Plate Tectonics

Question 1

Structure of the earth

Answer 1

Crust: Relatively thin layer of solid rocks around the outside of the earth
Mantle: A layer of melted rock 2900km beneath the crust. Very hot and main rock type is peridotite
Outer core: A layer of molten rock 2900-5000 km below the crust. Average temps of 3000 c and an iron/nickel composition
Inner core: Centre of the earth

Question 2

Major plates

Answer 2

The Pacific, Eurasian, African, American, Indo Australian, Nazca plate, Antarctic plate

Question 3

Plates

Answer 3

Plates are sections of very thin, they float like rafts on the semi-molten material that makes up the Earth’s mantle. They move on top of the mantle by a series of heat/convectional currents. Movement is small at less that 1cm per year, but can result in eruptions/ earthquakes

Question 4

Destructive plate

Answer 4

Happens when Oceanic and continental plates move together. Oceanic plate is denser and is forced down into the mantel (below continental). It melts and is released as magma (volcano). Continental plate is forced uo and earthquakes occur due to the movement of the plates e.g Monsterrat

Question 5

Constructive plate

Answer 5

New crust forms in undersea valleys in mid-ocean. Oceanic plates move apart causing magma to rise up as a volcanic eruption and one cooled, new land is formed. New crust gradually pushes the older crust sideways and away from the ridge. A mid-ocean ridge. Minor earthquakes occur e.g Mid Atlantic ridge

Question 6

Conservative plate

Answer 6

Two plates move past one another. Pressure builds up as the plates move causing a massive earthquake. No crust is created or destroyed and no volcanic eruptions occur e.g Haiti earthquake

Question 7

Collision plate

Answer 7

Continental plates converge (move together). They are pushed up to form a fold mountain (e.g Himalayas). Eruption occurs and sometimes violent earthquake (Nepal 2015)

Question 8

Divergent plate boundary

Answer 8

Plates move apart; earthquakes and magma are common

Question 9

Convergent plate boundary

Answer 9

Oceanic crust is often forced down into mantle where it begins to melt. Magma rises into and through the other plate, solidifying into granite. So continental crust is created and oceanic crust is destroyed

Question 10

Transform plate boundary

Answer 10

Two plates slide past each other (e.g San Andreas fault zone)

Question 11

Volcanoes form

Answer 11

Volcanoes are formed when magma from within the Earth’s upper mantle works its way up to the surface. AT the surface, it erupts to form lava flows and ash deposits. Over time, it will get bigger and bigger

Question 12

Volcanic hotspots

Answer 12

Hotspots are areas in the lithosphere (crust/ upper mantel) that are underlain by hot magma. This heat causes partial melting of the lithosphere, eventually leading to volcanic activity. Hawaiian Islands are a classic example of a volcanic grouping formed over one hot spot

Question 13

Active volcano

Answer 13

If a volcano has erupted recently

Question 14

Dormant volcano

Answer 14

If it has erupted in the past 2000 years

Question 15

Extinct volcano

Answer 15

If it hasn’t erupted for many thousands/ millions of years

Question 16

Shield volcano

Answer 16

These volcanoes have runny lave (non vicious) because of this they don’t have an explosive eruption. Lava spreads quickly across the landscape. Each eruption adds a new layer or rock built on the previous. Eventually, a wide dome of rock is built. Looks like a curved Shiel and slopes are very gentle. Hawaiian islands are a chain of shield volcanoes

Question 17

Composite volcano

Answer 17

Most common type of volcano. Classic shape. They are formed by hardened layers of lava and ash from successive eruptions. The lava is vicious (therefore thicker than Shiel volcano). This lava cools and hardens before spreading very far though and therefore they are steep sided. The eruptions tend to be very violent, capable of producing deadly pyroclastic flows. Chances peak, Monsterrat is an example of one

Question 18

Features of volcano

Answer 18

Magma chamber (bottom), cone (shape), vent (vent of lava going upwards), crater (where lava comes out), lava (liquid coming out), ash (cloud above)

Question 19

Case study: volcanic example in an LEDC

Answer 19

Monsterrat
Date: July 1995
Eruption lasted: 5 years
Chances peak volcano had been dormant for 20 years. Emergency plans were to evacuate people to nearby islands or Britain. Killed 23 people. Destroyed a lot of homes and farms. Lots of jobs lost. pyroclastic flow covered large areas of island. Located on a destructive plate boundary (North American plate moves towards Caribbean plate), North American plate is denser so it is forced into mantle. Molten rock is lighter than surrounding rock so it rises through the cracks towards the surface. Ends up producing andesitic lava (strato volcano) and lava is so thick it created a dome on the side of chances peak. Dome suffered serious collapse in 1997 and led to ash fall and pyroclastic flows engulfing a lot of the south of the island.
Effects:
landscapes changed, animals like cows are now feral as they were set free, mountain chicken frogs’ habitats destroyed, gases released, coral reefs covered in ash, business decline, economy damaged, Plymouth destroyed, less housing

Question 20

Prediction

Answer 20

• lasers to detect swelling of volcano
• chemical sensors to measure increase in sulphur levels
• seismometers to detect the large number of earthquakes that occur due to the magma rising up
• ultrasound can monitor low frequency waves within the magma
• gas sampling

Question 21

prevention

Answer 21

• have an evacuation plan

- nobody allowed to live in risky zones

Question 22

Case study: Why live near a volcano?

Answer 22

Monsterrat

• fertile land for farming-> jobs
• nice landscapes
• volcanic activity always monitored so it’s not a really negative factor
• tourims
• geothermal energy can be harnessed
• minerals are contained in lava, e.g diamonds can be mined to make money

Question 23

Earthquakes

Answer 23

An earthquake is the shaking and vibration of the crust due to movement of the Earth’s plates

Question 24

The focus

Answer 24

The point inside the Earth’s crust where the energy is released

Question 25

Epicentre

Answer 25

The surface point directly above the focus and is where the effects of the earthquake may be felt most strongly

Question 26

How are earthquakes measured

Answer 26

an earthquake is measured using a Richter scale

Question 27

Case study of an earthquake

Answer 27

Haiti

• is part of a large Caribbean island called Hispaniola. The Dominican Republic is located to the East of Haiti.
• Haiti is right on the boundary of the Caribbean and North American plates. There was a slippage along a conservative plate boundary that runs through Haiti. Friction between plates built up tension which was released in an earthquake.
• A magnitude of 7 earthquake. Port au Prince suffered the most, the capital, as that is where the epicentre is located.
• over 200,000 deaths, 1 million made homeless, several hospitals collapsed, business were effected, economic decline, buildings fell
• Very little amount of earthquake proof buildings, buildings poorly built, very few resources to rescue
• Dominican Republic provided emergency help and supplies, medical teams and camps, money was pledged to help rebuild, shelter camps, schools rebuilt

Question 28

Case studies

Answer 28

• Causes/ effects and management of volcanoes (Monsterrat)
• Why do people live near volcanoes? (Monsterrat)
• Causes/effects and management of an earthquake (Haiti)
• Why do people live in earthquake zones? (California)

Question 29

Case study: Why do people live in Earthquake zones?

Answer 29

California

• benefits outweigh costs
• Job opportunities
• tourism
• popular city
• good education and health care
• very famous landmarks
• celebrities and films are there
• it’s a fun place to be
• nice landscape