1.1 - Locations at risk from tectonic hazards Flashcards
What is a hazard
potential threat to human life and property
What is the global distribution of earthquakes?
The main earthquake zones are often found in clusters along plate boundaries - 90% of earthquakes are found at plate boundaries
What is the global distribution of volcanoes?
-plate margins
-pacific ring of fire
-hotspot
What is the global distribution of tsunamis?
Most tsunamis are generated along subduction zones, and 90% occur around the Pacific Basin
What is the oceanic fracture zone (OFZ)
belt of activity through the ocean and along the mid-ocean ridges through Africa, Red Sea, Dead Sea
What is the continental fracture zone (CFZ)
belt of activity along the mountain ranges from spain through to alps to middle east and himalayas
What happens at divergent (constructive) plate boundaries?
Two plates are moving away from each other (can be continental or oceanic), earths crust pulled apart -> rising hot magma onto surface -> forms new crust
-oceanic-oceanic -> rising convection currents brings magma to surface -> small eruption -> basaltic volcanoes, minor earthquakes
-e.g. mid-atlantic ridge - iceland
-continental-continental -> mantle plume splits continental plate -> creatinf new ocean basin
-e.g. african rift valley/ red sea
What happens at convergent (destructive) plate boundaries? (oceanic-continental)
-where 2 plates move together
-oceanic - oceanic -> oceanic plate is subducted beneath another
-> frequent earthquakes
-> curving (arc) chain of volcanic islands
-e.g. Aleutian islands - alaska
-continental - continetal -> collision of 2 continental plates -> mountain belt forms from crumpled crust
->magma generates at depth -> major earthquakes
-> volcanic eruptions
-e.g. himalayas - indo-australian and eurasian plates
-oceanic- continental -> denser oceanic plate subducts beneath continental plate
-> volcanic mountain range
->frequent large earthquakes
-e.g. Andean Mountains
What happens at conservative plate boundaries?
two plates are sliding past each other along transform faults
causes a build up of friction -> they drag against each other
->earthquakes occur
-> no volcanoes
What is a volcanic hotspot, and how do volcanoes form here?
where magma rises up through crust
-melts through the lithosphere, through the cracks -> active volcanoes
As the tectonic plate moves over the hotspot like a conveyer belt, a series chain of volcanoes forms (e.g. Hawaii)
Name the 2 different crusts and their properties
Oceanic crust - thin, composed primarily of basalt but denser
Continental crust - thicker, composed primarily of granite and less dense
How do convection currents drive plate movement?
Heat from Earth’s core rises within the mantle -> drives rocks ^.
these rocks drag along the tectonic plates, slowly moving them before sinking as they lose heat from the Earth’s core. This creates a convection current cell, heat constantly rising and falling to power plate movement
How does slab pull drive plate movement?
when older, denser plates sink into mantle, pulling newer, less dense sections of plate along
How does ridge push drive plate movement?
magma ^ as plates move apart -> cools forming new plate material
as it cools it becomes denser & slides down away from the ridge causing other plates to move away from each other
What is sea floor spreading?
The continuous input of magma forming a mid ocean ridge, for example the Mid-Atlantic Ridge
-occurs at cosntructive plate boundaries
What causes an earthquake
-> as 2 plates move past each other they stick
-> earth’s crust has faults within it
-> as tectonic strain builds up -> ^ stress
-> when pressure exceeds strength of the fault -> rock fractures
-> produces sudden release of energy -> creating seismic waves
-> brittle crust either side of fracture rebounds -> groundshaking
Give an example of a vlocanic hotspot
hawaii hotspot
What is used to measure groundshaking caused by seismic waves
seismometer
Name the 3 types of seismic waves
-primary/ p waves -> come 1st -> vibrations caused by compression - 8km/s
-secondary/ S waves -> vibrate at right angles - 4km/s
-love/ L waves -> surface waves of vibration
Name 2 secondary hazards of earthquakes
soil liquefaction -> can cause buildings to settle, tilt, collapse
landslides -> can pick up trees, cars -> damage, death
What is soil liquefaction
when water-saturated material loses strength -> behaves like a liquid
What are landslides
where slopes weaken & fail
How are tsunamis generated?
Series of waves caused by sea bed displacement, often caused by submarine earthquakes at subduction zones leading to the displacement of a water column.
What are some of the primary hazards associated with volcanic eruptions?
Pyroclastic flows, tephra, lava flows, volcanic gases, ash falls
What are some of the secondary hazards associated with volcanic eruptions?
Lahars
Jokulhlaups
What are lahars
Volcanic mudflows generally composed of fine sand and silt material
What are jokulhlaups?
floods caused by volcanic eruptions beneath glaciers
Name 3 properties of tsunamis
-long wavelength
-low amplitude
-fast velocities
What are pyroclastic flows
frothing of magma at vent -> produce bubbles that burst -> hot & poisonous gas exploding
-flow down the flanks of volcanoes
What is tephra
(ash fall)
rock fragments ejected into air
-> accumulates on roofs -> fires, collapsing
-> kills vegetation
What are lava flows
flows of molten rock
-fast moving
What are volcanic gases
mixed gases emitted during explosive eruptions
-inc carbon monoxide
What is the hypocentre of an earthquake
point of origin where pressure is released inside earth
Name 3 factors which effect how impactful tsunamis are
-duration of event
-degree of coastal protection
-density of pop
-timing of event - night/ day
What is the Benioff zone?
boundary between an oceanic plate undergoing subduction & an overriding continetal plate
-its a sloping plane -> stresses are built up as cold oceanic plate sinks into hot mantle
Explain the 8 steps on how an tsunami forms
1- oceanic plate slides beneath continental plate
2- this causes rock to fracture -> earthquake
3- pushes sea upwards
4- causes widening circle of waves
5- these waves ^ energy & speed
What are subduction zones
where 2 plates are moving together
-thinner, more dense oceanic plate descends beneath continental plate
What is paleomagnetism?
resuts from magma locking in the earths magnetic
Explain the plate tectonics theory
-theory that earth’s crust consists of 2 plates ->
-thin crust underlying ocean basins
-thicker crust underlying the continents
-low density of continental crust allows it to ‘float’ higher density mantle below
-heat from earths molten core ^ within mantle -> convection currents created -> moving tectonic plates
What is a volcano
landform that develops around a weakness in the earth’s crust from which molten magma, volcanic rock -> ejected into air
Name the 3 types of plate boundary
-divergent (constructive) -> where plates move away from eachother
-low magnitude & submarine earthquakes occur
-convergent (destructive) -> where plates move towards eachother
-collision locations -> plate material melts into mantle -> earthquakes, volcanoes
-conservative -> plates move against ecah other
-sites of extensive shallow focus earthquakes
Describe constructive (divergent) plate movement and the earthquakes it produces
-where plates move away from each other
-oceanic crust is created
What 2 landforms are associated with constructive plate boundaries
-ocean ridges -> underwater mountain range (e.g mid-atlantic ridge iceland) - where eurasian & north atlantic plate are moving apart under atlantic ocean
-rift valleys - > lowland region between mountains (e.g. east african rift valley) where african plate is tearing itself apart
Give a 3 step brief description of what occurs at constructive margins
plates move away from each other
tensional forces open cracks & faults between plates -> creates pathway -> magma rises towards the surface & erupts
->shallow earthquakes
-> small volcanic eruptions
Give a 3 step brief description of what occurs at destructive margins
plates move towards each other
cold, dense oceanic plate = subducted beneath less dense continental plate -> density of oceanic plate pulls istelf into mantle -> forming magma
magma rises up through weaknesses in rock -> volcano
-> earthquakes
Name the 5 components of the Earth’s structure
-crust - continental, oceanic
-lithosphere - contains crust, upper part of mantle
-asthenosphere - upper part of mantle where convection occurs
-mantle - molten rock with high temp
-upper mantle -> cool, brittle rocks
-lower mantle -> hot, plastic rocks
-outer core - liquid layer
-inner core - solid layer
Name a primary hazard caused by earthquakes
crustal fracturing - buckling, fracturing of crust due to waves
What are subduction zones
areas where 2 plates move together with oceanic subducting beneath continental
What is a locked fault
fault that isn’t slipping due to frictional resistance on the fault being greater than the stress across the fault
Meaning of magnitude in terms of earthquake
amount of movement/ displacement in the fault which is a measure of energy release
What is an epicentre
point where earthquake originates
