Lecture 13 & 14 : Geography

Topics Covered in this Lecture

  1. Glaciers :- Types and Movements
  2. Mechanisms of Glacial Erosion
  3. Glacial Erosional Landforms
  4. Glacial Depositional Landforms
  5. Mechanisms of wind erosion
  6. Aeolian Erosional Landforms
  7. Aeolian Depositional Landforms

Ice caps

When large blocs of ice cover the landform, it is known as icecap. Icecaps are found only in high latitudes in the form of sheets. There are 3 ice sheets in the world.

  1. Antarctic
  2. Iceland
  3. Greenland

Animals associated are seal, snow, leopard, polar bear, and penguins.

Note- the Karakoram is the heavily glaciated part of the world outside the polar regions.

Glaciers have very high erosive power and the major mechanism of erosion is Abrasion and Attrition.

The chief characteristics of the glaciated regions are that they are highly striated or scratched,

Erosional Landforms

Corrie/CWM

It is a horse shoe-shaped glacial trough having a steep wall and flat base.

Aretes

These are formed when two corries or glaciers cut down in opposite direction. They are used by mountaineers for climbing.

Pyramidal peak

Peaks in the glaciated region are sharp because corries cut down from all the sides, such peaks are pyramidal peaks. For example, mont blanc (Switzerland), the highest peak of Alps.

Berschgrund

These are at the head of the glacier, during the summer season the formed deep cracks. They are dangerous because they pose a maximum threat to mountaineers.

U-shaped valley

Glacier due to its erosional activity forms braoad and flat U-shaped valleys.

Hanging valleys

  • The tributary glaciers do not have the same erosional capacity as the main glaciers. Therefore, they erode the valleys of lesser depth as compared to the main glacier.

  • Thus, the tributary glaciers join the main glacier from a certain height. Such valleys are hanging valleys.

  • The hanging valleys are the natural sights of waterfalls and hence glaciated regions have high hydroelectricity potential.

  • The lakes in the regions of hanging valleys are Ribbon lakes. For example, in Arunachal Pradesh.

Depositional Landforms

Drumlimb

These are the group of oval, elongated hills having a whale back appearance. They are completely depositional landforms and since they occur in groups it is known as Basket of eggs topography.

Erratics

These are irregularly arranged rock which once represented the sites of glacier movement. After the melting of glaciers, irregular rocks were left stranded due to deposition.

Eskers

Long, narrow, meandering or sinuous ridges that are formed due to the melting of the glaciers and subsequent deposition are eskers. This represents the sites where the glaciers start melting and hence they are an example of fluvio-glacial-landforms.

Outwash Plains

These are formed entirely due to deposition. These are the sites where glaciers completely melt and form low hills known as Kames lakes in the depressions known kettle lakes. The entire topography if outwash plains are Knob and Kettle Topography.

Landforms having both erosional and depositional features

  1. Roche mountains– Both erosional and depositional feature found in the glaciated low land is known as Roche Mountains. The upstream side is gentle or comparatively smooth due to deposition of sediments while the downstream side is rough and steep due to plucking. It resembles skin of a SHEEP or covering commonly used in the equitorial regions of the world to protect from rainfall.

  2. Crag and tail topography– Crag is a mass of hard rock which is resistant to erosion. It obstructs the movement of glaciers and hence deposition starts over the period of time. After the melting away of ice, the entire topography develops in such a way that upstream side is comparatively gentle. This downstream side is tail.

Moraines and Tills

  • Moraines are glacial deposits which are made up of different rocks boulders, clay, and very fine material is till.

  • The glaciers scratches and breaks the side of a mountain to form lateral moraines.

  • When the two glaciers converge, the inside part of the lateral moraines join to form medial moraine. At the end of the glacier the transported material are deposited in a tongue-shaped manner to form terminal moraine.

  • As the glacier starts reducing at different stages, the terminal moraines start going backward and are known as Recessional Moraines.

Karst Topography

It occurs in the limestone rich regions. The topography found in the limestone rich regions which was first studied in erstwhile Yugoslavia.

Chief characteristics

  • Limestone is a very weak rock, especially when exposed to water. It is a well-jointed rock when exposed to water limestone reacts to form weak acid known as carbonic acid which will easily weather or erode the limestone rocks.

  • Water will enlarge the joints of limestone and hence the entire limestone pavement/rock will be converted into clints and grikes.

  • Grike is the joints that have been widened by either chemical weathering or river erosion while the flat pavements are clints.

  • It is a region of dry river valleys where the water flows underground.

  • The point from where the water has disappeared is sinkhole/swallow holes.

  • The sinkholes may join and enlarge to form Dolina. Several dolinas may merge to form Uvala. Sometimes due to rifting an extremely large depression is formed known as Rolje.

  • The limestone topography is dominated by numerous caves due to weathering and erosion of the limestone which is present inside the mountain.

  • Inside the cave, the most important features are stalactites, stalagmites, and pillars. Stalactites are sharp slender downward projections that grow from ceiling or roof.

  • Stalagmites on the other hand are rounded short projections growing from the ground.

  • Stalactites and stalagmites may join to form limestone pillars.

  • These features are formed when calcium carbonate remains but water evaporates.

The famous are:

  1. Batu caves (Malaysia)
  2. Kentucky caves (USA)
  3. Cockpit country (Jamaica)
  4. Garo Hills (Meghalaya)

Topics Covered in this Lecture

  1. Mechanisms of Coastal Landforms
  2. Coastal Erosional landforms
  3. Coastal Depositional Landforms
  4. Conditions for the development of karst landforms
  5. Erosional Features
  6. Depositional Features

Desert Landform

There are 4 types of desert:

  1. Hamada or Rocky desert- For example, Leh Laddakh region.
  2. Reg or stony desert
  3. Erg or Sandy desert
  4. Bajada- These are formed when there’s an action of water in the areas of deserts.

    Water in the deserts regions causes soil erosion resulting into formation of bad land topography consisting of gullies and ravines. This is known as Bajada.

The most important mechanism in the deserts are abrasion (when sand particles hit the rocks and thus, eroding them.

Sand is an effective agent of erosion only at lower height- i.e., 180 cm from ground.

Attrition- Sand particles rub against themselves and becomes fine.

Deflation- It is the Process by which wind lifts the sand particles. The lifting of sand particles by the wind results in the formation of deflation hollows.
The deflation hollows result in the formation of Oasis. For example, Qattara depression- a famous oasis in Egypt- 133 m deep.

Erosional landform

Mushroom rocks or gaur or Rock Pedestal

Sand blasting (abrasion) is effective only up to a lower height. As the wind doesn’t have any direction, it will erode the base of rock from all the sides. Such rocks are mushroom rocks or Gaur or Pedestal.

Yardang

  • Such a topography occurs when there is an alternate arrangement of hard and soft rock in vertical banks.

  • Differential erosion of hard and soft rocks results into the formation of ridge and furrow landscape.

  • The region of a soft rock becomes the lines of communication in the densest regions.

Zuegens

This occurs when mass of hard and soft rocks are arranged in alternate banks but in horizontal manner. The hard rock is more resistant to erosion but the soft rocks are easily eroded. Hence, such topography is known as ink pot topography.

Mesa and Buttes

These are formed due to differential erosion of hard and soft rocks. The layer of hard rock at the top protects the lower soft rock from erosion while the soft rock in the other region is exposed to wind causing sand blasting and greater erosion.

As a result flat mountains have a steep sides are formed. Bigger mountains known as Mesas and smaller mountains are Buttes. These are found in the semi arid regions of Deccan lava plateau.

Inselberg

An isolated residual hill which is made up of hard rock such as gneiss having rounded top are known as inselbergs. It represents the final stage or the old age in the cycle of erosion where the entire land is flat except the hard granitic or gneiss rock. For example, Aravalis.

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