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Geography > Tectonics EQ1 > Flashcards

Tectonics EQ1 Flashcards

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1
Q

What are the layers of the earth?

A

Core
Mantle
Asthenosphere
Lithosphere

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2
Q

Describe the core

A

Central part of the earth
Made up of inner and outer core
Inner core is solid, outer core is liquid
Inner and outer core made from iron and nickel
Core is a source of radioactive heat

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3
Q

Describe the mantle

A

Semi-molten body of rock between the earths crust and its core

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4
Q

Describe the asthenosphere

A

Part of the mantle
Semi-molten
Below the lithosphere

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5
Q

Describe the lithosphere

A

The crust and upper mantle which form the tectonic plates
80-90km thick
Crust changes in thickness under oceans and continents: 6-10km thick under oceans, 30-40km under continents

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6
Q

What is a convergent plate margin

A

When two plates move towards each other

Oceanic plate slides beneath the continental plate

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7
Q

Describe what happens at a convergent margin

A

Crust is destroyed at oceanic plate subducts under continental at subduction zone
Rock catches against each other
Pressure between plates builds until plates can’t take stress
Plates slip past each, which can cause plates to move resulting in ground shaking

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8
Q

What is a conservative plate margin

A

When two plates slide past each other horizontally

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9
Q

Describe what happens at a conservative plate margin

A

Crust is neither produced nor destroyed
Plates catch and snag against each other
Friction and pressure builds until plates can’t take stress
Plates slip past each other which can cause both plates to move = ground shaking

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10
Q

What is a divergent plate margin

A

When two plates move away from each other

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11
Q

Describe what happens at a divergent plate margin

A

Convection currents diverge and cause a gap between plates
Magma rises up to fill the gap
New crust is generated as plates pull away from each other

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12
Q

What features does an oceanic plate have

A

High-density materials
Made of basaltic rock
Only 7-10km thick
Subduct under other plates

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13
Q

What features does a continental plate have

A

Thicker than oceanic (25-75km)
Less dense than oceanic
Made of granitic rock
Do not subduct

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14
Q

Define a hazard

A

A hazard is a natural/geophysical event that has the potential to threaten both life and infrastructure

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15
Q

How are hazards distributed

A

Unevenly

Some areas are at high risk and some are at low risk

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16
Q

Where do tectonic hazards (volcanoes, earthquakes, tsunamis) occur

A

At specific points that are usually associated with tectonic plate margins
Earthquakes also occur where the Indo-Australian plate collides with the Eurasian plate

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17
Q

Describe a hotspot

A

Where there is a hot mass of rising heat under a weakness in a plate
Magma rises to the surface through this weakness
Hawaiian islands formed as a result of a mid-Pacific hotspot

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18
Q

Describe intra-plate volcanoes

A

Mantle plumes rise towards the surface generating basaltic volcanoes
The plume remains stationary, although plate above moves over it
Continuing plate movement over time produces a chain of volcanic islands

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19
Q

Describe intra-plate earthquakes

A

Earthquakes can happen in mid-plate settings, usually associated ancient fault lines being re-activated by tectonic stresses
Zones of weaknesses are created as plates move and stress increases

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20
Q

Define gravitational sliding

A

Elevated altitudes of oceanic crust at ridges at divergent plate boundaries
Create a slope down which oceanic plate slides

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21
Q

What is sea floor spreading

A

Paleomagnetic signals from past reversals of the earths magnetic field prove that new crust is created by the process of sea floor spreading at mid-ocean ridges

22
Q

Describe Holmes’ hypothesis

A

Said the earths internal radioactive heat was the driving force of convection currents in the mantle that could move tectonic plates

23
Q

Describe slab pull

A

At convergent boundaries, ocean floor is dragged down by a downward gravitational force beneath the adjoining continental crust

24
Q

Describe Wegener’s continental drift hypothesis

A

Said that our now separate continents had once been joined together as supercontinents
Pangea

25
Q

What is the focus

A

Where the pressure is released underground and where the energy radiates out from
Place with the strongest waves that cause the most damage

26
Q

What is the epicentre

A

The point directly above the centre of the earthquake on the earth’s surface

27
Q

What are seismic waves

A

When energy is released from the focus in shock waves

Most damage occurs where the shock waves are strongest (closest to epicentre)

28
Q

What causes earthquakes

A

Release of built up stress
Plates are always moving so tensions build up between rocks
Stress can suddenly be released when strain overcomes elasticity of the rock
Energy is transferred to surface vertically then outwards from epicentre
Energy transferred through seismic waves makes ground shake

29
Q

What is a deep-focus earthquake

A

Those where the focus is 70-700km under the earths surface
Caused by previously subducted crust moving towards the core, heating up or decomposing
Generally less damaging as shock waves travel further so cause less shaking at surface

30
Q

What is a shallow focus earthquake

A

Those where the focus is 0-70km under earths surface

Generally more damaging as waves don’t have as far to travel

31
Q

What is an underwater earthquake

A

Move the seabed, which causes water to get displaced - can cause tsunamis
Can be shall or deep focus
Deeper the focus, bigger the tsunami
Waves travel fast in deep water so tsunamis strike shores with little warning

32
Q

What are P-waves

A

Primary waves
Produced when tectonic stress energy is released
Fastest waves but cause the least damage

33
Q

What are L-waves

A

Love waves
Create significant damage, including crustal fracturing
Only travel across the surface and have a large amplitude

34
Q

What are S-waves

A

Secondary waves

Produced by some earthquakes that make ground shake violently

35
Q

What are 2 common primary hazards of earthquakes

A

Ground shaking

Crystal fracturing

36
Q

Describe the duration and severity of ground shaking

A

Can range in duration and severity based on magnitude of earthquake and distance from epicentre

37
Q

Describe crustal fracturing

A

Earth can visibly separate and deep fissures in the ground can be created

38
Q

What are 3 common secondary hazards of earthquakes

A

Landslides
Liquefaction
Tsunamis

39
Q

What is liquefaction

A

When earthquakes compact loose sediments of silts, sand and gravel that are waterlogged
Compact ground forces water to rise to the surface and damage buildings and infrastructure

40
Q

Name 4 primary hazards of volcanoes

A

Ash falls
Volcanic gases
Pyroclastic flows
Lava flows

41
Q

Describe ash falls

A

Also known as tephra
Solid material of varying grain size ejected into the atmosphere
Buildings often collapse under the weight
Air becomes thick and is difficult to breathe in and can cause respiratory problems
E.g. 2010 eruption of Mount Merapi in Indonesia

42
Q

Describe volcanic gas

A

Can be poisonous e.g. carbon dioxide, carbon monoxide, sulphur dioxide
E.g. 1986 eruption of Lake Nyos, Cameroon

43
Q

Describe pyroclastic flows

A

Very hot (800°C), have a high velocity and are a mixture of gases and tephra
Can destroy everything in their paths
E.g. AD79 eruption of Mount Vesuvius, 1980 eruption of Mount St. Helens

44
Q

Describe lava flows

A

Not usually a major threat when they are molten lava as slow moving
Create extensive areas of solidified lava
E.g. Hawaii and Southwest Iceland

45
Q

Name 2 secondary hazards of volcanoes

A

Lahars

Jökulhlaup

46
Q

Describe a lahar

A

Fast mudflows that happen when rain mobilises deposits of volcanic ash
E.g. 1985 Armero tragedy took place when Nevado del Ruiz volcano erupted in Colombia, four lahars came towards town and around 20,000 people died

47
Q

Describe jökulhlaups

A

Flooding that happens when glaciers or ice caps melt

Originates from Iceland where sun glacial outburst floods happen

48
Q

What causes a tsunamis

A

Most generated by submarine earthquakes at subduction zones
Sea bed is displaced vertically which displaced a large volume of water in the ocean column which moves outwards from the point of displacement

49
Q

What are the characteristics of tsunamis

A

Long wavelength at sea - measured between 2 identical points of a wave, often over 100km long
Short amplitude at sea - usually about 1m high and barely noticeable, height increases to over 25m when reach land
Velocity - move quickly and reach speeds of 700kph in dee water
Drawback - localised drop in sea level
Wave-train - way a tsunami hits a coastline is like a series of waves

50
Q

What is the Benioff Zone

A

Area where friction is created between colliding tectonic plates, resulting in intermediate and deep earthquakes

Geography (17 decks)

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