The Gist of NCERT - Geography

Geography 11

99

LAND FORMS

After weathering processes have had In the middle stages, streams cut their beds
their actions on the earth materials making slower, and lateral erosion of valley sides
up the surface of the earth, the geomorphic becomes severe. Gradually, the valley sides
agents like running water, ground water, are reduced to lower and lower slopes. The
wind, glaciers, waves perform erosion. divides between drainage basins are likewise
Erosion causes changes on the surface of the lowered until they are almost completely
earth. Deposition follows erosion and flattened leaving finally, a lowland of faint
because of deposition too, changes occur on relief with some low resistant remnants called
the surface of the earth. monad nocks standing out here and there.
This type of plain forming as a result of stream
A landmass passes through stages of erosion is called a peneplain (an almost plain).
development somewhat comparable to the The characteristics of each of the stages of
stages of life- youth, mature and old age. landscapes developing in running water
regimes may be summarized as follows:
Running Water
Youth
In humid regions, which receive heavy
rainfall running water is considered the most Streams are few during this stage with
important of the geomorphic agents in poor integration and flow over original
bringing about the degradation of the land slopes showing shallow V-shaped valleys
surface. There are two components of running with no floodplains or with very narrow
water. One is overland flow in general land floodplains along trunk streams. Streams
surface as a sheet. Another is linear flow as divides are broad and flat with marshes,
streams and rivers in valleys. Most of the swamp and lakes. Meanders if present
erosional landforms made by running water develop over these broad upland surfaces.
are associated with vigorous and youthful These meanders may eventually entrench
rivers flowing along gradients. With time, themselves into the uplands. Waterfalls and
stream channels over steep gradients turn rapids may exist where local hard rock bodies
gentler due to continued erosion, and as a are exposed.
consequence, lose their velocity, facilitating
active deposition. Mature

In the early stages, down-cutting During this stage streams are plenty
dominates during which irregularities such with good integration. The valleys are still
as waterfalls and cascades will be removed. V-shaped but deep; trunk streams are broad

100 Gist of NCERT (Geography)

enough to have wider floodplains within aided by the abrasion of rock fragments. Such
which streams may flow in meanders con- large and deep holes at the base of waterfalls
fined within the valley. The flat and broad are called plunge pools. These pools also help
inter stream areas and swamps and marshes in the deepening of valleys. Waterfalls are
of youth disappear and the stream divides also transitory like any other landform and
turn sharp. Waterfalls and rapids disappear. will recede gradually and bring the floor of
the valley above waterfalls to the level below.
Old
Incised or Entrenched Meanders
Smaller tributaries during old age are
few with gentle gradients. Streams meander But very deep and wide meanders
freely over vast floodplains showing natural found cut in hard rocks. Such meanders are
levees, oxbow lakes, etc. Divides are broad called incised or entrenched meanders.
and flat with lakes, swamps and marshes.
Most of the landscape is at or slightly above River Terraces
sea level.
River terraces are surfaces marking old
EROSIONAL LANDFORMS valley floor or floodplain levels. River
terraces are basically products of erosion as
Vallyes they result due to vertical erosion by the
stream into its own depositional floodplain.
Valleys start as small and narrow rills;
the rills will gradually develop into long and DEPOSITIONAL LANDFORMS
wide gullies; the gullies will further deepen,
widen and lengthen to give rise to valleys. Alluvial Fans
Depending upon dimensions and shape,
many types of valleys like V-shaped valley, Alluvial fans are formed when streams
gorge, canyon, etc. can be recognized. A flowing from higher levels break into foot
gorge is a deep valley with very steep to slope plains of low gradient. Alluvial fans in
straight sides and a canyon is characterized humid areas show normally low cones with
by steep step-like side slopes and may be as gentle slope from head to toe and they appear
deep as a gorge. A gorge is almost equal in as high cones with steep slope in arid and
width at its top as well as its bottom. In semi-arid climates.
contrast, a canyon is wider at its top than at
its bottom. In fact, a canyon is a variant of Deltas
gorge. Valley types depend upon the type
and structure of rocks in which they form. Deltas are like alluvial fans but develop
For example, canyons commonly form in at a different location. The load carried by
horizontal bedded sedimentary rocks and the rivers is dumped and spread into the sea.
gorges form in hard rocks. It this load is not carried away far into the
sea or distributed along the coast, it spreads
Potholes and Pluge Pools and accumulates as a low cone.

Over the rocky beds of hill-streams Floodplains, Natural Levees and Point Bars
more or less circular depressions called
potholes form because of stream erosion Floodplain is a major landform of river
deposition. The flood plains in a delta are
called delta plains.

Natural levees are found along the

Land Forms 101

banks of large rivers. They are low, linear islands of sand, gravel and pebbles develop
and parallel ridges of coarse deposits along on the floor of the channel and the water
the banks of rivers, quite often cut into flow is divided into multiple threads. These
individual mounds. During flooding as the thread-like streams of water rejoin and
water spills over the bank, the velocity of the subdivide repeatedly to give a typical braided
water comes down and large sized and high pattern.
specific gravity materials get dumped in the
immediate vicinity of the bank as ridges. They Groundwater
are nearer the banks and slope gently away
from the river. The levee deposits are coarser Here the interest is not on groundwater
than the deposits spread by flood waters as a resource. Our focus is on the work of
away from the river. When rivers shift groundwater in the erosion of landmasses
laterally, a series of natural levees can form. and evolution of landforms. The surface
water percolates well when the rocks are
Point bars are also known as meander permeable, thinly bedded and highly jointed
bars. They are found on the convex side of and cracked. After vertically going down to
meanders of large rivers and are sediments some depth, the water under the ground
deposited in a linear fashion by flowing flows horizontally through the bedding
waters along the bank. planes, joints or through the materials
themselves. It is this downward and
Meanders horizontal movement of water which causes
the rocks to erode. Physical or mechanical
In large flood and delta plains, rivers removal of materials by moving groundwater
rarely flow in straight courses. Loop-like is insignificant in developing landforms. That
channel patterns called meanders develop is why; the results of the work of
over flood and delta plains. groundwater cannot be seen in all types of
rocks. But in rocks like limestone or
As meanders grow into deep loops, the dolomites rich in calcium carbonate, the
same may get cut-off due to erosion at the surface water as well as groundwater
inflection points and are left as ox-bow lakes. through the chemical process of solution and
precipitation deposition develop varieties of
Braided Channels: When rivers carry landforms. These two processes of solution
coarse material, there can be selective and precipitation are active in limestone’s or
deposition of coarser materials causing dolomites occurring either exclusively or
formation of a central bar which diverts the inter-bedded with other rocks. Any
flow towards the banks; and this flow limestone or dolomite region showing typical
increases lateral erosion on the banks. As the landforms produced by the action of
valley widens, the water column is reduced groundwater through the processes of
and more and more materials get deposited solution and deposition is called Karst
as islands and lateral bars developing a topography after the typical topography
number of separate channels of water flow. developed in limestone rocks of Karst region
Deposition and lateral erosion of banks are in the Balkans adjacent to Adriatic sea.
essential for the formation of braided pattern.
Or, alternatively, when discharge is less and
load is more in the valley, channel bars and

102 Gist of NCERT (Geography)

The karst topography is also alternating beds of rocks (shales, sandstones,
characterized be erosional and depositional quartzite’s) with limestones or dolomites in
landforms. Indian subcontinent is full of between or in areas where limestone’s are
example of glaciers. It can be seen in dense, massive and occurring as thick beds,
mountainous area of Uttaranchal, Himachal cave formation is prominent.
Pradesh, Jammu Kashmir. The source of
Bhagirathi river is Gangotri glacier called Stalactites, Stalagmites and Pillars:
‘Gaumukh’. The source of Alakananda river Stalactites hang as icicles of different
is Alkapuri glacier. Where Alakhanda joins diameters. Normally they are broad at their
Bhagirathi at Devprayag it ows nomenclature bases and taper towards the free ends
as “The Ganga”. showing up in variety of forms. Stalagmites
rise up from the floor of the caves. In fact,
EROSIONAL LANDFORMS stalagmites form due to dripping water from
the surface or through the thin pipe, of the
Pools, Sinkholes, stalactite, immediately below it. Stalagmites
Lapies and Limestone Pavements may take the shape of a column, a disc, with
either a smooth, rounded bulging end or a
Small to medium sized round to sub- miniature crater like depression. The
rounded shallow depressions called swallow stalagmite and stalactites eventually fuse to
holes form on the surface of limestone’s give rise to columns and pillars of different
through solution. It might collapse leaving a diameters.
large hole opening into a cave or a void below
(collapse sinks). The term do line is Glaciers
sometimes used to refer the collapse sinks.
Solution sinks are more common than collapse Masses of ice moving as sheets over the
sinks. Quite often the surface run-off simply land (continental glacier or piedmont glacier
goes down swallow and sink holes and flow if a vast sheet of ice is spread over the plains
as underground streams and re-emerge at a at the foot of mountains) or as linear flows
distance downstream through a cave down the slopes of mountains in broad
opening. When sink holes and do-lines join trough-like valleys (mountain and valley
together because of slumping of materials glaciers) are called glaciers. The movement
along their margins or due to roof collapse of glaciers is slow unlike water flow. The
of caves, long, narrow to wide tranches movement could be a few centimeters to a
called valley sinks or Uvalas form. Gradually, few meters a day or even less or more.
most of the surface of the limestone is eaten Glaciers move basically because of the force
away by these pits and trenches, leaving it of gravity.
extremely irregular with a maze of points,
grooves and ridges or lapis. Especially, these We have many glaciers in our country
ridges or lapis form due to differential moving down the slopes and valleys in
solution activity along parallel to sub-parallel Himalayas. Higher reaches of Uttaranchal,
joints. The lapie field may eventually turn into Himachal Pradesh and Jammu and Kashmir,
somewhat smooth limestone pavements. are places to see some of them. River
Bhagirathi is basically fed by melt waters
Caves: In areas where there are from under the snout (Gaumukh) of the

Land Forms 103

Gangotri glacier. In fact, Alkapuri glacier glaciers cut head ward until their cirques
feeds waters to Alakananda river. Rivers meet, high, sharp pointed and steep sided
Alkananda and Bhagirathi join to make river peaks called horns form. The divides between
Ganga near Deoprayag. cirque side walls or head walls get narrow
because of progressive erosion and turn into
Erosion by glaciers is tremendous serrated or saw- toothed ridges sometimes
because of friction caused by sheer weight referred to as arêtes with very sharp crest
of the ice. The material plucked from the land and a zigzag outline.
by glaciers (usually large-sized angular
blocks and fragments) get dragged along the Glacial Valleys/Troughs
floors or sides of the valleys and cause great
damage through abrasion and plucking. Glaciated valleys are trough-like and U-
Glaciers can cause significant damage to even shaped with broad floors and relatively
un-weathered rocks and can reduce high smooth, and steep sides. The valleys may
mountains into low hills and plains. contain littered debris or debris shaped as
moraines with swampy appearance. There
As glaciers continue to move, debris may be lakes gouged out of rocky floor or
gets removed, divides get lowered and formed by debris within the valleys. There
eventually the slope is reduced to such an can be hanging valleys at an elevation on one
extent that glaciers will stop moving leaving or both sides of the main glacial valleys are
only a mass of low hills and vast outwash quite often truncated to give them an appear-
plains along with other depositional features. ance like triangular facets. Very deep glacial
The highest peak in the Alps, Matterhorn and troughs filled with sea water and making up
the highest peak in the Himalayas, Everest shorelines (in high latitudes) are called
are in fact horns formed through headword fjords/fiords.
erosion of radiating cirques.
Depositional Landforms
Erosional Landforms
The unasserted coarse and fine debris
Cirque: The cirques quite often are dropped by the melting glaciers is called
found at the heads of glacial valleys. The glacial till.
accumulated ice cuts these cirques while
moving down the mountain tops. They are Moraines: They are long ridges of de-
deep, long and wide troughs or basins with posits of glacial till. Terminal moraines are
very steep concave to vertically dropping long ridges of debris deposited at the end
high walls at its head as well as sides. A lake (toe) of the glaciers. Lateral moraines form
of water can be seen quite often within the along the sides parallel to the glacial valleys.
cirques after the glacier disappears. Such The moraine in the centre of the glacial val-
lakes are called cirque or tarn lakes. There ley flanked by lateral moraines is called me-
can be two or more cirques one leading into dial moraine.
another down below in a stepped sequence.
Eskers
Horns and Serrated Ridges
When glaciers melt in summer, the water
Horns form through head ward erosion flows on the surface of the ice or seeps down
of the cirque walls. It three or more radiating along the margins or even moves through
holes in the ice. These waters accumulate

104 Gist of NCERT (Geography)

beneath the glacier and flow like streams in are accomplished by waves. When waves
a channel beneath the ice. Such streams flow break, the water is thrown with great force
over the ground (not in a valley cut in the onto the shore, and simultaneously, there is
ground) with ice forming its banks. Very a great churning of sediments on the sea
coarse materials like boulders and blocks bottom. Constant impact of breaking waves
along with some minor fractions of rock drastically affects the coasts. Storm waves
debris carried into this stream settle in the and tsunami waves can cause far-reaching
valley of ice beneath the glacier and after the changes in a short period of time than normal
ice melts can be found as a sinuous ridge breaking waves. As wave environment
called esker. changes, the intensity of the force of breaking
waves changes.
Outwash Plains
Other than the action of waves, the
The plains at the foot of the glacial coastal landforms depend upon (i) the
mountains or beyond the limits of continental configuration of land and sea floor; (ii)
ice sheets are covered with glacio-fluvial whether the coast is advancing (emerging)
deposits in the form of broad flat alluvial fans seaward or retreating (submerging)
which may join to form outwash plains of landward. Assuming sea level to be constant,
gravel, silt, sand and clay. two types of coasts are considered to explain
the concept of coastal landforms: (i) high,
Drumlins rocky coasts (submerged coasts); (ii) low,
smooth and gently sloping sedimentary
Drumlins are smooth oval shaped ridge- coasts (emerged coasts).
like features composed mainly of glacial till
with some masses of gravel and sand. The High Rocky Coasts
long axes of drumlins are parallel to the
direction of ice movement. They may Along the high rocky coasts, the rivers
measure up to 1 km in length and 30 m or so appear to have been drowned with highly
in height. One end of the drumlins facing the irregular coastline. The coastline appears
glacier called the stoss end is blunter and highly indented with extension of water into
steeper than the other end called tail. The the land where glacial valleys (fjords) are
drumlins form due to dumping of rock debris present. The hill sides drop off sharply into
beneath heavily loaded ice through fissures the water. Shores do not show any
in the glacier. The stoss end gets blunted due depositional landforms initially. Erosion
to pushing by moving ice. Drumlins give an features dominate.
indication of glacier movement.
Along with rocky coasts, waves break
Waves and Currents with great force against the land shaping the
hill sides into cliffs. With constant pounding
Coastal processes are the most dynamic by waves, the cliffs recede leaving a wave-
and hence most destructive. cut platform in front of the sea cliff. Waves
gradually minimize the irregularities along
Some of the changes along the coast take the shore. The materials which fall off, and
place very fast. At one place, there can be removed from the sea cliffs, gradually break
erosion in one season and deposition in
another. Most of the changes along the coast