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INTERNAL ENERGY
WHY ARE ROCKS FORMED?
The deformation of rocks
 The movements of the Earth’s plates generates forces or
STRESSES on the rocks of the lithosphere which cause
deformations or changes in these rocks.
 Compressional stess: comes from opposing convergent
forces. (squeeze)
 Tensional or extensional: comes from opposing and divergent
formces. (stretch)
 Shear stress: from parallel forces, convergent and divergent.
(tear)
DEFORMATIONS
Faults
 Faults are fractures in the rocks of the Earth’s crust where
blocks have been displaced. (Tectonic forces are greater than
resitstance).
 Types:
1. Dip-slip faults: movement is vertical: Normal, reverse and
vertical
2. Strike-slip faults: movement is horizontal: Sinistral tear and
dextral tear fault.
Faults
Normal fault
Reverse
Strike slip faults
Folds
Folds are
created when
rocks
deform but
they don’t
break.
Fold class
External geological processes
 Caused by Solar Energy
1.
2.
3.
4.
5.
Weathering
Erosion
Transportation
Sedimentation
Diagenesis
Internal geological processes
 Those come from the internal heat and pressure inside the
Earth.
1. Magmatism and tectonic plates: The internal heat creates
magma and produces volcanoes, geysers and thermal
springs.
2. Geothermal gradient: 30ºC/Km (average)
3. High pressures rise the melting point and keep the rock
solid.
Melting….
 Melting can be produced in places due to some mechanisms:
A rise in temperature prodeced by friction
2. A drop in pressure reduces the melting point
3. The presence of liquids reduces the melting point
Magma from deep mantle is released at mid-ocean ridges, rifts
and hot spots.This magma is rich in iron and magnesium
and has a low fluid content.The magma from the
subduction zone comes from the molten crust and is rich in
silicon, alumninium and gases.
1.
Internal geological processes
 Metamorphism and tectonic place:
 It is a process where the type or distribution of minerals in
rocks changes because if high pressure or very high
tempreratures. It is called isochemical because the
composition of the rock remains unchanged.
 Metamorphism can sometimes occur in faults or at the sites
of meteor impact.It is also found in areas with convergent
plate boundaries, such as subduction and continental collision
zones.
 Metamorphic belts: next to the trench and in the volcanic
arc.
Types of metamorphism
 Contact or thermal: produced by an increase of Tº.
 Regional or dynamothermal: produced by an increase of Tº
and Pº.
 Dynamic metamorphism: produced by an increase in Pº.
Formation of mountain ranges
 According to Tectonic PlatesTheory there are two types of
orogens: Orogens associated with subduction zones and
orogens associated with continental collisions.
Orogens: continental colission and
subduction
More orogens…
Accretion orogens
Accretion orogens
 The collision of terranes (fragments of crust surrounded by
faults) is produced when small ridges in the oceanic plates
reach the trench. But here subduction doesn’t stop. As a
consequence, an accretion orogen is formed on the edge of
the continent as successive fragements are added.
Isostasy
 Isostasy is the state of equilibrium between the lithosphere
and the plastic mantle: if the weight of the lithosphere
increases it usually sinks into the mantle; if its weight
decreases, the lithosphere normally rises.
Isostasy
 Isostasy associated with
glaciation: the weight of an
ice cap causes part of the
lithosphere to sink. When
the ice melts, the
lithosphere rises and
recovers its initial
equilibrium.
 Isostasy related witn
erosion and deposition: the
bottom of a basin tends to
sink when a thick layer is
deposited (subsidence).
When it is eroded, the
opposit process occurs.
Risks associated with geological
activity
Seismic risk
Volcanic risk
Types of eruptions