The geological cycle |
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1.- Evolution of the relief
The geological cycle is the group of processes that take place in the interior and the outside of the planet (geologic agents) and continuously modify its relief, destroying and reconstructing it simultaneously. The action of external and internal geological agents takes place thanks to the geologic processes, then classified in:
- External geological processes:
- Erosion: is the gradual wearing away process of the rock carried out by water, ice, atmosphere and living beings.
- Transport: displacement of the materials dislodged by the erosion towards the lowest zones of the relief. Light particles usually go further than the heavy ones.
- Sedimentation: accumulation of sediments in sedimentary basins when the transporting agent stops acting. The resulting sediments can become sedimentary rocks by a process called diagenesis.
- Internal geological processes:
- Metamorphism: group of transformations that change some minerals into another ones without melting them. Those transformations are caused by high pressures and temperatures.
- Magmatism: is the group made up by magma formation processes and the resultant rocks (igneous rocks). Those rocks are classified in three categories:
- Plutonic rocks: these are originated by slow cooling of a magma deep inside the crust. They have got big crystals as a result of the very slow cooling process.
- Filonian rocks: are originated by slow cooling inside cracks in the crust. The have big cristals.
- Volcanic rocks: they appear by fast cooling of magmas on the surface after a vulvanic eruption. They usually have got small crystals, and in some cases they don't have crystals at all.
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