://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpg -
8/11/2019 3 Unit-I Wind
18/35
It is flat rock surfaces covered by rounded or sub
rounded pebbles spread all over them & are typicalfeatures of rock deserts.
Pebbeles - distinguishing feature of desert
pavements. These pebbles may get further polished with time
and even acquire thin filmy oxides of Iron &
manganese.
This coated pebbles give a characteristic brow, dark
red or even black appearance to the desert
pavements.
http://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpghttp://upload.wikimedia.org/wikipedia/en/c/c7/Desert_Pavement_Mojave_2000.jpg -
8/11/2019 3 Unit-I Wind
19/35
Wind Attrition
The sand grains and other particles that arelifted by the winds and carried away do not
travel in a straight path
Their path is determined by their density andvelocity of the wind
It moves in Zig-Zag paths
The wear & tear of load sedimentssuffered by wind due to mutual impacts
during transport is Attrition
-
8/11/2019 3 Unit-I Wind
20/35
The above processes depends on
i. Nature of the Region
ii. Velocity of Windiii. Duration
Wind Attrition
-
8/11/2019 3 Unit-I Wind
21/35
2. Transportation Source of sediments
Methods of transport
The transporting power of wind
-
8/11/2019 3 Unit-I Wind
22/35
Source of Sediments
Sand, Silt, Clay (huge volumethousands of tons a day)
Sand deserts and freshly ploughed fields
Abrasive action over the rock surface
-
8/11/2019 3 Unit-I Wind
23/35
Methods of transport
Suspension Thelight and silt grade particlesmay be lifted high up in
the upper regions of the wind and moved along with it is
known as transport insuspension
Because the particles once lifted are not allowed to reston ground again and again unless they are finally
deposited.
Saltation:
The heavier and coarse sediments such as pebbles,gravels and sand grains are lifted up only for short
distance (up to 2m).
This type of sediment transport by wind issaltation.
-
8/11/2019 3 Unit-I Wind
24/35
Transporting power of Wind
Depends on velocity of wind
Particle size, shape and density.
-
8/11/2019 3 Unit-I Wind
25/35
-
8/11/2019 3 Unit-I Wind
26/35
Dunes
Variously shaped deposits of sand-gradeparticles accumulated by winds.
Gentle windward and steep leeward
-
8/11/2019 3 Unit-I Wind
27/35
A sand dune is defined as a broadly
conical heap of sand characterized with
two slopes on either side of a medial
ridge or crest
Sand dunes show great variation in their
shape, size & gropingtype of dunes.
1. The Cresentic Dunes
2. The Sigmoidal Dunes
3. Transverse Dunes
-
8/11/2019 3 Unit-I Wind
28/35
1. Crescent dunes:
It is characterized with two slopes in such a
way that the windward slope is convex andrise gently between 7 and 20
The slip face starts from the crest and is quite steepand concave in outline.
-
8/11/2019 3 Unit-I Wind
29/35
Simple type of cresentic dunes
typically half moon shape Developed by wind blowing in
the same direction for
considerable length of time
Barchans
-
8/11/2019 3 Unit-I Wind
30/35
2. The sigmoildal dune:
It is characterized with the absence of horns or
cups and a curved outline A sigmoidal dune is a s`teep sided ridge that
extends in a s-sheped outline
Both the sides of the sigmoidal dune are steeply
inclined at angle b/w 25to 32
Longitudinal dunes are called as SEIFS.
-
8/11/2019 3 Unit-I Wind
31/35
-
8/11/2019 3 Unit-I Wind
32/35
Dune classification
Dunes are classified in to simple, compond
and complex
Simple : single dune
Compound : two of more dunes of same type
Complex : group of different types of dunes
L
-
8/11/2019 3 Unit-I Wind
33/35
Loess It is used for wind blown deposits of silt and clay grade
particles.
Unconsolidated, Unstratified and Porous
Size range (0.01 0.05mm in diameter) 40 %
Rest 60 % by silt and finer clay
Occur in China, North America and Europe.
Particles get accumulated due to precipitation
-
8/11/2019 3 Unit-I Wind
34/35
Engineering considerations
Protecting the bui l t-up areas and agr icul tur al
lands
movements of sand dunes
M ethods for combating and advancing sands:
1. Establ ishi ng f r ontal tr acts or belt of vegetation that can
resist the advancing sands by checking the velocity of wind
2. Constru ction of win d breaks or wall saround the area to
be protected.
3. Treating the sands locall y with cr ude oil whereby theirsusceptibil ity for transpor t by wind is consider ably
reduced
L oess soi ls ar e ver y danger ous f or
foundation
-
8/11/2019 3 Unit-I Wind
35/35