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Unit2.EARTH’SRELIEF 1. THEEARTHSTRUCTURE • • • Crust.ItisthemostexternalandthinnestlayeroftheEarth. – Continental crust. It is composed by the emerged lands. It can reach up to 20 or 70 km. Its main composition is based on rocks andsands. – Oceaniccrust.Itiscomposedbythelandthatissubmergedunder thesea.Itonlyreaches10kmundertheoceans. Mantle. It is mostly composed of magma (molten rock) and constitutes the70%oftheEarth’sthickness.Itisnotarigidlayer. Core.ItisthecentralpartoftheEarthandiscomposedofheavymetals, iron,andnickel.Itisdividedinuppercoreandinnercore 2. ¿CÓMOSECONSTRUYEELRELIEVE?Pág32y33(castellano) 3. RELIEFEXTERNALAGENTS • Thereliefchangesdueto: • • • • Erosion.Rockswearawayandtheydissolve. Carriage:Itcarriesalltheerodedmaterialsfromtherocks. Sedimentation:Itdepositsalltheerodedandcarriedmaterials. Although the tectonic plates formed the relief there are other external agentsthatmodifiesthereliefas: 1. Water 2. Wind 3. Temperatures 4. Vegetation 5. Humanbeings 1. Water: it is a constant action over the rocks. It can be stronger dependingonthekindofstone(limestonecanbeerodedmoreeasily). – Rain.Itcancreatevalleysandravines(barrancos). – Rivers.Theyhavedifferentpartswheretheerosionchanges.Itis harder in the upper course due to the slope and the speed of waters. Instead it is very scarce is the lower course, since the speedoftheflowismuchsmaller. – Sea. Waves and currents cause different coastal geological formationssuchascliffsorbeaches. – Groundwater.Itcancausecavesandundergroundrivers. • Rivers born in the mountains where form valleys and fluvial terraces. • Valleys:Theyhavebeencreatedbytheriversintheirflow towards their mouth. They are usually low lands between mountains. Fluvialterracesareflatareaslocatedneartheriver Groundwater.Itcancausecavesandundergroundrivers. Glacier:frozenwaterformslakesinthemountains 1. The wind: It wears away the rocks and detaches some particles that attack other rocks, polish and model them. It is called aeolian or wind erosion. Dunes are the most typical formations created by aeolian erosion. 2. Vegetation.Mostofthetimes,plantshelpfixsoilbuttheirrootscanalso splitrocks. • • • 3. Humanbeings.Wetransformenvironmentforagriculture,stockbreeding, cities,felling,reservoirs,fires,mining... 4. CONTINENTALRELIEF. Thecontinentalreliefisthegeographicalformationswhichcoverthecontinents. • Mountains.Theyareelevationsofthelandwithdifferentorigin. – Theywerecreatedduringtheorogeniessomemillionsyearsago. – The highest mountains emerged in more recent periods. Their profilesaresteeper. – The oldest mountains are lower and rounder. They are called massifs.Theyusedtobehighbuttheywereeroded. • Mountainrange:geographicalareacontainingnumerousmountains.The mountainrangeisalsoknownasmountainsystem. – The highest mountain range are the (Everest is the highest mountainintheworld,8,848m). – The longest mountain range is the Andes (together with Sierra MadreandtheRockyMountains). • Hill:smallmountain. • Plateaux/Mesetas.Theyarelargeflathighareashigherthan400metres. – ThehighestplateauxintheworldaretheTibetanPlateauandthe Altiplano(Bolivia),theyexceed3,000metreshight. • Plains. They are usually along the coast (coastal plains) or by the rivers (riverplains). • Valleys.Theyhavebeencreatedbytheriversintheirflowtowardstheir mouth.Theyareusuallylowlandsbetweenmountains. • Depressions: They are large areas located below sea level, such as the Deadsea(-395m),DeathValley(-86m)ortheCaspianSea(-28m). 5. COSTALRELIEF: Thecostalreliefiscomposedofseveraltypes: • Beaches: They are geological landforms along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composedofrock,suchassand,gravel,shingle,pebblesorcobblestones. • Cliffs:theyareasignificantvertical,ornearvertical,rockexposure. Baysandgulfs:Theyareareasofwatermostlysurroundedbyland.Gulfs arebiggerthanbays. • Capes:Theyarepointsorbodiesoflandextendingintoabodyofwater, usuallythesea. • Peninsula: piece of land that is bordered by water on three sides but connectedtomainlandthroughanisthmus. • Islands:Areaoflandcompletelysurroundedbywater.Ofthereisagroup ofislandsitiscalledarchipielago • Marshlands. They are a type of wetland that is subject to frequent or continuousflood. Elrelievedelosfondosmarinos.Pág37(castellano) •