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geography > 1.1 - Locations at risk from tectonic hazards > Flashcards

1.1 - Locations at risk from tectonic hazards Flashcards

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1
Q

What is a hazard

A

potential threat to human life and property

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2
Q

What is the global distribution of earthquakes?

A

The main earthquake zones are often found in clusters along plate boundaries - 90% of earthquakes are found at plate boundaries

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3
Q

What is the global distribution of volcanoes?

A

-plate margins

-pacific ring of fire

-hotspot

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4
Q

What is the global distribution of tsunamis?

A

Most tsunamis are generated along subduction zones, and 90% occur around the Pacific Basin

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5
Q

What is the oceanic fracture zone (OFZ)

A

belt of activity through the ocean and along the mid-ocean ridges through Africa, Red Sea, Dead Sea

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6
Q

What is the continental fracture zone (CFZ)

A

belt of activity along the mountain ranges from spain through to alps to middle east and himalayas

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7
Q

What happens at divergent (constructive) plate boundaries?

A

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

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8
Q

What happens at convergent (destructive) plate boundaries? (oceanic-continental)

A

-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

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9
Q

What happens at conservative plate boundaries?

A

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

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10
Q

What is a volcanic hotspot, and how do volcanoes form here?

A

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)

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11
Q

Name the 2 different crusts and their properties

A

Oceanic crust - thin, composed primarily of basalt but denser

Continental crust - thicker, composed primarily of granite and less dense

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12
Q

How do convection currents drive plate movement?

A

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

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13
Q

How does slab pull drive plate movement?

A

when older, denser plates sink into mantle, pulling newer, less dense sections of plate along

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14
Q

How does ridge push drive plate movement?

A

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

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15
Q

What is sea floor spreading?

A

The continuous input of magma forming a mid ocean ridge, for example the Mid-Atlantic Ridge

-occurs at cosntructive plate boundaries

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16
Q

What causes an earthquake

A

-> 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

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17
Q

Give an example of a vlocanic hotspot

A

hawaii hotspot

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18
Q

What is used to measure groundshaking caused by seismic waves

A

seismometer

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19
Q

Name the 3 types of seismic waves

A

-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

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20
Q

Name 2 secondary hazards of earthquakes

A

soil liquefaction -> can cause buildings to settle, tilt, collapse

landslides -> can pick up trees, cars -> damage, death

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21
Q

What is soil liquefaction

A

when water-saturated material loses strength -> behaves like a liquid

22
Q

What are landslides

A

where slopes weaken & fail

23
Q

How are tsunamis generated?

A

Series of waves caused by sea bed displacement, often caused by submarine earthquakes at subduction zones leading to the displacement of a water column.

24
Q

What are some of the primary hazards associated with volcanic eruptions?

A

Pyroclastic flows, tephra, lava flows, volcanic gases, ash falls

25
Q

What are some of the secondary hazards associated with volcanic eruptions?

A

Lahars

Jokulhlaups

26
Q

What are lahars

A

Volcanic mudflows generally composed of fine sand and silt material

27
Q

What are jokulhlaups?

A

floods caused by volcanic eruptions beneath glaciers

28
Q

Name 3 properties of tsunamis

A

-long wavelength
-low amplitude
-fast velocities

29
Q

What are pyroclastic flows

A

frothing of magma at vent -> produce bubbles that burst -> hot & poisonous gas exploding

-flow down the flanks of volcanoes

30
Q

What is tephra

A

(ash fall)
rock fragments ejected into air

-> accumulates on roofs -> fires, collapsing

-> kills vegetation

31
Q

What are lava flows

A

flows of molten rock

-fast moving

32
Q

What are volcanic gases

A

mixed gases emitted during explosive eruptions

-inc carbon monoxide

33
Q

What is the hypocentre of an earthquake

A

point of origin where pressure is released inside earth

34
Q

Name 3 factors which effect how impactful tsunamis are

A

-duration of event

-degree of coastal protection

-density of pop

-timing of event - night/ day

35
Q

What is the Benioff zone?

A

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

36
Q

Explain the 8 steps on how an tsunami forms

A

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

37
Q

What are subduction zones

A

where 2 plates are moving together

-thinner, more dense oceanic plate descends beneath continental plate

38
Q

What is paleomagnetism?

A

resuts from magma locking in the earths magnetic

39
Q

Explain the plate tectonics theory

A

-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

40
Q

What is a volcano

A

landform that develops around a weakness in the earth’s crust from which molten magma, volcanic rock -> ejected into air

41
Q

Name the 3 types of plate boundary

A

-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

42
Q

Describe constructive (divergent) plate movement and the earthquakes it produces

A

-where plates move away from each other

-oceanic crust is created

43
Q

What 2 landforms are associated with constructive plate boundaries

A

-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

44
Q

Give a 3 step brief description of what occurs at constructive margins

A

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

45
Q

Give a 3 step brief description of what occurs at destructive margins

A

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

46
Q

Name the 5 components of the Earth’s structure

A

-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

47
Q

Name a primary hazard caused by earthquakes

A

crustal fracturing - buckling, fracturing of crust due to waves

48
Q

What are subduction zones

A

areas where 2 plates move together with oceanic subducting beneath continental

49
Q

What is a locked fault

A

fault that isn’t slipping due to frictional resistance on the fault being greater than the stress across the fault

50
Q

Meaning of magnitude in terms of earthquake

A

amount of movement/ displacement in the fault which is a measure of energy release

51
Q

What is an epicentre

A

point where earthquake originates

geography (55 decks)

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