Exercise

3. Agents of Erosion

Q. 1) Complete the chain:

Agents Erosional landforms Depositional landforms

1) River
2) Wind
3) Sea waves
4) Groundwater
5) Glacier
Answer: -

Agents Erosional landforms Depositional landforms

1) River V- shaped valleys (Gorges, Alluvial Fans, Deltas, Flood
Canyons.), Waterfalls, Pot Plains, Natural Levees,
Holes, Structural Benches, Braided Channels, River
River Terraces, Meanders, Ox-Bow Lakes,
Peneplains,
2) Wind Pediplains, Deflation Sand dunes, Loess, Beaches,
Hollows, Mushroom Bars, spits, and Lagoons.
Tables, Cliffs, Terraces,
Caves, Stacks and Stumps
3) Sea waves Cliffs, Wave-Cut Platform, Beaches, Bars and Barriers,
Sea Caves, Coastal Wetlands, Sabkha.
4) Groundwater Corrasion or Abration, Alluvial Fans, Deltas
Corrosion or Solution,
Hydraulic Action (Valleys,
Gorges, Canyon) Potholes,
Plunge pools,
5) Glacier Cirque or Corris, Hanging Moraines, Eskers, Drumlins,
Valleys or U-shaped
Valleys, Fjords/fiords,
Horns and Aretes,

Q. 2) Choose the correct option by identifying the correct correlation

in the sentences:

1. Water or snow enters the cracks in the rocks and makes it weak. When
the glacier passes on these rocks, it pulls the rocks at the bottom along with
it. This process is called
a) Plucking b) Abrasion c) Attrition d) Transportation

2) Sometimes, the river starts erosion upstream. This happens when the
head stream gets a lot of water in the early stages of river’s flow.

a) Downcutting b) Headward erosion c) Lateral erosion d) Vertical erosion

3) Soft rock erodes beneath the hard rock due to sea waves. This results
into landforms which further develop as sea arches. The landform is

a) Sea cave b) sea stack c) sea cliff d) wave cut platform

4]This landform develops due to depositional work of wind. The windward

slope of this landform is gentle.

a) Loess plains b) barchans c) Seif d) Sand hills

Q.5) River, glacier, wind, sea waves and groundwater are the agents of
erosion. Following work in the correct order is responsible to form various
landforms.

a) Disintegration, picking up, transportation, weathering

b) picking up, disintegration, deposition, weathering

c) deposition, transportation, picking up, disintegration

d) disintegration, picking up, transportation, deposition

Q. 3) Give geographical reasons:

1) The Eastern coast of India have deltas formed by the rivers but the
Western coast has estuaries.

Ans.:- Hard Rocks of Western ghat don't allow Western flowing rivers to
widen their mouth into sea, so these rivers form Estuaries whereas Eastern
rivers flow through broken hills and mountain ranges. So, they are widened
and flow with lesser velocity before entering into sea.

2) There is direct relationship between the velocity of the agents and the
process of deposition.
Ans:- River current erodes the surface and those eroded particles later get
deposited and forming structures like Delta. When we see air, then we can
see how a sand dune shifts from one place to other by blowing of winds. In
both these cases we can see there is direct relationship between velocity of
agent and process of deposition.

3) Compared to all the agents, sea waves work ceaselessly.

Ans:- Among these geographical agents, the sea waves work ceaselessly
because, the oceans contain more than 90% of our planet's total water and
the wind flow. The wind pressure zones above this enormous amount of
water are almost constant. And that's why the sea waves are generated
almost in a continuous way, without any kind of break.

4) One finds many sheep rocks, horns, arêtes and hanging valleys in the
Himalayas.

Ans:- The Himalaya is the huge mountain belt that formed due to the
sinking of the Indo-Australian plate under the Eurasian plate. It is
comprised of rocks that are highly folded, faulted and fracture. It is marked
by the presence of features such as the horns, aretes and hanging valleys.

Aretes refers to those narrow ridges of rock that eventually separates two
distinct valleys.

In terms of geology, a horn is defined as the structure that forms when

glaciers weather and erodes three or more than three aretes, leaving out
only a sharp-edged peak.

The hanging valleys are defined as those shallow valleys that is cut by a
small glacier, as a result of which the height of these valley floors is higher
than the major valley that is cut by larger glaciers.

5) Karst landforms are seen concealed under the surface of the earth.

Ans:- Karst is a geography shaped from the disintegration of dissolvable

shakes, for example, limestone, dolomite, and gypsum. It is portrayed by
underground seepage frameworks with sinkholes and caverns.
Underground seepage may constrain surface water, with not many to no
waterways or lakes.
6) Snowline decides the limit of glacier work as an agent of erosion.

Ans:- The hydrosphere, liquid water, is the single most important agent of
erosion and deposition. ... Maximum extent of Laurentide Ice Sheet .... The
glacial budget works in a similar way.

Q. 4) Write short notes on:

1) Attrition

Ans:- Erosion is the wearing a way of rock along the coastline. Attrition -
this is when rocks that the sea is carrying knock against each other. They
break apart to become smaller and more rounded. Solution - this is when
sea water dissolves certain types of rocks.

Attrition happens when rocks and pebbles carried by the waves smash into
each other, wearing each other away and gradually becoming smaller,
rounder and smoother.

Erosion is the process that wears away the river bed and banks. Erosion
also breaks up the rocks that are carried by the river.

There are four types of erosion:

Hydraulic action, Abrasion, Attrition and Solution.

2) The work of rivers in hilly areas and human activities

Ans:- Rivers play an important role in the development of the landscape of

a region. The river water is the source of irrigation water for agriculture.
These rivers deposits sand, silt and clay making the soil of the region fertile.
This helps the human beings to grow more crops.

3) Conditions necessary for work of wind.

Ans:- A wind is formed as a result of flow of air from the area of high
pressure region to area of low pressure region. In this geographical region
"atmospheric pressure" is the most important and responsible factor to the
wind formation.

The difference of “atmospheric pressure” caused by the result of weather

forecasting. Due to this “atmospheric pressure” the air moves from high
pressure to low pressure. The closer of high and low pressure together are
gratitude and stronger pressure causes the formation of wind. The several
effects that cause the formation of the wind such as “earth’s rotation” and
the “solar energy” from the sun.

Q. 5) Distinguish between:
1) Attrition and Abrasion

Attrition Abrasion

Abrasion is a type of erosion where Attrition is a type of erosion which

the material being transported occurs very fast in comparison to
erodes away at a surface over time. abrasion. Generally, we consider it
This means the process of abrasion as a coastal or river erosion. During
is a slow erosion. The possible cause attrition, we can observe that the
for abrasion is the friction caused by objects travelling through a river
scuffing, scratching, wearing down, channel downstream can hit the
marring, rubbing away, etc. The river bed materials and break down
intensity of this process is the bed material into very small to
determined by the hardness, medium fragments.
concentration, velocity, and mass of
the material that is being eroded. In
contrast to attrition, abrasion
usually occurs due to the rubbing of
the surface against each other,
which results in wearing down of
one surface or both surfaces.

the process of abrasion occurs in During this process, the newly

four major ways: glaciation, coastal produced bed particles become
erosion, channel transport, and from round and smooth. Unlike in
the wind. Glaciation slowly grinds abrasion, where the rubbing of
rocks picked up by ice against rock surfaces causes the erosion, attrition
surfaces. In channel transport refers to hitting of surfaces which
abrasion, the surfaces of solid cause erosion. We can also observe
objects that travel through river attrition in glacial regions, where
channels cause erosion. Coastal abrasion takes place due to the
erosion is the abrasion caused by movement of ice with embedded
objects flowing in water due to boulders over surface sediments.
waves. The final method of abrasion
is the abrasion caused by sand and
small stones transported by the
wind.

2) U shaped valley and V shaped valley

U shaped valley V shaped valley

U-shaped valleys are casual by V-shaped valley are carved out by

glaciers in hilly regions. river in their youthful stages.

They are associated with hanging They are original in nature, i.e. they
valleys. are formed by the erosional actions
of the rivers.

Their shapes are that of the letter ‘U’ Their shapes are of the letter ‘V’ of
of the English alphabet. English alphabet.

They are modified forms of pre- They are associated with gorges,
existing valleys. canyon etc.
3) Stalactite and stalagmite

Stalactite stalagmite

It is a well-known fact that stalactite Stalagmite is regarded as the

and stalagmite formation can be deposition of the mounds of rocks
observed with key differences. over a period of time.

Both are related to the mineral

formation in caves.

It is an icicle shaped structure that For instance flow stones are

hangs from the ceiling of the cave. deposited due to the deposition of
the rocks by the strong gush of
water in an impeccable manner.

4) Tributaries and distributaries

Tributaries Distributaries

1. When a number of smaller rivers . When the main river breaks up into
join the main river, we call those as smaller streams, we get
tributaries. distributaries.

It may originate from glaciers, lakes 2. It is formed from the main river.
or springs.

3. Generally, it doesn't change its 3. It diverts from the main river in

course. the delta region.

4. Tributaries add water to the main 4. It takes away water from the main
river. river.

5. For example, Yamuna is a 5. They are numerous and do not

tributary of Ganga. have names.
Q. 6) Answer in detail:

1) Explain the landforms formed by different agents through the process of

abrasion.

Ans:- Sea waves have a great erosive force, In their role of an erosional agent they
perform four functions. When the sea water loaded with rock fragments and sand
attack the coastal rocks it is called abrasion.

Sea Cliffs: Steep rocky coast rising almost vertically above sea water is called sea cliff which
is very precipitous with overhanging crest. The steepness of true vertical cliffs depends on
variations of lithology and geological structure and relative rate of sub-aerial weathering and
erosion of cliff face and crest and marine erosion of cliff base.

Sea Caves: - Sea caves are formed along the coast due to gradual erosion of weak and
strongly jointed rocks by up-rushing breaker waves (surf currents). The joints are widened
into large cavities and hollows which are further enlarged due to gradual wave erosion into
well-developed coastal caves. Sea caves are more frequently formed in carbonate rocks
(mainly limestones and chalks) because they are eroded more by solution processes. It may
be pointed out that sea caves are not permanent features as they are very often destroyed by
up-rushing high-energy storm waves.

Sea Caves: -When the upper part of the coastal rock is hard and the lower part is soft, the
erosion is not uniform. The lower part of the rock in such circumstances is eroded much
faster than the upper part.

Sea Arches: When a part of coast extends to some distance into the sea, sea waves working
from opposite directions cut a passage through the soft rocks. In the initial stages, this assage
is a narrow hole but it enlarges into a broad arch.

Sea Stacks: When the roof of an arch is broken by erosion or under its own weight or due to
any other reason a part of the original rock remains standing as a solitary mass. It may be the
rock forming the side of the arch. This type of a feature is called a seastack, sometimes they
take the shape of islands but such islands are not permanent.

Work of Wind: - Abrasion: In the process of wind abrasion, wind drives sand and dust
particles against an exposed rock or soil surface.

Ventifacts are rocks that have been abraded, pitted, etched, grooved, or polished by wind-
driven sand or ice crystals. These geomorphic features are most typically found in arid
environments where there is little vegetation to interfere with aeolian particle transport,
where there are frequently strong winds, and where there is a steady but not overwhelming
supply of sand.

Mushroom Tables / Mushroom rocks are Ventifacts in the shape of a mushroom. In

deserts, a greater amount of sand and rock particles are transported close to the ground by the
winds which cause more bottom erosion in overlying rocks than the top. This result in the
formation of rock pillars shaped like a mushroom with narrow pillars with broad top surfaces.
Work of Glaciers:-

Cirque or Corrie: -They are deep, long and wide troughs or basins with very steep
concave to vertically dropping high walls at its head as well as sides, they are simply a bowl-
shaped depression formed due to the erosional activity of glaciers, when these depressions are
filled with water, they are called as Cirque lake or Corrie Lake or Tarn Lakes.

Hanging Valleys or U-shaped Valleys, Fjords/fiords: The Glacier doesn’t create a new
valley like a river does but deepens and widens a pre-existing valley by smoothening away
the irregularities. These valleys, which are formed by the glacial erosions assume the shape of
letter ‘U’ and hence are called as U-shaped Valleys or Hanging Valleys. A fjord is a very
deep glacial trough filled with sea water and making up shorelines. A fjord is formed when
a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock
and this valley gradually gets filled with the seawater (formed in mountains nearby sea).

Horns and Aretes: -Horns are sharp pointed and steep-sided peaks. They are formed by
headward erosion of cirque wall. When the divide between two cirque walls gets narrow
because of progressive erosions, it results in the formation of a saw-toothed ridge called
Arete.

2) Explain how the depositional work done by river Ganga has been
beneficial to human activities.

Ans:- River ganga deposits sand, silt, mud and other sediments called as alluvium at the
elevation land. This results in formation of green landform. This landform is the diversity of
vegetation. The delta of river ganga is the rich source of fish population.

Alluvial Fans:-

They are found in the middle course of a river at the foot of slope/
mountains. When the stream moves from the higher-level break into foot
slope plain of low gradient, it loses its energy needed to transport much of
its load. Thus, they get dumped and spread as a broad low to the high
cone-shaped deposits called an alluvial fan. The deposits are not roughly
very well sorted.

Deltas: - “Sunderban Deltas” are like an alluvial fan but develop at a

different location. They are found in the mouth of the river, which is the
final location of depositional activity of Ganga river. Unlike alluvial fans,
the deposits making up deltas are very well sorted with clear stratification.

3) Which agents of erosion can you see on the cover page of the textbook?
Which landforms can you see there? Write the process of formation of
anyone.
Ans:- answer in details in your own word

Q. 7) Draw neat and labelled diagrams for:

1) Deflation

2) Wave-cut platform
3) Mushroom rocks