The earth is divided like a puzzle a series of compartments called rigid lithospheric plates.

Classified in Geology

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1-internal geologic agents:

internal geologic agents: they are the movements of the lithospheric plates, earthquackes and volcanic eruptions. These agents build the earth's relief. The energy resource that lets them to work is the heat stored inside the earth, prof os this heat is the geothermal gradients defined as the increase of temperature with depth. This heat is due to: 
-the collision of planetesimals during the earth's formation
-the disintegration of radioactive elements.

2.Movement of lithospheric plates
the earth can be divided into three layers(from a dynamic point of view):
-lithosphere: is the rigid outermost layer. It is composed of the crust and a little portion of the upper mantle(from 0 to 100 km).
-mesosphere: is the rest of the mantle. Its a semiliquid layer.
-endosphere: consists of the core(outer and inner core).

lithosphere is not a continous layer, but is divided into pieces just like a puzzle, forming the lithosphere plates. There are three types of lithosphere plates depending on the kind of crust they are formed by:
-continental plates: they are formed by the continental crust and a portion of the upper mantle(arabian plate)
-oceanic plates: they are formed by the oceanic crust and a portion of the upper mantle(pacific plate, nazca plate)
-continental/oceanic plates: they are formed by both continental and oceanic crust and a portion of the upper mantle(indoaustralian platelet, north america...).

A)divergent boundary: the two plates move away from each other. Volcanic activity is common in these areas since mantle easily moves to the surface through the thin, fractured rock as it separates. This happens all along the mmid ocean ridge where magma is constantly streaming to the surface, creating new ocean floor as the plates separate(the atlantic ridge is between the american plate and african and eurasian plates). Oceanic crust is created

B) convergent boundary: when both plates are pushing into each other. Depending on the kind of crust colliding, two things can happen:
-oceanic plate-continental plate: as oceanic crust is denser than continental crust, the former slides down(causing earth quackes because of friction) under the latter, and it is melted. The melted materials rise and a line of volcanoes are formed on the continental crust. The place that collides are called subduction zones (mariana trench)

-continental plate-continental plate: high mountains are formed in these areas ( himalaya)

C) transform boundaries: where plates slide past each other causing earthquackes.

apart from these type of boundaries are other forms of volcanic activity: the hotspots: there are places far from the plate boundaries where magma rises from the mantle to the surface forming volcanoes.

3-earthquackes
they are the movements of the ground due to releasing of energy from fractured rocks in the crust when platelets move. Energy released as seismic waves. The hypocentre is the point within the earth where an earthquacke starts. The epicentre is the point at th surface of the earth directly above the hypocentre

4-volcanoes
a volcano is a fracture in the crust that allows magma to escape to the surface. Magma is a mixture of melted rocks, solid fragments are dissolved in gases.

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