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why are some locations more at risk to tectonic hazards - Coggle Diagram
why are some locations more at risk to tectonic hazards
tectonics
-natural event: volcanic eruption, earthquake - the event itself
-hazard: becomes a hazard when it becomes a risk to people
-disaster: when the hazard has an significant affect on the population
-Haiti eq 2010:
-mag 7
-more damage due to it being a poorer and less developed area
-250,000 deaths
-Japan eq+tsunami 2011:
-mag 9
-more development so more management of hazard so less deaths
-20,000 deaths (230,000 less)
-a mag 9 is the biggest eq ever recorded off the coast of Japan
-a mag 9 releases 1000x more energy than a mag 7 eq
-from a mag 7 to mag 8 it releases 32x as much energy
-deggs disaster model:
-the worse the natural hazard and the more vulnerable the population = worse the disaster
plate tectonics
-theory of plate tectonics published in 1962 based on earlier discoveries and a better understanding of the structure of the earth
-scientists interpret the way in which seismic waves pass through the planet to judge the structure of inner earth
-continental crust:
-solid magma
-granite
-less dense - 2.5 g/cm cubed
-thicker - 70 km
-oceanic crust:
-solid magma
-basalt
-denser - 2.9 g/cm cubed
-thinner - 6 km
-formed quicker as cold water cools the magma
-the lithosphere: includes crust and solid mantle stuck to continental crust
-plastic asthenosphere:
-deeper and hotter than lithosphere
-semi molten mantle (plastic like)
-tectonic plates:
-7 major slabs on the lithosphere
-plates can be continental and/or oceanic
-float on asthenosphere magma
-move 1-15 cm/year
plate tectonic theory
-evidence for plate tectonics:
-in 1912 Alfred Wegener suggested the idea of continental drift, but at the time couldn't explain how it happened
-new evidence led to the theory of plate tectonics in 1968 and the understanding that there were tectonic plates that had been moving slowly over the earths surface for millions of years (continental drift)
-palaeomagnetism: provides evidence for plate divergence and seafloor spreading
-the study of palaeomagnetism of rocks in the ocean floor show a symmetrical pattern in the age of rocks on either side of the mid Atlantic ridge and also symmetry in the changing polarity of iron in the rocks
-the ocean floor is getting wider at 3cm/year
-plate movement:
1- magma rises at an plate boundry
2- it solidifies pushing existing rock apart
3- process repeats creating symmetrical patterns
-plate movement is driven by mantle convection:
-hot magma rises through the mantle, as it rises it cools and spreads out becoming dense crust, it then sinks back into the core becoming magma
-magma moves in convection currents in the asthenosphere causing friction that moves the lithosphere
tectonic plate boundries
-constructive or divergent
-destructive or convergent
-conservative or transform
-magma: molten rock below earths surface
-lava: magma that's erupted above earths surface
-constructive plate boundary:
-magma rises to fill rift left by diverging plate, construct and create new plate margins
-these form mid-Atlantic ridges (submarine mountain ranges)
-mid-Atlantic ridge: mid ocean ridge at constructive plate boundary
-Iceland: where mid-Atlantic ridge volcanoes rise above sea level
-oceanic and continental destructive boundary:
-subducting plate margin destroyed by melting
-the Andes in S America: fold mountains and volcano are at destructive boundary
-oceanic and oceanic destructive boundary:
-the Antilles (Caribbean): a volcanic island at a destructive plate boundary
-continental and continental destructive boundary:
-Himalaya (Asia): fold mountains at a destructive boundary
-conservative boundary:
-plate margins not created or destroyed
-San Andreas fault (California): Pacific and N American plate
-slab pull:
-oceanic plates form at mid-ocean ridges
-as they diverge they cool, become denser and subduct
-this pulls down the rest of the plate melting into magma
-seafloor spreading:
-magma rises at rifts and erupts as lava and forms large volcanoes
-oceanic plates pulled apart by weight of mid-oceanic ridge - ridge push
-oceans grow as plates diverge