Topic 1- Tectonic Hazards

Question 1

Where do most earthquakes occur?

Answer 1

Along plate boundaries

Question 2

Where do the most powerful earthquakes occur?

Answer 2

At convergent or conservative boundaries.

Question 3

What are the two classifications of tectonic hazards?

Answer 3

Seismic and volcanic

Question 4

What is a tectonic hazard?

Answer 4

Any danger caused by the movement of plate tectonics, which can involve earthquakes, volcanoes and tsunamis as well as jökulhlaups.

Question 5

What are the earthquakes called that happen near the middle of plates? and what are they associated with?

Answer 5

Intra-plate earthquakes.

Ancient fault lines.

Question 6

What is the oceanic fracture zone(OFZ)?

Answer 6

A belt of activity through the oceans along the mid-ocean ridges, coming ashore in Africa, the Red Sea, the Dead Sea rift and California.

Question 7

What is the continental fracture zone(CFZ)?

Answer 7

A belt following the mountain ranges from Spain, via the Alps, to the Middle East, the Himalayas to the East Indies and then around the Pacific.

Question 8

Where are most volcanic zones found?

Answer 8

On or near to plate boundaries, depending on the margin type.

Also a strong presence on the ‘ring of fire’.

Question 9

What are volcanoes near the middle of plates called? and what are these associated with?

Answer 9

Intra-plate volcanoes(hotspots).

These are associated with upwelling or mantle plumes.

Question 10

Describe the frequency and explosiveness of volcanoes at divergent plate boundaries?

Answer 10

Very frequent. Not very explosive.

Question 11

Describe the frequency and explosiveness of volcanoes at convergent plate boundaries?

Answer 11

Not very frequent. Very explosive(high silica levels of magma).

Question 12

Give an example of an earthquake at an intra plate location

Answer 12

On the Tibetan Plateau

Crustal faults happen many thousands of kms behind the plate boundary and contribute to earthquakes such as the China (Sichuan) earthquake of 2008.

Indian plate moves towards the Eurasian plate.

Question 13

What happens at a divergent plate boundaries?

Answer 13

Where new crust is generated as the plates pull away from each other.

Question 14

What happens at convergent plate boundaries?

Answer 14

Where crust is consumed in the Earth’s interior as one plate dives under another.

Question 15

What happens at transform plate boundaries?

Answer 15

Where crust is neither produced nor destroyed as plates slide horizontally past each other.

Question 16

What are plate boundary zones?(name some zones)

Answer 16

Broad belts in which deformation is diffuse and boundaries are not well defined(these are areas such as SW USA and southern Europe)

Question 17

List a few prominent hotspot volcanoes around the world?

Answer 17

Hawaii, Galapagos, Yellowstone, Azores, Iceland, Afar.

Question 18

What is mantle plume?

Answer 18

There are two huge mantle plumes(Pacific and African); these are especially hot areas of the mantle that move upwards underneath the crust and push it up. They can cause weak points in the crust which can become hot spots.

Question 19

What are hot spots?

Answer 19

Magma from the mantle has broken through a weak point in the crust. There appear to be two types- one associated with individual upwelling from near the core-mantle boundary, and the second fro the top of large mantle plumes.

Question 20

What is the correct name for magma?

Answer 20

Superheated rock.

Question 21

Describe the process of how hot spot volcanoes form.

Answer 21

The mantle plume acts as a constant source of heat. The plume rises from the hot spot through the mantle. As it reaches the upper mantle, the asthenosphere and base of the lithosphere melt. Magma rises through weakness in the crust. Magma erupts onto the seafloor forming a seamount. Continuous eruption causes the seamount to break through the surface of the water, forming an island volcano.

Question 22

Why does volcanic activity stop at hotspot volcanoes

Answer 22

As the plate moves, the island is carried beyond the hotspot, cutting it off from the magma. This makes the volcanic activity stops. However, the mantle plume remains in a fixed location.

Question 23

Describe the formation of a hotspot volcano.

Answer 23

Hotspot volcanoes are formed when magma rises to the surface. The magma erupts through the oceanic crust. Lava builds up on the surface over time to form volcanic islands. As the oceanic crust moves over the hotspot, chains of islands develop.

Question 24

What percentage of earthquakes are found in the pacific ring of fire?

Answer 24

70%

Question 25

What percentage of earthquakes occur along plate boundaries?

Answer 25

95%

Question 26

Give some examples of quasi natural earthquakes?

Answer 26

HEP projects such as Akosombo dam, fracking in the US and UK- Lancashire, Blackpool experience crustal re-adjustment, so too Oklahoma in US.

Question 27

Give an example of a country that is experiencing more earthquakes due to global climate change

Answer 27

Iceland is experiencing more earthquakes than ever before due to isostatic rebound(uplift).

Question 28

What is the structure of the Earth(inner to outer)?

Answer 28

Inner core, Outer core, Lower mantle, Upper mantle, Asthenosphere, Lithosphere(part crust).

Question 29

What is the rough thickness of the crust( divide into oceanic and continental)?

Answer 29

Oceanic: 7km thick
Continental: 70km thick

Question 30

What is the rough the rough thickness of the mantle?

Answer 30

700-2890km deep

Question 31

What is the rough thickness of the outer core?

Answer 31

2890-5150km deep

Question 32

What is the rough thickness of the inner core?

Answer 32

5150km deep to centre

Question 33

What is the surface temperature of the the crust?

Answer 33

400˚C

Question 34

What is the temperature of the mantle

Answer 34

870˚C

Question 35

What is the temperature of the outer core?

Answer 35

4400-6100˚C

Question 36

What is the temperature of the inner core?

Answer 36

7000˚C (due to radioactive decay)

Question 37

What are the 5 tectonic based developments that have helped explained the theory of plate tectonics?

Answer 37

Earth’s structure
Continental drift
Sea-floor spreading
Paleo-magnetism
Convection currents and other movement processes

Question 38

Who developed the theory of continental drift and in what year?

Answer 38

Alfred Wegener, 1912.

Question 39

How long ago did the continent Pangaea exist?

Answer 39

300 million years ago.

Question 40

What 5 pieces of evidence did Alfred Wegener have when he published his book ‘the origin of continents and ocean’

Answer 40

The jigsaw fit of continents- South America and Africa
Geological evidence- Appalachian mountains in the NE USA which are geologically related to the Caledonian mountains of NW Scotland.
Biological evidence- such as the remains of the reptile Mesosaurus being found in southern Africa and south America( it could not have evolved identically in two such different locations).
Coal deposits- These are only formed under warm, wet climates and have been located in Antartica(Antartica must have been closer to the equator at one point and similarly with Svalbard ad the UK).
Glacial Evidence- such as from the Permo-Carboniferous glaciation(300 million years ago) found in Antartica, Africa and S.America, India and Australia suggesting they were once together.

Question 41

Who developed the theory of Sea floor spreading and in what year?

Answer 41

Harry Hess(US geologist), 1962

Question 42

How did the theory of sea-floor spreading come about what what is it in detail?

Answer 42

Harry Hess studied the age of the rocks on the Atlantic seabed and found the youngest in the middle of the ocean in Iceland and the oldest nearest the USA and Europe. This was evidence that the Atlantic sea floor was spreading outwards from the centre at approx. 5cm a year.

Oceans grow from their centres, with molten material(basalt) oozing up from the Earth’s mantle along the mid ocean ridges. This created new seafloor which then spread away from the ridge in both direction.

Question 43

What did Harry Hess believe that the area of ocean trenches were?

Answer 43

The location where ocean floor was destroyed and recycled.

Question 44

Who developed the theory of Palaeomagnetism and in what year?

Answer 44

Vine and Matthews(British geologists), 1963

Question 45

How often does the Earth’s magnetic field switch polarity?

Answer 45

Every 400,000 years

Question 46

What was the hypothesis of Palaeomagnetism?

Answer 46

When material from the mantle rises up through mid ocean ridges and cools. it preserves a record of the polarity of the Earth’s magnetic field as the magnetic iron in basaltic lava will align with the north pole when it cools.- when the polarity switches, so too will the lava’s orientation.

Question 47

What did Vine and Matthews realise from the research they conducted on their hypothesis?

Answer 47

They noticed there was a symmetrical pattern of magnetic stripes on either side of the mid ocean ridges. Aslo when the basalts of the sea floor were dated, they were found to be the same age at similar distances away from the ridge on each side and progressively older the further you move from the mid-Atlantic ridge. This confirms that the Atlantic ocean floor was created at the mid ocean ridges, the moved sideways. They published the idea in 1963 and this became the first scientific test of sea floor spreading, and a crucial development in the theory of plate tectonics.

Question 48

What does the data of palaeomagnetism suggest about the growth of the earth?

Answer 48

It suggests that the Earth would be getting bigger were it not for the earlier discovery of deep ocean trenches where ocean floor was being pulled down(subducted) or destroyed.