INTERNAL ENERGY AND LANDFORMS

WHY ARE ROCKS FORMED?INTERNAL ENERGY The deformation of rocksThe movements of the Earths 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

FaultsFaults are fractures in the rocks of the Earths crust where blocks have been displaced. (Tectonic forces are greater than resitstance).Types: Dip-slip faults: movement is vertical: Normal, reverse and verticalStrike-slip faults: movement is horizontal: Sinistral tear and dextral tear fault.

FaultsNormal faultReverse

Strike slip faults

FoldsFolds are created when rocks deform but they dont break.

Fold class

External geological processesCaused by Solar EnergyWeatheringErosionTransportationSedimentationDiagenesis

Internal geological processesThose come from the internal heat and pressure inside the Earth.Magmatism and tectonic plates: The internal heat creates magma and produces volcanoes, geysers and thermal springs.Geothermal gradient: 30C/Km (average)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 frictionA drop in pressure reduces the melting pointThe presence of liquids reduces the melting pointMagma 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.Internal geological processesMetamorphism 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 metamorphismContact or thermal: produced by an increase of T.Regional or dynamothermal: produced by an increase of T and P.Dynamic metamorphism: produced by an increase in P.Formation of mountain rangesAccording to Tectonic Plates Theory 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 orogensThe collision of terranes (fragments of crust surrounded by faults) is produced when small ridges in the oceanic plates reach the trench. But here subduction doesnt stop. As a consequence, an accretion orogen is formed on the edge of the continent as successive fragements are added. IsostasyIsostasy 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.IsostasyIsostasy 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 activitySeismic risk

Volcanic risk

Types of eruptions