Rajasthan Board RBSE Class 11 Geography Notes Chapter 10 Agents of Erosion
→ Internal and external forces create various topographies on the earth’s surface.
→ External forces perform the work of denudation of rocks by the activities of weathering, erosion and mass translocation.
→ Erosion is a dynamic process. Forces such as rivers, oceanic waves, winds, glaciers and underground water which participate in erosion are known as the factors of erosion.
→ Climate, situation, structure and composition of rocks are the factors which affect erosion.
→ Erosive and depositional activities play an important role in the formation of various topographies on the surface of the earth.
→ Activities of erosion and deposition are mainly visible in the form of river or fluvial topographies, oceanic waves or coastal topographies, wind or arid topographies, glaciers or glacial topographies and underground water or Karst topographies.
- Due to increasing water, erosion takes place in the background, and in the bottom and deposition of the eroded debris also takes place. Two types of topographies are formed due to this: erosional topography and depositional topography.
- Gorges, canyons, waterfalls, rapids, potholes, structural terrace, river meanders and peneplanes are among the major topographies which are formed by erosion.
- Alluvial cones, alluvial fan, delta, natural levees, flood plains and oxbow-lakes are the major among depositional topographies.
Sea Waves-Coastal Topographies
- Ripples which emerge upon the surface of the sea due to the blowing of winds are known as waves.
- Waves perform the activities of hydrolysis, corrasion, attrition and hydraulic pressure due to which, erosional topographies are formed through erosion and depositional topographies are formed through the deposit of debris.
- Cliffs, caves, sea caves, blowouts, natural arch, stacks, wave cot platforms, etc. are included in erosional topographies.
- Beaches, cusp beaches, spits, bars, offshore bars, hooks, loops, connecting bars, lagoons and bay bars and tumbolo, etc. are included in depositional topographies.
- Topographies which are formed in desert regions due to the result of blowing of winds are known as wind-born or arid topographies.
- Winds perform transportation, corrasion, attrition in desert regions and cut, erode and transport the rock particles of rocks and perform their deposition at other places.
- Two types of topographies are formed through winds in desert regions: erosional topographies and depositional topographies.
- Blow outs, inselberge, mushroom rocks, demoiselles, driekanter, stone lattice, zeugen/zeujen, yardang, etc. are included in erosional topographies.
- Sand dunes, ripples, sand drifts, sand levees and loess are included in depositional topographies.
- Glaciers gradually shift from their place of agglomeration on the surface.
- In glaciated regions, glaciers perform weathering of rocks through plucking, repulsion and attrition and deposit the moraines in various forms.
- Various erosional and depositional topographies are formed in glacial regions.
- U-shaped valleys, hanging valleys, glacial tarns, nunataks, cols, crags and tails, sheep rocks and fjord are included in erosional topographies.
- Moraines, eskers, kames, kettles, drumlins and glacial precipitant valleys are included in depositional topographies.
- Water situated in holes and cracks of underground rocks present below the earth’s surface is known as groundwater.
- In regions of limestone rocks, groundwater forms various landforms above and below the surface of groundwater through the process of oxidation.
- Region of lime is known as karst region. The term ‘karst region’ has originated from the Yugoslavian word ‘krass region’. On the basis of this name, topographies formed in limestone regions in all the countries of the world are known as karst topographies.
- Two types of topographies are present in lime regions: erosional topographies and depositional topographies.
- Tera-Rossa, lapies, sink-holes, swallow holes, dolines, uvalas, polijes, sinking creeks and blind valleys are included in erosional topographies.
- Stalactites, stalagmites, cave pillars, dripstones and nodules are included in depositional topographies.
Agents of Erosion Notes Important Terms
→ Denudation: Depletion of layers of rocks or land erosion caused by physical factors, which includes weathering, erosion and mass translocation.
→ Fluvial Topographies: Flowing water rakes and scrapes the background of the water valley, separates the rocky material, transports it along and deposits it at another place. Topographies which are formed through this process are known as fluvial topographies.
→ Coastal Topographies: Topographies which are formed by erosion and deposition caused by sea waves are known as coastal or tidal waves-born topographies.
→ Arid Topographies: The erosional and depositional activities caused by blowing winds in arid regions form various topographies. Such topographies are known as arid or wind-born topographies.
→ Glaciated Topographies: In glaciated regions, glaciers perform erosion of rocks by evulsion, corrasion and attrition and deposit the moraines in various forms due to which various erosional and depositional topographies are formed in glaciated regions. Such topographies are known as glaciated or glacial topographies.
→ Karst Topographies: In limestone regions, underground water forms various types of topographies above and below its surface through the process of oxidation. Lime topographies are known as karst topographies.
→ Estuary: The submerged mouth of the river, where conjunction of water coming from surface and saline water takes place, is known as estuary.
→ Gorge: A narrow valley between hills or mountains, typically with steep rocky walls and a stream running through it.
→ Canyon: Canyon is a comparatively narrower and deeper valley than a gorge which has edges with vertical slope.
→ River Meanders: These are excessively circuitous turns of the river, where the river flows like a snake.
→ Peneplain: Shapeless lowland plain formed in an arid climate region during the final stage of the erosion cycle in which residue of solid rocks are exceptionally found here and there in the form of dunes.
→ Alluvial Cone: This refers to the deposit of debris in the shape of cone on the mountainous slope as the river enters into the plains from the mountains.
→ Natural Levees: These are walls of sandy soil formed on both sides of the river due to less water level.
→ Attrition: The process of mutual friction and breaking down of rock particles or rock segments flowing along with wind, water and glaciers, due to which the size of rock particles becomes smaller than before.
→ Sea Caves: Due to continuous erosion of gorges formed by waves in coastal regions, oceanic caves are formed. These are also known as oceanic caves.
→ Blow-out: Tidal waves form holes on the ceilings of coastal caves which are known as blow-outs.
→ Stack/Cave pillar: Pillar which is formed due to the breaking down of the ceiling of a natural arch is known as cave pillar or stack.
→ Wave Cat Platform: This is just like platforms built due to the cliff continuously shifting backward. Due to this, platform or leveled plain with gradual slope and bare rocks is formed in the sea in front of the cave. It is known as wave cat platform or plain.
→ Beach: Beaches are formed due to deposit rocks debris by the waves on the edges of the seashore.
→ Cusp Beach: Triangular beach formed from pebbles, stones, boulders, etc. which extends vertically towards the sea is known as cusp beach.
→ Spit: Deposit made by waves in the form of tongue towards the sea is known as spit. It is formed from the material deposited by offshore flow which takes the form of offshore bars.
→ Bars: Ridges or dams formed from deposition performed by waves are known as bars. This is parallel to the shore and usually at the time of high tide, oceanic water crosses the bar and reaches the shore.
→ Connecting Bars: Dam, ridge or wall which joins two islands are known as connectors or connecting bars.
→ Tumbolo: Bars which connect the islands with the shore are known as tumbolos.
→ Blow out: Those troughs which are formed by loose and disorganized terrain or rock parts blown and carried away by the wind are known as blowouts.
→ Inselberge: These are projected dunes of solid rocks in the desert-like large seas, and they appear to be like an island or a mountain.
→ Demoisells: Those surface columns in deserts which are protected with cover of solid rocks or terrain are known as demoisells.
→ Driekanter: A Dreikanter is a type of ventifact that typically forms in desert or periglacial environments due to the abrasive action of blowing wind.
→ Stone Lattice: This is a reticulated rock which is formed by the process of corrasion by the wind upon rocks with different compositions.
→ Zeugen: These are holes formed by erosion of wind in the layers of solid and gentle rocks spread alternately in horizontal form.
→ Yardang: These are pointed earth-shaped structures formed by respective vertical layers of hard and soft rocks.
→ Ripples: These are landforms which emerge on sandy surface of the desert just like oceanic waves.
→ Sand Drift: These are vertically moving guilds of sand, situated on the edge of topographical obstruction.
→ Sand Levees: These are vertical guilds of sand with a broad peak.
→ Loess: Deposit of very fine dust particles brought by blowing wind is known as loess. Their deposition takes place in places far away from deserts. Loess is usually yellow in colour.
→ Tarn: This is a lake formed by water getting filled up in cirque basin. Due to erosion of glacial valley, a small trough is formed at the bottom of the cirque basin. When the glacier melts, this trough gets filled up with water. This is generally known as tarn.
→ Nunatak: Projected dunes situated in glacial regions are known as nunatak. This is like an island in the middle of glacial cover. Nunatak usually develops in Antarctica continent and Greenland.
→ Gol: This is a traverse path formed by the conjunction of two adjacent cirques. Winds blow in different directions on the edges of the col and anti-synclines and depression, but winds are slow and discrete in the inner part of col.
→ Crag and Tail: A rocky outcrop with a tapering ridge of glacial deposits extending to one side.
→ Sheep Rock: This is a glacial rock or stone which resembles the shape of the back of sheep. Its slope which is in front of the glacier is gradual and its slope on the back is steep. These are also known as sheep-back shaped rocks.
→ Fjord: These are eroded coasts formed by submergence of glacial valleys. This is a landform which is deep, long, narrow and has steep slope.
→ Moraines: Deposits of pebbles, stones and boulders deposited by glaciers. These are situated on the edges, back and bottom of the glacier.
→ Esker: These are long, narrow and wavy ridges or dams formed by the deposit of glacial alluvium.
→ Kame: These are dunes which have steep slopes and are formed by glacial alluvium. They are formed by deposit of sand and gravel on abjection plains formed by glaciers.
→ Kettle: These are troughs which are formed by the melting of glaciers. These are small troughs formed in glacial plains.
→ Drumlin: Egg-basket shaped structure formed from the deposition of boulder bodies. Axis of drumlin is parallel to the direction of flow of the glacier. Drumlins are found on a large land part of Northern Ireland, Northern England and Northern United States of America.
→ Tera-Rossa: Red and brown soils formed by the process of oxidation are known as Tera-Rossa.
→ Lapies: These are pointed and thorny topographies which resemble lake beds.
→ Sink-Hole: These are troughs formed by the process of oxidation of water containing carbon dioxide. Swallow holes and dolines are also the same type of troughs, but they are comparatively larger in size.
→ Swallow-Hole: These holes are bigger in size as compared to sink holes.
→ Doline: Holes that are bigger in size or shape are known as dolines. Dolines usually originate due to expansion of swallow holes.
→ Uvala: These are expansive troughs formed by the mutual conjunction of various dolines. Uvalas usually have steep slopes and deposit of alluvium is found at their bottom.
→ Polije: These are expansive and larger-sized troughs formed by the conjunction of many uvalas. They are more extended than dolines and their walls are usually vertical.
→ Sinking Creek: Innumerable holes or pores on the edge of lime, from where water appears to be sinking are known as sinking creeks.
→ Stalagmite: This is a pillar-shaped structure formed on the ground of the cave. It is formed by the water dripping on the ground. Height of these pillars continues to increase due to progressive deposition.
→ Cave Pillar: This is a pillar-shaped structure formed by the conjunction of stalactite and stalagmite.
→ Drip-Stone: This is a lime pillar which resembles a curtain. It is situated at the bottom of the cave.
→ Nodules: Deposit of a type of mineral oil derived from rock holes is known as nodules.