tectonic hazards - natural hazards Flashcards
volcanoes, earthquakes, plates
oceanic crust
heavy, thin, young, high density
continental crust
thick, old, light, low density
convection currents
hot, less dense mantle rises & cools, becoming more dense. so sinks to bottom & is heated. causing movements of plates
ridge push
at constructive margins ocean ridges form. mantle is hot & rises, pushing crust apart causing rocks to fracture & fault. molten magma pushes through cracks forcing plates to move apart. as new crustal material cools, it becomes denser & slides down, away from the ridge.
slab pull
at destructive margins dense oceanic plate sinks into mantle under influence of gravity, which pulls rest of plate along behind.
constructive margin
plates move away from each other due to convection currents dragging plates apart. ridge push contributes. upper part of mantle melts & hot magma wells up to surface, forcing plates apart. magma cools forming solid rock this can create new crust/shield volcanoes. movement + fracturing can cause earthquakes.
example of constructive margin
Mid-atlantic ridge between North American & Eurasian plates
conservative margin
plates move past in each other opp. directions/diff. speeds. friction occurs & plates become stuck. pressure builds. when released sends out energy causing earthquake. no volcanoes.
conservative margin example
San Andreas Fault
destructive margin
oceanic & continental crust move towards one another. pressure builds leading to fracturing rocks which can cause earthquakes. oceanic is forced beneath continental - subduction. sinking plate melts to form magma. pressure of magma builds & escapes through weaknesses in rock. rises as composite volcano.
destructive margin example
Nazca & South American
collision margin
2 continental plates are forced together resulting in large fold mountains. same density so crash together making folds in rock strata & some faults. when crust buckles & breaks earthquakes occur.
collision margin example
Himalayas, Mt. Everest
crust meaning
outer layer of earth
mantle meaning
layer of molten rock between core & crust
magma meaning
heat from core’s hot enough to melt rock in mantle, molten rock on surface is called lava
sea-floor spreading
when 2 oceanic plates pull apart at constructive margin, magma rises & creates new ocean floor
rift valleys
2 continental plates pull apart, narrow steep sided valley is created
shield volcano
-constructive margin
-wide base, gentle slopes
-only lava
-regular & calm eruptions
-e.g. Hekla & Surtsey, Iceland
composite volcano
-destructive margin
-tall cone, narrow base, steep sides
-alternate layers of lava + ash
-irregular, violent explosions
-e.g. Etna & Vesuvius, Italy
volcanic primary hazards (5)
-lava flows
-volcanic bombs
-gas cloud
-pyroclastic flow
-ash falls
volcanic secondary hazard (5)
-tsunami
-landslides
-glacier bursts
-lahars
-climate change
volcanic immediate effects (4)
-ppl killed & injured
-farmland & buildings destroyed
-communications damaged/disrupted
-water, gas, electricity disrupted
volcanic long-term effects
-spread of disease due to lack of clean water & broken sewers
-hospitals overwhelmed
-lack food, water, shelter & medicine
-loss income & food
-economic impact
earthquake meaning
sudden shaking of ground caused by sudden release of pressure creating seismic waves
Benefits of Mercalli scale
-more useful for aid
-specific about damage cause
-cheaper
benefits of Richter scale
-objective, accurate
-quick results
-good for comparison, prediction
-universally used
4 disadvantages of Mercalli scale
-can be disputed, subjective
-takes time/resources
-can’t be used for comparisons
-dangerous?
disadvantages of Richter scale
-ignores amount of damage caused
-needs equipment
-can be hard to understand
factors affecting earthquakes (12)
epicentre, focus, population density, building standards, prediction, geology, development, magnitude, timing, prep, location, government
epicentre meaning
point on earth’s surface vertically above focus
focus meaning
origin of earthquake within crust
immediate responses of earthquakes (6)
-evacuation
-volunteers search for survivors
-rescue teams deployed
-medical tents set up
-money donated to buy supplies
-tents given out
long-term responses of earthquakes (6)
-building regulations improved
-investment focussed on rebuilding
-homes rebuilt
-ppl move permanently
-new jobs in construction
-schools/hospitals rebuilt
monitoring + preparing for earthquakes (5)
-use radon detection devices measure radon gas in soil & groundwater
-sensitive seismometers measure tremors/foreshocks
-locations & times mapped to see patterns
-unusual animal behaviour
-phones have GPS receivers & accelerators that detect ground motion
protection for earthquakes + example
(3)
-rubber shock absorbers = prevent shaking causing collapse
-rolling weights on roof =counteract shockwaves
-reinforced lift shafts with tensioned cables = saves any trapped inside
-e.g. Transamerica building
planning for earthquakes
(5)
-fasten down furniture
-know how to turn off gas, water, electricity
-prepare emergency supplies
-create plans for evacuation
-educate - earthquake drills
monitoring & prediction of volcanoes (4)
-satellites & tiltmeters monitor ground deformation & bulges on v
-seismometers measure small earthquakes & tremors
-thermal sensors detect temp changes on surface
-gas-trapping bottles measure radon & sulfur gases released
protection for volcanoes (4)
-difficult bc buildings don’t withstand lava, lahars, ash
-dig trenches
-dump concrete blocks in lava flows (etna)
-artificial barriers (hawaii)
planning for volcanoes (4)
-risk maps, evacuate
-exclusions zones
-educating
-emergency shelters
