Various Types of Landforms
Landforms are defined as the geomorphologic units defined by its surface form and location in the landscape. Landforms are typical elements of the topography. The water body interfaces also called landforms. They are categorized on the basis of elevation, slope, orientation, stratification, rock exposure, and soil types as follows:
- Aeolian landforms
- Coastal and oceanic landforms
- Erosion landforms
- Fluvial landforms
- Mountain and glacial landforms
- Slope landforms
- Volcanic landforms
- Aeolian landforms
- Fluvial Landscapes
- Erosional Landforms
- Landforms made by River Erosion
- Landforms made by River Deposition
- Landforms made by River Transportations
Aeolian landforms refer to the Landforms that are formed by the winds. There are two types of the Aeolian Landforms viz. Erosional and Depositional.
Aeolian Landforms: Erosional
Zeugen or Rock Mushrooms
They are also known as rock pedestal or a pedestal rock or Zeugen. Usually Found in Desert Areas.
Yardangs form in environments where water is scarce and the prevailing winds are strong, unidirectional and carry an abrasive sediment load. They consist of an elongated ridge carved by the unidirections erosion.
Dreikanter exhibits a 3 faced Pyramidal Shape. They typically form in Deserts due to wind erosion.
Blowouts refer to sandy depressions in a sand dune ecosystem, which are caused by the removal of sediments by wind.
Inselbergs refer to the prominent steep sided hill of solid rock rising abruptly from a plain of low relief. Inselbergs are generally composed of resistant rocks such as Granites.
Desert pavement refers to mountain wash containing pebbles, gravels and sand particles exposed to wind and surface appears as a pavement with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size
Aeolian Landforms: Depositional
Erg or Sand Sea
Erg is a sand sea or a dune sea. They are flat area of desert covered with wind-swept sand with little or no vegetative cover. The area is generally more than 100 square miles and is deposited by windblown sand. Largest Hot Desert in the World viz. Sahara has several sand Seas. The Ergs have 85% of Earth’s mobile sand.
Ripples are well marked small waves produced on the surface of sand, mud and even rock by the drag of the wind / water moving over it. They are most common in deserts.
Barchan refers to crescent shaped dunes, which have tips or horns pointing downwards. Barchans are found in desert areas which have low sand quantity.
Longitudinal dunes are also known as Seif dunes. Seif is a arabic word for Sword. These are long, slightly sinuous, ridge shapped dunes which are parellel to the wind direction, elongate parallel to the prevailing wind, possibly caused by a larger dune having its smaller sides blown away. Seif dunes are sharp-crested and are common in the Sahara.
Transverse Dunes are asymmatrical sands in deserts which are at right angle to the wind direction. They are most probably caused by a steady build-up of sand on an already existing minuscule mound.
Star Dunes are giant star shapped dunes with 3 or more sinuous arms extending outwards from the center. These shapes can alter due to windspeeds.
The landforms which develop as a result of the water action are known as Fluvial Landforms. Running water such as rivers are the most important agent of erosion. Other agents such as Glaciers, Groundwater, wind and sea water are locally dominant agents of erosion. The Fluvial processes are most important of all the exogeneric processes as landforms associated with them have overall dominance in the environment of terrestrial life. These fluvial processes can be divided into three phases viz. erosion, transportation and deposition.
The Erosion can be normal erosion which takes place by the natural physical processes or the Accelerated Erosion, which is produced by human interference. The Sheet Erosion refers to the surface flow removing soil in thin layers. It can be accelerated in the Steep slopes, where innumerable closely spaced channels are formed, which grows larger form in gullies (steep-walled canyon like trench). The Erosion can be of following types:
- Chemical erosion: Corrosion (Or solution) and carbonation.
- Mechanical erosion.
- Impaction (effect of blow upon the river bed or banks by large boulders).
- Cavitations (shattering and breaking up of the stream load through collisions and mutual abrasion).
- Hydraulic action (lifting and quarrying effect of rushing water).
- Corrosion or abrasion (stream uses its load to scrape away its bed, particularly in steep confined sections of stream channels).
Landforms made by River Erosion
Valley starts as small and narrow rills which gradually develop into long and wide gullies. The gullies will further deeper widen and lengthen to give rise to valleys which is V-shaped. The River valley is an important erosional landform. They are formed in the youthful stage of fluvial cycle of erosion. The vertical erosion or valley deepening causes the V-shaped valleys.
Gorge & Canyons
The V-shaped valley can be a Gorge, where steep precipitous wall within which a narrow river is confined (e.g. – Indus, Sutlej, Brahmaputra, Rhine, Zambezi). Thus, we can say that Gorge is a V-shaped valley but its sides becomes so steep that they look almost vertical. Or it can be a Canyon, which is basically a very deep and extended gorge. The Grand Canyon in Arizona, United States of America is the largest Canyon in the world.
The meanders or meandering rivers are the low slope rivers which are not choked with the sediment and move back and forth in a zig-zag order of loops. The meander has thus a serpentine path and it helps in accommodating in extra volume of water.
River terraces are abandoned floodplains that formed when a river flowed at a higher level than it does today. Thus, these are the surfaces that mark an old valley floor or floodplain levels.
When an extensive area has been eroded sufficiently to give the look of almost a plain, it is called a Peneplain.
Landforms made by River Deposition
When the velocity of the running water, as it comes out of hills and meets the plain, decreases, it dumps the transported material at the foothills. The structure made are called alluvial fans. The alluvial fans are formed due to accumulation of materials in the form of fan and cones respectively at the base of foot hills Alluvial cones are made of coarse materials than the alluvial fans.
Narrow belt of ridges of low height built by the deposition of sediments by the spill water of the stream on its either bank.
Surfaces on either side of a stream that is frequently inundated.
Formed by breaching of leaves when water escapes through a series of distributaries channels.
Plain area adjoining a levee may contain marshes called back swamps.
Distributions of rivers occupying lateral positions.
Delta is the triangular deposition at the mouth of a river debouching in a lake or a sea. The Factors that help in delta formation are as follows:
- Long courses of rivers.
- Medium size sediments.
- Calm or sheltered sea.
- Suitable place (shallow sea and lake shores).
- Large amount of sediments.
- Stable condition of sea coast.
On the basis of shape delta can be divided into following categories such as arcuate, bird-foot, Estuarine, Cuspate, Truncated etc.
Arcuate (lobate form) Delta
The Arcuate delta resembles the fan and is convex towards the Sea. It is semicircular in shape and is commonly found in semi-arid region; growing delta such as Nile, Niger, Ganga, Indus, Mekong, Irrawaddy, Rhine, Volga, Danube, Rhone, Lena rivers.
Birdfoot Delta is also known as a finger delta. In these deltas, the sediments deposited are composed of those fine particles which are received from the limestone rocks. The rivers with high velocity carry suspended finer load to greater distance inside the oceanic water (such as Mississippi).
When a river enters the sea through the single mouth or estuary, then the Estuarine Delta is formed which is submerged under marine water. Examples are Narmada River, Congo River, Amazon River and Hudson River.
Cuspate delta are pointed. They are shaped by regular, opposing, gentle water movement as seen at the Tiber river.
The Oxbow lakes are formed by the depositional and erosional actions taking place simultaneously. Please note that excessive meandering would result in Oxbow lakes.
How Oxbow lakes are formed?
On the inside of the loop, the river travels more slowly leading to deposition of silt. Meanwhile water on the outside edges tends to flow faster, which erodes the banks making the meander even wider. Over time the loop of the meander widens until the neck vanishes altogether. Then the meander is removed from the river’s current and the horseshoe shaped oxbow lake is formed.
When the water spills out onto the flood plains, the heaviest material drops out first and finest material is carried over a greater distance. This fine grained alluvium would hold much water and would give rise to a wetland which is called Black swamps or simply swamps.
Landforms made by River Transportations
The dissolved solids in the rivers travel downstream and become a part of Ocean. The particles of clay, silt and fine grains are carried in suspension. Whenever a soft rock obstructs the course of stream and is eroded and sediments are scattered all around, it would be called Eddies. These Eddies sometimes look like discs and so are called potholes. The large potholes are called Plungepools.