Landforms Part-II

• 17 May 2022

What is the Landform Made by Wind?

• Wind is a geomorphic agent in all terrestrial environments. It is more active in arid regions with fine-textured soils and sediments and little or no vegetation.
• Wind can erode desert rocks in two ways:
  • Deflation: The removal of fine, loose particles from the surface of rocks.
  • Abrasion: Small particles being carried by the wind scrape of particles from the rock surface. It then transports the eroded material by three processes:
    • Suspension: Very small particles (<0.15mm) are picked up and carried by the wind.
    • Saltation: Small particles (0.15-0.25mm) are temporarily lifted from the ground and bounce along the surface.
    • Surface Creep: Larger particles (>0.25mm) are hit and pushed along the ground by particles being moved by saltation.
  • Attrition:
    • Sand particles carried by winds start a friction process within itself and because of this their size reduces. This is known as attrition.
    • Erosion process of high speed winds is also fast.
    • Soft rocks break down easily but on the other hand the erosion process is long in case of hard rocks.

Erosional Landforms formed by Wind

• Deflation Hollows and Caves:
  • Deflation Hollows:
    • Deflation basins, called blowouts, are hollows formed by the removal of particles by wind.
    • Blowouts are generally small, but may be up to several kilometers in diameter.
  • Caves:
    • As wind-borne sand impacts the rock faces, some of the blow-outs become deeper and wider and fit to be called caves.
• Yardangs:
  • Yardangs are parallel troughs cut into softer rock running in the direction of the wind, separated by ridges. The direction of the yardangs can indicate the direction of the prevailing wind. 
• Zeugen:
  • A zeugen is a tabular mass of resistant rock, standing prominently in the desert.
  • It is usually composed of alternating layers of hard and soft rocks.
• Playas:
  • Playa is a flat-bottom depression found in interior desert basins and adjacent to coasts in arid and semiarid regions, periodically covered by water.
  • It slowly filtrates into the groundwater system or evaporates into the atmosphere, causing salt, sand, and mud deposition along the bottom and around the depression's edges.

Depositional Landforms formed by Wind

• Ripples:
  • They are regular, wavelike undulations lying at right-angles to the prevailing wind direction.
• Loess:
  • Loess is terrestrial sediment composed largely of windblown silt particles made of quartz. Loess requires three things:
    • A source of silt
    • Wind to transport the silt
    • A suitable site for deposition and accumulation
• Dunes:
  • Dunes are collections of loose sand built piecemeal by the wind.
  • It is usually composed of quartz, which is extremely hard and doesn’t easily decay.
  • Most Common types of Dunes:
    • Barchans:
      • Barchans have crescent-shaped points or wings that face away from the wind, or downwind, and where sand is moving over an almost uniform surface from where the wind is constant.
    • Seif:
      • It is also called linear dunesis similar to barchans with a small difference as it has only one wing or point.

What are the Coastal Landforms?

• Coastal processes are among the most dynamic geologic processes since changes in the morphology of many coasts can be seen on an annual (or shorter) timescale.
• Other than the action of waves, the coastal landforms depend upon:
  • The configuration of land and sea floor
  • Whether the coast is advancing (emerging) seaward or retreating (submerging) landward.

Erosional Coastal Landforms

• Cliffs, Terraces, Caves and Stacks:
  • Cliffs:
    • A sea cliff is a vertical precipice created by waves crashing directly on a steeply inclined slope. Hydraulic action, abrasion, and chemical solution all work to cut a notch at the high water level near the base of the cliff. Constant undercutting and erosion causes the cliffs to retreat landward.
  • Sea Caves:
    • Sea caves form along lines of weakness in cohesive but well-jointed bedrock. Sea caves are prominent headlands where wave refraction attacks the shore.
  • Sea Stacks:
    • A sea arch forms when sea caves merge from opposite sides of a headland. If the arch collapses, a pillar of rock remains behind as a sea stack.
  • Sea Terraces:
    • It is a rock terrace formed where a sea cliff, with a wave-cut platform before it, is raised above sea level.

Depositional Coastal Landforms

• Beaches:
  • Beaches are deposits of loose sediment adjacent to a body of water. In addition to sand, beaches around the world have a remarkable diversity of sediment size, from boulders to fine silt.
• Spits and Bars:
  • Spits:
    • A sand spit is a linear accumulation of sediment that is attached to land at one end.
    • They usually develop where the coastline bends inland from the longshore drift direction. The spit follows the longshore direction of the updrift coast.
  • Bars:
    • Sandbar, also known as Offshore Bar, is a ridge built by waves offshore from the beach, usually submerged or partially exposed.

What are the Landforms Formed by Glaciers?

• Glaciers have played a major role in the shaping of landscapes in the middle and high latitudes and in alpine environments. They are remarkably effective at eroding soil and rock, transporting sediment, and depositing sediment.
• A glacier is a mass of ice that moves over land as sheets (continental glacier or piedmont glacier) or as linear flows flowing down slopes of mountains into valleys (mountain and valley glacier).

Erosional Landforms formed by Glaciers

• Glacial Valleys/Troughs:
  • These valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides.
    • The valleys may contain littered debris or debris shaped as moraines with swampy appearance.
    • Very deep glacial troughs filled with sea water and making up shorelines (in high latitudes) are called fjords/fiords.
• Cirques:
  • Often found at the heads of glacial valleys, these are the most common of landforms in glaciated mountains.
    • They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at its head as well as sides.
    • A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque lakes or tarn lakes.
• Horns and Serrated:
  • Ridges Horns form through headward erosion of the cirque walls.
    • If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.

Depositional Landforms formed by Glaciers

• Glacial Till:
  • The unassorted coarse and fine debris dropped by the melting glaciers is called glacial till.
    • Some amount of rock debris small enough to be carried by such melt-water streams is washed down and deposited.
      • Such glaciofluvial deposits are called outwash deposits.
      • The outwash deposits are roughly stratified and assorted.
• Moraines:
  • They are long ridges of deposits of glacial till.
    • Terminal moraines are long ridges of debris deposited at the end (toe) of the glaciers.
    • Lateral moraines form along the sides parallel to the glacial valleys.
    • Many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors called ground moraines.
    • The moraine in the centre of the glacial valley flanked by lateral moraines is called medial moraine.
      • They are imperfectly formed as compared to lateral moraines.
      • Sometimes medial moraines are indistinguishable from ground moraines.
• Eskers:
  • These are ridges made of sands and gravels, deposited by glacial meltwater flowing through tunnels within and underneath glaciers, or through meltwater channels on top of glaciers.
    • Over time, the channel or tunnel gets filled up with sediments. As the ice retreats, the sediments are left behind as a ridge in the landscape.
• Drumlins:
  • They 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.
    • They may measure up to 1 km in length and 30 m or so in height.
    • The drumlin end facing the glacier is called the stoss end and is blunter and steeper than the other end called tail.

Landforms made by Winds
Erosional Landforms formed by Wind
Deflation Hollows	Formed by the removal of particles by wind.
Caves	Formed when blowouts formed by winds become deeper and wider and fit to be called caves.
Yardangs	Parallel troughs cut into softer rock running in the direction of the wind, separated by ridges.
Zeugen	Tabular mass of resistant rock, standing prominently in the desert.
Playas	Flat-bottom depression found in interior desert basins and adjacent to coasts in arid and semiarid regions, periodically covered by water.
Depositional Landforms formed by Wind
Ripples	Regular, wavelike undulations lying at right-angles to the prevailing wind direction.
Loess	Terrestrial sediment composed largely of windblown silt particles made of quartz.
Dunes	Collections of loose sand built piecemeal by the wind.
Coastal Landforms
Erosional Coastal Landforms
Cliffs	Vertical precipice created by waves crashing directly on a steeply inclined slope.
Sea Caves	Form along lines of weakness in cohesive but well-jointed bedrock.
Sea Stacks	Forms when sea caves merge from opposite sides of a headland
Sea Terraces	Forms where a sea cliff, with a wave-cut platform before it, is raised above sea level.
Depositional Coastal Landforms
Beaches	Deposits of loose sediment adjacent to a body of water.
Spits	Linear accumulation of sediment that is attached to land at one end.
Bars	It is a ridge built by waves offshore from the beach, usually submerged or partially exposed.
Landforms Formed by Glaciers
Erosional Landforms formed by Glaciers
Glacial Valleys/Troughs	Trough-like and U-shaped with broad floors and relatively smooth, and steep sides
Cirques	They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls.
Horns and Serrated	Ridges Horns form through headward erosion of the cirque walls. If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.
Depositional Landforms formed by Glaciers
Glacial Till	Formed when unassorted coarse and fine debris dropped by the melting glaciers.
Moraines	They are long ridges of deposits of glacial till.
Eskers	These are ridges made of sands and gravels, deposited by glacial meltwater flowing through tunnels within and underneath glaciers.