Landform And Their Evolution Class 11 Notes Geography Chapter 6 - CBSE
Chapter : 6
What Are Landform And Their Evolution ?
"उत्तर पुस्तिकाओं का मूल्यांकन करते समय यह पाया गया कि विद्यार्थी प्रायः अपठित गद्यांश को ध्यानपूर्वक नहीं पढ़ते और उसका मूल भाव ग्रहण न कर पाने के कारण प्रश्नों के उत्तरों में त्रुटियाँ कर देते हैं।"
- Landforms are small-to-medium tracts or parcels of the earth’s surface having their own physical shape, size, and materials and are the result of the action of certain geomorphic processes and agents. Several related lanforms together make up large tracts of earth’s surface known as landscapes.
- Running water, groundwater, wind, glaciers, waves, and currents are the most significant geomorphic agents working on the earth materials and causing changes on its surface through weathering processes and erosion.
- Evolution involves the stages of transformation of the earth’s surface from one landform into another or of individual landforms after their formation. Each and every landform has a history of development which changes with time passing through stages of development.
Running Water
Running water is the most important geomorphic agent in causing the degradation of land surface. Most of the erosional landforms are associated with vigorous and youthful rivers flowing over steep gradients. With time, stream channels over steep gradients turn gentler due to continued erosion and lose their velocity facilitating active deposition and forming depositional forms associated with streams flowing over steep slopes. The friction of the column of flowing water removes the materials from the surface to the direction of flow, forming small and narrow rills and developing into long and wide gullies which further deepen, widen, lengthen, and unite to give rise to a network of valleys.
Erosional Landforms
Erosional Landform by running water are valley, Potholes, Plunge pool, Incised or Entrenched Meanders, River Terraces, etc.
Deposition Landforms
Desposition Landform by running water are Alluvial Fans, Deltas, Meanders, Floodplains, Natural Levees, and Point Bars.
Groundwater
The work of groundwater in the erosion of landmasses and evolution of landforms starts with the surface water percolating through the permeable, thinly-bedded, highly-jointed, and cracked rocks. The water under the ground flows horizontally through the planes, joints, or the materials themselves which causes the rocks to erode. The result is seen in rocks rich in calcium carbonate, such as limestones or dolomites, where the surface as well as groundwater develop varieties of landforms through the chemical process of solution and
precipitation deposition, also referred to as ‘Karst topography’.
Erosional Landforms
Erosional Landform by groundwater are Pools, Sinkholes, Lapies, Limestone Pavements, and Caves.
Deposition Landforms
Desposition Landform by groundwater are Stalactites, Stalagmites, and Pillars.
Glaciers
Glaciers are masses of ice moving as sheets over the land or as linear flows down the slopes of mountains in broad trough-like valleys which move slowly due to the force of gravity but causes tremendous erosion by the friction caused by the weight of ice. The material plucked from the land get dragged along the floors or sides of the valleys causing great damage to un-weathered rocks and reduce high mountains into low hills and plains through abrasion and plucking.
Erosional Landforms
Erosional Landform by Glaciers are Cirque, Horns, Serrated Ridges, Glacial Valleys/Troughs.
Deposition Landforms
Desposition Landform by Glaciers are Moraines, Eskers, Outwash Plains, Drumlins.
Waves And Currents
Coastal processes are the most dynamic and the most destructive. Most of the changes along the coasts are accomplished by waves. When waves break, the water is thrown with great force onto the shore, and there is a simultaneous, great churning of sediments on the sea bottom. Constant impact of breaking waves drastically affects the coasts. The coastal landforms depend upon the action of waves, the configuration of land and sea floor, and whether the coast is advancing (emerging) seaward or retreating (submerging) landward. Assuming sea level to be constant, two types of coasts explain the concept of evolution of coastal landforms, i.e., High Rocky Coasts and Low Sedimentary Coasts.
Erosional Landforms
Erosional Landforms due to waves and currents are Cliffs, Terrace, Caves, and Stacks.
Deposition Landforms
Desposition Landforms due to waves and currents are Beaches, Dunes, Bars, Barriers, and Spits.
Winds
Wind is the most dominant agent in hot deserts. Winds move along the desert floors with great speed and the obstructions in their path create turbulence which are very destructive. These cause deflation by lifting and removal of dust and smaller particles from the surface of rocks, abrasion through transportation of sand and silt as effective tools to abrade the land surface, and impact by the sheer force of momentum. The wind action creates numerous erosional and depositional features in the deserts.
Erosional Landforms
Erosional Landforms by winds are Pediments, Pediplains, Playas, Deflation Hollows, Caves, Mushroom Rocks, Table, and Pedestal Rocks.
Deposition Landforms
- Wind is a good sorting agent; depending upon the velocity of wind, sizes of grains, and the process of transportation, depositional landforms are formed.
- Sand Dunes: There are a variety of dunes including the crescent-shaped barchans, the partially vegetated parabolic dunes, the one-winged seifs, the longitudinal dunes with poor sand supply and constant wind direction, and the perpendicularly aligned transverse dunes.
