Tectonics EQ1

Question 1

What are the layers of the earth?

Answer 1

Core
Mantle
Asthenosphere
Lithosphere

Question 2

Describe the core

Answer 2

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

Question 3

Describe the mantle

Answer 3

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

Question 4

Describe the asthenosphere

Answer 4

Part of the mantle
Semi-molten
Below the lithosphere

Question 5

Describe the lithosphere

Answer 5

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

Question 6

What is a convergent plate margin

Answer 6

When two plates move towards each other

Oceanic plate slides beneath the continental plate

Question 7

Describe what happens at a convergent margin

Answer 7

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

Question 8

What is a conservative plate margin

Answer 8

When two plates slide past each other horizontally

Question 9

Describe what happens at a conservative plate margin

Answer 9

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

Question 10

What is a divergent plate margin

Answer 10

When two plates move away from each other

Question 11

Describe what happens at a divergent plate margin

Answer 11

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

Question 12

What features does an oceanic plate have

Answer 12

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

Question 13

What features does a continental plate have

Answer 13

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

Question 14

Define a hazard

Answer 14

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

Question 15

How are hazards distributed

Answer 15

Unevenly

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

Question 16

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

Answer 16

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

Question 17

Describe a hotspot

Answer 17

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

Question 18

Describe intra-plate volcanoes

Answer 18

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

Question 19

Describe intra-plate earthquakes

Answer 19

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

Question 20

Define gravitational sliding

Answer 20

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

Question 21

What is sea floor spreading

Answer 21

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

Question 22

Describe Holmes’ hypothesis

Answer 22

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

Question 23

Describe slab pull

Answer 23

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

Question 24

Describe Wegener’s continental drift hypothesis

Answer 24

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

Question 25

What is the focus

Answer 25

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

Question 26

What is the epicentre

Answer 26

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

Question 27

What are seismic waves

Answer 27

When energy is released from the focus in shock waves | Most damage occurs where the shock waves are strongest (closest to epicentre)

Question 28

What causes earthquakes

Answer 28

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

Question 29

What is a deep-focus earthquake

Answer 29

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

Question 30

What is a shallow focus earthquake

Answer 30

Those where the focus is 0-70km under earths surface | Generally more damaging as waves don’t have as far to travel

Question 31

What is an underwater earthquake

Answer 31

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

Question 32

What are P-waves

Answer 32

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

Question 33

What are L-waves

Answer 33

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

Question 34

What are S-waves

Answer 34

Secondary waves | Produced by some earthquakes that make ground shake violently

Question 35

What are 2 common primary hazards of earthquakes

Answer 35

Ground shaking | Crystal fracturing

Question 36

Describe the duration and severity of ground shaking

Answer 36

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

Question 37

Describe crustal fracturing

Answer 37

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

Question 38

What are 3 common secondary hazards of earthquakes

Answer 38

Landslides Liquefaction Tsunamis

Question 39

What is liquefaction

Answer 39

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

Question 40

Name 4 primary hazards of volcanoes

Answer 40

Ash falls Volcanic gases Pyroclastic flows Lava flows

Question 41

Describe ash falls

Answer 41

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

Question 42

Describe volcanic gas

Answer 42

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

Question 43

Describe pyroclastic flows

Answer 43

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

Question 44

Describe lava flows

Answer 44

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

Question 45

Name 2 secondary hazards of volcanoes

Answer 45

Lahars | Jökulhlaup

Question 46

Describe a lahar

Answer 46

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

Question 47

Describe jökulhlaups

Answer 47

Flooding that happens when glaciers or ice caps melt | Originates from Iceland where sun glacial outburst floods happen

Question 48

What causes a tsunamis

Answer 48

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

Question 49

What are the characteristics of tsunamis

Answer 49

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

Question 50

What is the Benioff Zone

Answer 50

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