Landforms and their evolution

Landforms are the natural process of the earth’s surface that includes mountains, hills, plateaus, and plains. Landforms consist of their own physical shape, size, materials. These are the results of certain geomorphic processes and agents.

Landforms may change their shape, size, and nature after their formation as a result of the continued action of geomorphic processes and agents.

Evolution of Landforms: It implies stages of transformation of either a part of the earth’s surface from one landform into another or transformation of individual landforms after their formation.  Landmass passes through stages of development as young, mature, and old age.

Here we discuss:

  • Running water landforms
  • groundwater landforms
  • Glacier landforms
  • Wave and current landforms
  • Wind landforms
Landforms and their evolution

Landforms

Running water landforms

The running water landforms are the result of heavy rainfall, running water, and the fast running water of rivers.

  • Most erosional landforms are made by running water are associated with youth rivers flowing along steep gradients.
  • Depositional landforms are mainly associated with rivers flowing over medium to gentle slopes.

Erosional Landforms of Running Water:

Valleys: These are formed by rills. The small rills gradually develop into long and wide gullies and finally, the gullies deepen, widen, and lengthen to give rise to valleys. Valleys can be of:

  • V-shaped valley: These are created by fats flowing rivers in the upper course of the river with steep gradients.
  • Gorge (in hard rocks): It is a deep valley with very steep to straight sides. It is almost equal in width at its top as well as its bottom.
  • Canyon (In soft rocks): It is a variant gorge, characterized by steep step-like side slopes and may be as deep as a gorge. Its top is wider than the bottom.

Potholes and Plunge Pools: Potholes are more or less circular depressions formed over the rocky beds of hill streams, due to stream erosion aided by the abrasion of rock fragments. Such a series of depressions eventually join and the stream valley gets deepened.

Plunge pools are formed by large and deep potholes at the foot of waterfalls. Plunge pools help in the deepening of valleys.

Incised or Entrenched Meanders: Because of active lateral erosion, streams flowing over gentle slopes develop sinuous or meandering courses. The deep and wide meanders found in hard rocky terrain are known as incised or entrenched meanders.

River Terraces: These are surfaces that mark the old valley floor of floodplain levels. They are bedrock surfaces without any alluvial covers or alluvial terraces consisting of stream deposits.

The river terraces may occur at the same elevation on either side of the rivers in which are called paired terraces.

Depositional Landforms of Running Water:

Alluvial Fans: These formed due to streams flowing from higher-level break into foot slope plains of low gradient.

Deltas: These are the large roughly triangular bodies of sediment deposit at the mouth of a river. As the delta grows, the river distributaries continue to build up into the sea.

Flood plains: It is a major landform of river deposition.

  • A river bed made of river deposits is the active flood plains.
  • The flood plain above the bank is an inactive flood plain. The flood plains in the delta are called delta plains.

Natural Levees: These are found along the banks of large rivers. The natural levees are low, linear, and parallel ridges of coarse deposits along the banks of rivers and quite often cut into individual mounds.

Point Bars: The points bars are also called meander bars. These are found on the concave side of meanders of large rivers and are sediments deposited in a linear fashion by flowing water along the bank.

Meanders: The meanders are loop-like channel patterns developed over large flood and delta plains.

Ground water landforms

Formation of Karst Landforms:

The landforms produced by the action of groundwater through the chemical process of solution and precipitation deposition develop verities of landforms in rocks like limestones or dolomites which are rich in calcium carbonate. These two processes of solution and precipitation are active in limestone or dolomites occurring either exclusively or interbedded with other rocks.

  • The landforms produced by the action of groundwater in limestone or dolomitic region through the processes of solution and deposition are known as Karst topography.
  • The Karst topography is named after the typical topography that develops in limestone rocks of the Karst region in the Balkans adjacent to the Adriatic Sea.
  • It is also characterized by erosional and depositional landforms.

Erosional Landforms of Karst Topography

Sinkholes: Small to medium-sized round to sub-rounded shallow depressions are called swallow holes that form on the surface of limestones through the solution. Sometimes swallow holes are also known as sinkholes. The sinkhole is an opening less or more circular at the top and funnel-shaped towards the bottom.

  • Pools: The sinkholes covered up with soil mantle have appeared as shallow water pools.
  • Doline: The dolines are collapse sinks.
  • Uvalas: When sinkhole and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, valley sink or uvalas form. The Uvalas are long and narrow trenches.
  • Lapies: These are formed when most of the limestone is taken away by the pits and trenches and leaving the surface extremely irregular with a maze of points, grooves, and ridges or lapies.

Depositional Landforms of Karst Topography

  • Stalactites: It is a column of pure limestone with different diameters hanging from the roof of a cave-like icicle. The stalactites are broad at their base and taper towards the free ends.
  • Stalagmites: It is a column of pure limestone with different diameters formed on the floor or rising up from the floor of a cave.
  • Pillars and columns: These are formed by the fusion of stalagmite and stalactites.
Glacier Landforms

The glaciers are the masses of ice. They move as sheets over the land eg. continental glacier or piedmont glacier. The glaciers move because of the force of gravity. The movement of glaciers is slower than water. The glaciers may be of following types:

Erosional Landforms of Glaciers

  • Cirque: These are the most common of landforms in glaciated mountains, often found at the head of glacial valleys.
    • A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes.
  • Horns and Serrated Ridges: The horns are formed by headward erosion of cirque walls. Example of horn: Matterhorn; the highest peak in the Alps, and Everest; the highest peak in the Himalayas are examples of Horns.
  • Glacial Valley/ Through: These are through like U-shaped having broad floors and relatively smooth and steep sides.
    • The glacial valleys contain littered debris or debris shaped as moraines with swampy appearance and lakes are formed by this debris within the valleys.
    • There can be hanging valleys at an elevation on one or maybe on both sides of the main glacial valley.
    • Very deep glacial troughs filled with seawater and making up shorelines are called fiords/fjords.

Depositional Landforms of Glaciers

  • Moraines: These are long ridges of deposits of glacial till. The terminal moraines are long ridges of debris deposited at the end of glaciers.
    • Many valley glaciers retreating rapidly leave an irregular sheet of till over their valley floors such as deposits varying in thickness and in surface topography are called ground moraines.
    • Medial moraines are the moraines in the center of the glacial valley flanked by lateral moraines.
  • Eskers: In summer the glaciers melt and the water flows on the surface of the ice or seeps down along the margins or even moves through holes in the ice. The water accumulates beneath the glacier flow like streams in a channel, such streams flow over the ground with ice forming its blanks. many miner fragments of rock debris carried into streams get settled in the valley of ice in the form of the sinuous ridges called eskers.
  • Outwash Plains: These are broad flat alluvial fans at the foot of the glacial mountains or ice sheets are covered with glacial – fluvial deposits.
  • Drumlins: These are smooth oval-shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand.
Landforms of Waves and currents
  • Erosional landforms of Waves and currents
  • Depositional landforms of waves and currents

Erosional landforms of waves and currents

  • Cliff and Terraces: These are found at the place where erosion is the dominant shore process. The cliffs are steep ranges from a few meters to 30 meters. The foot of such cliffs may be flat or gently sloping platforms covered by rock debris derived from the sea cliff behind. These platforms occurring at elevations above the average height of waves is called wave-cut terrace.
  • Caves: These are large natural hollows in the cliff along the coast with horizontal openings. The caves are formed by the lashing of waves against the base of the cliff and the smashing of rock debris against the cliff.
  • Stacks: The masses of rocks, originally the parts of cliff or hill are called sea stacks.

Depositional landforms of waves and currents

  • Beaches and Dunes: The beaches are characteristics of shorelines that are dominated by deposition, occur as patches along even the rugged shores.
    • Most of the beaches are made up of sand-sized materials.
  • Bars: These are ridges of sand and shingle built in the sea in the off-shore zone, which lies parallel to the coast is called off-shore bar.
  • Barriers: It is the place where the offshore bar is exposed. Due to further addition of sands the offshore bar is exposed is termed as barriers.
  • Spits: When the bars get keyed up to one end of the bay, then it is termed as spits.
Wind Landforms
  • Erosional landforms of wind
  • Depositional landforms of wind

Erosional landforms of wind

  • Pediments: These are rocky floors close to the mountains at their foot with or without a thin cover of debris. The pediments are formed due to erosion of the mountain front through the combination of lateral erosion by the stream and sheet flooding.
  • Pediplains: These are formed with steep wash slop followed by cliff or free face above it.
  • Playas: These are mostly found landforms in deserts. Water retains for a short duration due to evaporation in playas. The playa plains are covered up by salts called alkali flats.
  • Deflation hollows: Sallow depressions created by the persistent movement of wind current in one direction are called deflation hollows.
  • Caves: abrasions in rock faces due to wind becoming deeper and wider are called caves.
  • Mushroom, table, and pedestal rocks: These are rock cuts by the wind in the beautiful shape of mushroom with a slender stalk and a broad rounded pear-shaped cap above. The top of the rock resembles a tabletop and the remnants stand out like pedestals.

Depositional Landforms of wind

Sand dunes: These are very often in the dry hot deserts, these may be of various shapes: Crescent shaped dunes, Parabolic dunes, Seif, Longitudinal dunes, Transverse Dunes.

 

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