Geography - Physical Geography Elective

CHAPTER 1 - GATEWAY 1

What is a natural hazard? naturally occurring events that threaten human lives and causes damage to property Tectonic natural hazard caused by plate movements when continental crusts and ocean floors move. earthquake volcanic eruptions Climate-related natural hazard caused by severe and extreme weather and climate conditions storms floods

INTERNAL STRUCTURE OF EARTH

Core mostly iron and nickel separated into liquid outer core and solid inner core about 3500km thick temperature between 3000 and 5000-degree celsius  Mantle mostly solid rock that flow under high temperature and pressure 2900km thick temperature between 800 and 3000-degree celsius Crust basalt and granite rocks a few km to more than 70km thick

!! lithosphere - crust & uppermost mantle rocks in lithosphere melt magma formed TYPE OF CRUST    1. Oceanic crust beneath deep oceans between 5 and 8km consists mainly basalt, heavy and dense rock formed by cooled magma rocks less than 200 million years old     2. Continental crust beneath earth's continental land masses and under shallow seas close to continents between 35 and 70 km consists of lighter rocks including granite rocks from recently to 4 billion years old

WHY DO TECTONIC PLATES MOVE?

 1. Convection currents movements of heat within the mantle. materials in the mantle heated by core mantle material expand, rise and expand beneath the plates            -this causes plates to be dragged along            -and move away from each other                          >hot mantle material cools slightly                          >sink and pull plates along                                         -sinking mantle material heats up again                                                near core                                         -whole process repeats

 2. Slab-pull force occurs when the dense, sinking oceanic plate at subduction zone pulls the rest of the plate behind it            -subducting or sinking plate drives downward-moving                     portion of convection current                          >mantle material away from where plates subduct                            drives rising portion of convection current   !! USE "PLATES" INSTEAD OF "CRUST" tectonic plates move a few cm a year

PLATE BOUNDARIES

  1. DIVERGENT Plates move away from each other Magma move to surface Cools to form new oceanic crust  2. CONVERGENT Plates move towards each other become faulted, folded and sometimes subducted  3. TRANSFORM  

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DIVERGENT

  1. OCEANIC-OCEANIC PLATE when 2 oceanic plates diverge, fractures are formed magma rises at zone of divergence to create ridge of new oceanic floor; sea-floor spreading when 2 oceanic plates diverge, mid-oceanic ridge is formed at various point along MOR, magma builds up and solidify forming undersea volcanoes; shield volcanoes when these volcanoes grow above sea level, they are known as volcanic island                     EXAMPLE           mid-atlantic ridge: north american                                                       plate & eurasian plate                                                  azores: a chain of volcanic island in                                                      north atlantic ridge !! youngest rocks are closest to middle of ridge     why?   new crust form continuously. old crust pushed further                      away from plate boundary

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DIVERGENT

  2. CONTINENTAL-CONTINENTAL PLATE when plates diverge, they are stretched, causing fractures to form; faulting when faulting occurs, tensional forces can cause a central block of land to subside between parallel faults, forming rift valley block mountains can be formed too                      EXAMPLE          east african rift valley: somalian &                                                        nubian plate boundary of african                                                           plate                                                   hutt valley, new zealand:                                                                         australian plate & pacific plate                                                   black forest, germany: eurasian                                                            plate & north american plate

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CONVERGENT

  1.OCEANIC-OCEANIC PLATE when 2 oceanic plates converge & collide, the denser oceanic plate will subduct beneath the less dense oceanic plate; subduction zone a deep oceanic trench is formed at the point of subduction the subducted ocean plate causes mantle material above it to melt, forming magma magma rises through the cracks in the crust and form volcanoes; eventually a chain/arc of island earthquake may occur due to friction created                     EXAMPLE           mariana island & mariana trench:                                                          pacific plate & phillipine plate

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CONVERGENT

  2. CONTINENTAL-CONTINENTAL PLATE 2 continental plates may collide and push against one another they resist subduction because both plates are too thick and buoyant for subduction to occur this causes plates to break and slide along fractures in the crust layers of rock on the upper part of the crust are then compressed together, they fold sideways/upwards creating fold mountains; folding                    EXAMPLE           himalayas: indian plate & eurasian                                                        plate

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CONVERGENT

  3. OCEANIC-CONTINENTAL PLATE when an oceanic plate converges with a continental plate, the denser oceanic plate subducts beneath the less dense continental plate an oceanic trench is formed at subduction zone the edges of continental plate buckles and folds, forming fold mountains at subduction zone, sinking plate causes mantle material to melt, forming magma magma rises through the cracks, giving rise to volcanic eruptions                     EXAMPLE           sunda trench: australian plate &                                                            eurasian plate

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TRANSFORM

  1. TRANSFORM plates slide past each other along transform plate boundaries this results in the formation of a transform fault as they do so, tremendous stress builds up this stress is eventually released as violent earthquake and tsunami                    EXAMPLE           san andreas fault, usa: pacific plate                                                       & north american plate                                                 anatolian fault, turkey: eurasian plate                                                   & anatolian plate  

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LANDFORMS AT PLATE BOUNDARIES

  1. DIVERGENT PLATE BOUNDARY   rift valley         -a valley formed with steep slope         -formed along faults block mountain         -a block of land with a steep slope         -when sections of crust along fault lines sink due to                           tensional force

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LANDFORMS AT PLATE BOUNDARIES

  2. CONVERGENT PLATE BOUNDARY fold mountains         -when there is increasing compressional force on 1 limb of a          fold, the rocks may buckle until a fracture forms.          -the limb may then move forward to ride over the other                   limb !! sedimentary rocks: formed from multiple layers of sediments       igneous rocks: formed when molten rocks cool and solidify       metamorphic rocks: formed when rocks are charged by high                                              temperatures/ pressure

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Caption: : syncline- v anticline-A

VOLCANOES

 DEFINITION landform formed by magma ejected from the mantle onto the earth's surface  TYPES shield volcano         -low silica, low viscosity         -gently sloping sides, wide summit         -non-explosive (gas escapes easily)         EXAMPLE     mount washington  !! flows over long distance

​​​​​​​​​​​​​stratovolcano volcano         -high silica, high viscosity         -steeper at top, gentler at base         -explosive (traps gas) ; pyroclastic flow, lahars         EXAMPLE    mount pinatubo  !!  flows over short distance + ash  ?? viscosity: stickiness of the lava/ its resistance to flow​​​​​​​

VOLCANOES

 FORMATION more magma seeps into magma chamber, amount of pressure in chamber builds up giving rise to volcanic eruption when stratovolcano erupts, pyroclasts are released; force of volcanic eruption depends on amount of pressure being built up new eruption of lava covers pyroclasts and builds up volcano lava builds up around the vent, solidifying to form a small volcanic cone; crater during formation, vent may become blocked; secondary cone develops as magma is forced to find new exit route summit of volcano may be blown off during an explosive eruption; sides of crater collapse inwards due to loss of structural support; caldera

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SHIELD VOLCANOES

formed where low silica lava ejected low silica lava less viscous and flows easily, spreading out over larger area results in gently sloping sides and broad summit less viscuos, does not trap much gas, not explosive divergent plate boudaries         EXAMPLE   mount washington, usa

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STRATOVOLCANOES

formed where high silica lava ejected high silica lava more viscous and traps heat more easily results in pressure building up as magma rises to surface, gases able to expand, causing outward explosion eruption ejects lava and pyroclasts successive erueption builds high volcano with steeper side and gentler base when pyroclasts mix with super heated gases; pyroclastic flow, 200m/sec pyroclasts mix with water; lahars, fast flowing muflow, 40m/sec         EXAMPLE     mount pinatubo, philippines, 1991, 10m tonnes                                of lava and 20m tonnes of ash                                mount merapi, indonesia

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DISTRIBUTION OF VOLCANOES

most earthquake and volcanic eruption; pacific ring of fire PROF found along convergent plate boundary volcanoes not only PROF but also other places like atlantic ocean and east africa hence, there is a close correlation between locations of plate boundaries and distribution of major active volcanoes