The EXTERNAL GEOLOGICAL AGENTS are natural systems that carry out different geological processes. They modify, alter or transform the surface of the planet and produce characteristic landforms (they carry out the process of modelling the land relief).
They are dynamic agents
because they have the ability to move, and they act thanks to the solar energy of the sun (the energy
of the sun makes air masses move and this causes the water cycle with precipitation).
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There are SIX MAJOR GEOLOGICAL AGENTS which are:
1.-
WIND: It´s air moving on the Earth surface. It acts mainly in
areas with no vegetation like the deserts and beaches.
Also, the wind is capable of eroding, transport and
sediment. Wind can transport materials and vegetation anywhere on the planet.
On the one hand, the wind's ability to erode is due to the sand that it transports, which, when colliding with the rocks, wears them down. On the other hand, the sand carried by the wind is depositedin certain areas, forming dune fields. Dunes are large accumulations of sand that move and move slowly in the direction of the wind.
The main landforms produce by the wind are: pedestal rocks, regs and barchans.
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In the upper course of the river, the slope is greater and erosion
and transport processes dominate. In the middle course the slope decreases. Although the river retains
a certain capacity to erode and transport materials, begins to sediment eroded
material upstream. In the lower course the slope is very gentle, the
river practically loses its ability to erode and only deposits sediments.
The main landforms produce by rivers are: meanders, V-shaped valleys and deltas.
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4.- OCEANS: they cause coastal erosion along the shore line removing materials from the coastline and sometimes forming cliffs where we can see the great capacity of erosion of the water. They also carry rivers sediments.
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The waves erode the rocks in the area littoral, transport the
produced sediment and deposit it later. This causes different effects of
erosion and sedimentation.
Currents and tides also produce processes of erosion, transport and
sedimentation due to fluctuations in sea level.
The main landforms produce by marine sedimentation are: sand bars, sand spits, salt marshes, coastal lagoon, beaches and tombolo.
5.- GROUNDWATER: In the water cycle, a part of which precipitates over
the continents infiltrates into the subsoil, through permeable rocks, until
finding a layer of rock waterproof that retains it. Groundwater is water that flows downward influenced by
gravity and it can dissolve (due to the
acidity) soluble underground rocks and it can form, galleries, chambers, limestone pavement, caves, stalatites, dolines,
potholes, etc.
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6.- SURFACE RUN OFF: excess of water (rain, melted snow or other waterflows
over the land surface) that flows over that land. It has a bigger capacity of
erosion in areas in which doesn’t usually rain and torrential rains. It can
create: ravines, gorges, rills, gullies…
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