GEOGRAPHY�CLASS-11�CHAPTER- LANDFORMS AND THEIR EVOLUTION

PRESENTED BY

ARUN KUMAR SHARMA

PGT-GEOGRAPHY

JNV MANSA

Introduction

• After weathering, geomorphic agents operate the landforms to change.
• Landform: small to medium reacts or parcels of the earth’s surface are called landforms.
• Several landforms together are called landscape Each landform has its own shape, size and materials Geomorphological processes are slow but significant in long run Every landform has a beginning, they change their shape and composition in course of time.
• Due to changes in climate and vertical and horizontal movements landforms change their shape.

RUNNING WATER

• Fluvial landforms are those landforms which are shaped and modified by the running water. Running water has sculpted most of the land surface across the world in comparison to other agents of erosion like wind or Glacier.
• Streams are in a constant process of shaping the land surface into newer forms.
• The running water erodes even the loftiest of mountains and carves deep valleys or gorges into it.
• Besides erosion it transports heavy load from one place to the other.
• The present chapter focuses on the landforms produced by fluvial processes. This encompasses both the erosional and depositional landforms produced by the running water.

Types of Running Water

• In the early stages, down-cutting dominates during which irregularities such as waterfalls and cascades will be removed.
• In the middle stages, streams cut their beds slower, and lateral erosion of valley sides becomes severe.
• The divides between drainage basins are likewise lowered until they are almost completely flattened leaving finally, a lowland of faint relief with some low resistant remnants called monadnocks standing out here and there.
• This type of plain forming as a result of stream erosion is called a peneplain (an almost plain). The characteristics of each of the stages of landscapes developing in running waterregimes may be summarised as follows:

Youth Stage

• Streams are few during this stage with poor integration and flow over original slopes showing shallow V-shaped valleys with no floodplains or with very narrow floodplains along trunk streams.
• Landforms of Youth Stage

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Mature Stage

• During this stage streams are plenty with good integration. The valleys are still V-shaped but deep; trunk streams are broad enough to have wider floodplains within which streams may flow in meanders confined within the valley. The flat and broad inter stream areas and swamps and marshes of youth disappear and the stream divides turn sharp. Waterfalls and rapids disappear

Old Stage

• Smaller tributaries during old age are few with gentle gradients. Streams meander freely over vast floodplains showing natural levees, oxbow lakes, etc. Divides are broad and flat with lakes, swamps and marshes. Most of the landscape is at or slightly above sea level.

EROSIONAL LANDFORMS

• Erosion is a process in which the surface of the earth is worn away by various agents of erosion like wind, water or Glacier. The removed material is carried away and deposited elsewhere. Erosion by streams occurs through several processes going together. These processes are Abrasion, Hydraulic action, Solution and Attrition.

• Abrasion: Running water when armed with sand, silt and other sediments acts as very effective means of erosion of the river bed.
• Solution: Pure water seldom exists in natural conditions. It contains various gases and acids in them, the water is charged with the acids and act as an important solvent.
• Attrition: When the stream loads (pebbles, sand, silt etc) move together, they cause their own wear and tear by colliding with one another. This rounding and shaping of these pebbles and boulders amongst themselves is called attrition.

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Erosional Landforms

• V shaped valley: Deep cutting and erosion by rapid flow of the stream carves out a valley that resembles the English letter V. The V shaped valley has a deep and narrow bottom (or valley) floor with steep valley sides.

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Gorge

• It is a narrow chasm with a very steep precipitous wall. These are common features found very often in mountainous regions. The Himalayas are home to a number of gorges located at different places in its ranges. The Kali Gandaki Gorge is one of the deepest gorges in the world.

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Gorge

Waterfalls

• It refers to a sudden descend of the flow of the stream or river caused by a variety of factors. They are very picturesque and beautiful features. Waterfalls may result due to variation in the resistance of rocks, crust deformation, changes in the sea level etc. Niagara Fall is a perfect example of

Niagara Fall

Potholes and Plunge Pools

• Potholes -Over the rocky beds of hill-streams more or less circular depressions called potholes form because of stream erosion aided by the abrasion of rock fragments.
• Plunge pools: large and deep holes at the base of waterfalls are called plunge pools.

DEPOSITIONAL LANDFORMS

• When a stream carrying heavy load descends from a narrow mountain valley onto a plain, it leaves behind its load in the form of a fan or a cone. This deposit at the base of a mountain occurs due to sudden drop in the velocity of the stream which cannot carry further such a heavy load on a plain region as it lacks gradient that earlier provided velocity to the stream enabling it to carry enormous load with much ease.

Fan on River Kosi at the base of the Himalyas

Floodplains

• Floodplain is a very gently sloping flat region bordering the stream. It is covered with fine silt, mud sand etc. brought down by the river and deposited in the adjoining region due to its regular flooding.

Natural Levees and Point Bars

• Natural levees and point bars are some of the important landforms found associated with floodplains. Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges of coarse deposits along the banks of rivers, quite often cut into individual mounds. Point bars are also known as meander bars.

Meanders

• stream flowing on a flat or a gently sloping surface seldom flows straight;
• it tends to take a sinuous course. While flowing it makes gentle loops in its flows commonly referred to as meander.
• The abandoned meander loops form ox bow lakes in the flood plains.

Meanders

Meanders and Ox-Bow Lake

RIVER DELTA

Deltas are like alluvial fans but develop at a different location. The load carried by the rivers is dumped and spread into the sea.

Mississippi Delta

The Karst Landforms

• Karst is a landscape which is underlain by limestone and has been eroded by dissolution, producing towers, fissures, sinkholes, etc. It is so named after a province of earlier
• Yugoslavia on the Adriatic sea coast where such formations are most noticeable.
• The development of all karst landforms requires the presence of rocks such as limestone, dolomite, and gypsum which is capable of being dissolved by surface water or groundwater.

Conditions essential for development of Karst Topography

• 1. Presence of soluble rocks, preferably limestone at the surface or sub-surface level.
• 2. These rocks should be dense, highly jointed and thinly bedded.
• 3. Presence of entrenched valleys below the uplands underlain by soluble and well- jointed
• rocks. This favours the ready downward movement of groundwater through the rocks.
• 4. The rainfall should be neither too high nor too low.
• 5. There should be a perennial source of water.

Erosional Landforms

• Karren/Lapies: Karrens are highly corrugated and rough surface of limestone lithology with low ridges and pinnacles.
• These are formed when rain falls onto bare limestone or waves break into it.
• Therefore, falling droplets, sheet and channelled runoff, film flow and ponded water all create small scale solution forms also termed as lapies.

Terra Rosa

• These are red clay stones up to several meters thick and kilo-metres across that occur at the earth’s surface. These are thought to be formed by residual dissolution of limestones and/or by accumulation of detrial mud, ash or dust on pre-existing karst terrain.

• Cavern: This is an underground cave formed by water action by various methods in a limestone or chalk area. There are differing views on the mode of formation of these caverns
• Arch/Natural Bridge: These are formed due to collapse of the roofs of caves or due to disappearance of surface streams and their reappearance; which keeps standing forming an arch.
• Sink Hole/Swallow Hole:
• Sink holes are funnel-shaped depressions having an average depth of three to nine metres and, in area, may vary from one square metre to more. These holes are developed by enlargement of the cracks found in such rocks, as a result of continuous solvent action of the rainwater.

• Dolines: Dolines are bowl shaped enclosed depressions in the Karst terrain that can be several metres to several hundred metres in range.
• Uvala-
• A number of adjoining dolines may come together to form a large depression called uvala.
• Polje-
• A number of uvalas may coalesce to create a valley called polje which is actually a flat-floored depression. An ideal polje is an elongated, flat-floored, closed depression surrounded by limestone hills that are well karstified.

Depositional Landforms

• Stalactites, Stalagmites and Pillars
• Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms.
• Stalagmites-
• Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it.
• The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.

GLACIERS

• Glaciers and ice sheets are the world’s main storehouse of fresh water. They are the thick and large masses of slow moving ice under the influence of gravity. They are formed by compression of snow. The mass of ice is mostly confined in the areas where the temperature is below zero degrees Celsius. They are found in the high latitudes or high altitudes. In higher latitudes, glaciers are seen even on the flat ground. In low latitudes, the glaciers are found in the higher altitudes.

EROSIONAL LANDFORMS

• Cirque:The shape of the cirque is just like an armchair and it is being made by glacial erosion.
• When the glacier descends from the mountain slope, it moves faster due to very steep slope.
• Later when the slope lowers, the excessive accumulation of ice exerts enormous pressure and the base is eroded by ice rotation, plucking and abrasion.

Aretes:

When several cirques or corries are developed on different sides of a mountain peak,

their separating boundaries are further narrowed and sharpened. The sharp knife or blade edged boundaries are called arêtes.

Horn or Pyramidal Peak: When the glaciers are developed from different sides of a peak, they erode the preexisting surface of the peak successively and make it a sharp and pointed peak with very steep slope. This gives a rise of a pyramidal peak which is also termed as horn as it is very pointed

Hanging Valley:

Hanging valley is a tributary glacial valley of a main glacier. Main glacier has huge amount of ice, hence, erode the base greater. Therefore, the main glacial valley is much deeper.

Depositional Landforms

Moraine:

• The materials carried by the glacial ice is deposited in an ideal condition when the carrying capacity is reduced. These deposits are generally unsorted and un-stratified as it is deposited as and when the material reaches and dropped.

Esker:

• Esker is a long, narrow and zigzag ridge like structure generally made up of stratified sediments deposited by subglacial meltwater .Its height varies from 5 meter to 50 meter and width is 50 meter to 500 meter whereas the length many as 500 meter to many kilometers.

Drumlins

• Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement.

COASTAL PROCESSES AND LANDFORMS

• The landscape is sculptured by the various processes operating on the surface of the earth. Mass wasting, erosion by wind, rivers, underground water, glaciers all contribute to shape and modify the landscape. In this Chapter we understand the coastal processes that are shaping the landscape and see how the waves through the process of erosion, transportation and deposition of detrital material continues to bring changes in the shorelines of the earth. Waves transfer the energy they derive from wind to shoreline that in turn is used to erode, move sediments and deposit them forming various coastal features.

Waves

• Waves are undulations over water surface resulting due to action of wind. As the wind blows over water, it produces stress and pressure variations on the surface, resulting in generation of waves that grow as result of pressure contrast between their driven (upwind) and advancing (downwind) slopes.
• The water then retreats back due to gravity and drains back towards the sea as backwash. In this process the water transports some of the sand from the beach back in sea. The process continues and with each swash and backwash sand material is continuously being flung on shore and then returning back to sea.

Erosional Coastal Landforms

• Cliff -The seaward limit of coast in some places is marked by a nick or scarp commonly known as cliff.

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• Caves-As the cliff recedes coastal erosional processes of weathering and erosion penetrate zone of weakness such as faults, joints or outcrops of less resistant rocks.

• Stacks-Dissection of headlands on a cliffed coast often isolate stacks either when a natural arch collapses or when a transverse inlet is cut along a zone of weakness through the headland.

DEPOSITIONAL LANDFORMS

• Beaches-Beach is an accumulation of loose unconsolidated sediment, temporary veneer of rock debris ranging in size from very fine sand, to pebbles, cobbles and occasionally boulders. Nearly about 40 percent of the coastline of the world consist of unconsolidated deposits of sand and gravel.
• Spits-The spits are beaches that are built above high tide level, diverging from the coast, ending in one or more landward hooks or recurves . The outlines of the spits are shaped by the dominant pattern of wave action, and they grow in direction of longshore drift by waves arriving at an oblique angle to the shore

Bar & Barrier Bar

• A ridge of sand and shingle formed in the sea in the off-shore zone (from the position of low tide waterline to seaward) lying approximately parallel to the coast is called an off-shore bar. An off-shore bar which is exposed due to further addition of sand is termed a barrier bar.

Wind

• Wind erodes, transports and deposits smaller particles like sand but may move even larger particles under special conditions. These processes lead to a variety of features. The scale of features ranges from very small to a vast expanse of several thousand square kilometers.

Erosional Land features

Pediments and Pediplains-

Landscape evolution in deserts is primarily concerned with the formation and extension of pediments. Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris, are called pediments.

�hollow�

• As the name suggests, these are low-lying surfaces which have been cleared of all loose particles and converted into hollows. The size of these depressions may range from a few metres in diameters and depth, to several kilometers.
• Yardang -
• These are parallel ridges separated by parallel ‘u’-shaped grooves, both developed in the direction of dominating wind flow in the region.
• Zuegen- These are similar to yardang, except they are smaller in scale and grooving is related to softer material alternated with more resistant rock beds.

Mushroom Rock- The base of a rock projection is eroded while the top is untouched by wind action, or is protected by some harder rock. Weak rock beds are eroded while harder beds stand out

Depositional Land features

• Sand dunes- Sand dunes are defined as hills and mounds of sand. They have a large variety and are classified on different bases.
• Barchan – Barchans are crescent shaped dunes. They are either single or may form groups. They migrate in the downwind direction, but maintain their shape as they move.
• Parabolic dunes form when sandy surfaces are partially covered with vegetation. That means parabolic dunesare reversed barchans with wind direction being the same.
• Seif is similar to barchan with a small difference. Seif has only one wing or point.