The earth’s surface is being continuously subjected to by external forces originating within the earth’s atmosphere and by internal forces from within the earth. The external forces are known as exogenic forces and the internal forces are known as endogenic forces. The actions of exogenic forces result in wearing down (degradation) of relief/elevations and filling up (aggradation) of basins/depressions, on the earth’s surface whereas endogenic forces continuously elevate or built up parts of the earth’s surface.
Geomorphic Processes Endogenic and Exogenic Process
The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes.
A Geomorphic Agent is that mobile medium which removes, transports and deposits earth materials.
The energy emanating from within the earth due to radioactivity, rotational and tidal friction and primordial heat from the origin of the earth constitutes the main force behind endogenic geomorphic processes. Volcanism and Diastrophism are the two main endogenic processes.
All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. They include
- Orogenic Processes: Mountain building
- Epeirogenic Processes: Upwarping of Crust (Continent building process)
- Plate Tectonics
- Fold Mountains: Fold Mountains are mountains that form mainly by the effects of folding on layers within the upper part of the Earth's crust. Fold mountains form when two tectonic plates move towards each other at a convergent plate boundary. Examples: The Alps, the Himalayas, The Jura Mountains, the Zagros, the Appalachians, the Rockies, the Andes. They are closely associated with Volcanic activity and a source of rich mineral resources.
- Block Mountains: Block Mountains are formed as the result of faulting caused by tensile and compressive forces motored by endogenic forces coming from within the earth. Example: the Hunsruck Mountains, the Vosges and Black Forest of Rhineland, the East African rift valley system.
- Volcanic Mountains: These are formed due to successive accumulation and deposition of volcanic materials falling around the vent. Example: Mt. Fuji, Mt. Mayon etc
- Residual Mountains: Evolution of mountains after the denudation process. Example: Monadnock of the US, the Aravallis etc
Volcanism includes the movement of molten rock (magma) onto or toward the earth’s surface and also the formation of many intrusive and extrusive volcanic forms.
Landforms of Igneous intrusions
- Sill: Horizontal intrusion of Molten Magma
- Dyke: Vertical intrusion of Molten Magma
- Laccolith: These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below
- Lopolith: Saucer-shaped landform with concave upwards
- Phalcolith: A wavy mass of intrusive rocks found at the base of synclines or at the top of the anticline.
- Batholith: A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
Types of lavas
- Basic Lava
- Hottest lavas, highly fluid
- Dark coloured, rich in Fe and Mg but poor in Si
- They flow Quietly over large extensive areas in thin sheets resulting in Shield Volcano
2. Acid Lava
- Highly Viscous with a high melting point
- Light coloured, low density, has a high percentage of Si
- They form steep cones, very violent in nature
Types of Volcanos
- Active: they frequently erupt or have erupted in recent times
- Dormant: they have been known to erupt and show signs of the possible eruption in the future
- Extinct: Volcanoes that have not erupted at all in historic times but retain the features of Volcanoes
- Basalt Province: formation of lava plains and plateau when lava flows over a long distance
- Lava dome or Shield Volcanoes: Formed due to highly fluid lavas
- Lava dammed lakes, lava tongues, lava bridges, lava tunnels
- Lava materials: Pyroclasts, lapilli, scoria, purnice, volcanic bombs
- Caldera lake: Depression formed due to a violent eruption which may be later filled with water.
World distributions of Volcanos
Source: Online geography
Hot Springs and Geysers
Geysers are fountains of hot water and superheated steam that may sprout upto a height of 150m from the earth beneath.
They are confined to three major areas
- The Rotorua district of North Island, NZL
- The Yellowstone Park, Wyoming – Old Faithful geyser
Hot Springs are found in any part of the earth where water sinks deep enough beneath the surface to be heated by the interior forces. They rise to the surface without any explosion.
Denudation is the process of wearing away the earth resulting in a general lowering and leveling out of the surface. The process is carried out in four phases
Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate.
- Chemical: the extremely slow and gradual decomposition of rocks due to exposure to air and water.
(i) Solution: Solubility of the mineral into water or acid resulting in the removal/disintegration of rock matter. C02 dissolves in water forming weak Carbonic acid which affects the Karst topography
(ii) Carbonation: Carbonation is the reaction of carbonate and bicarbonate with minerals and is a common process helping the breaking down of feldspars and carbonate minerals.
(iii) Hydration: Hydration is the chemical addition of water. Calcium Sulphate takes water and turns into Gypsum which is more unstable than Calcium Sulphate
(iv) Oxidation and Reduction:
Oxidation refers to the combination of a mineral with oxygen to form oxides or hydroxides. Example: Red iron turns into brown or yellow due to oxidation.
In Reduction oxidized minerals are placed in an environment where oxygen is absent. Example: Red color of iron upon reduction turns into greenish or bluish grey.
- Physical Weathering: they are dependent on some applied forces such as Gravitational force, expansion forces, water pressure etc. the weathering process is caused by thermal expansion and pressure release.
(i) Unloading and Expansion: Removal of Superincumbent load results in the expansion of upper layers and disintegration of rock masses. Exfoliation process takes place resulting in Exfoliation domes.
(ii) Temperature changes and Expansion: Diurnal changes in temperature, especially in desert regions where the outer layer expands and contracts more rapidly than the inner layers sets up internal stress and disintegration.
(iii) Freezing, Thawing and Frost Wedging: Accumulation of water in the cracks and crevices of rocks and their freezing leads to building up of stress in rocks and consequent weathering.
(iv) Salt Weathering: Salts in rocks like Calcium, Sodium, Magnesium, Potassium etc expand in rocks due to thermal action, hydration and crystallization. This process results in Granular disintegration.
- Biological Weathering: Biological weathering is a contribution to or removal of minerals and ions from the weathering environment and physical changes due to growth or movement of organisms. Example: Decaying plants and animal matters, burrowing animals, human actions etc
These movements transfer the mass of rock debris down the slopes under the direct influence of gravity. Mass movements are aided by gravity and no geomorphic agent like running water, glaciers, wind, waves and currents participate in the process of mass movements.
- Slow Movement
- Soil Creep: Movement of material is extremely slow and imperceptible.
- Solifluction: Slow downslope flowing soil mass or fine-grained rock debris saturated or lubricated with water.
- Rapid Movement
- Landslides: they are relatively rapid and perceptible movements with relatively dry materials. They are further categorized into Slump, debris slide and rock slide.
2. Earthflow: Movement of water-saturated clayey or silty earth materials down low-angle terraces or hillsides is known as earthflow.
3. Mudflow: In the absence of vegetation cover and with heavy rainfall, thick layers of weathered materials get saturated with water and either slowly or rapidly flow down along
definite channels. It looks like a stream of mud within a valley.
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