Topic 1: Tectonic activity

GCSE geography edexcel B

Tectonic Hazards

Events occuring due to movement or deformation of the earth's crust with the potential to cause damage to property and loss of life. Examples include earthquakes, volcanic eruptions and tsunamis.

Order of Earth's layers

crust, lithosphere, asthenosphere, mantle, outer core, inner core

Crust:

Where?

Types?

Physical State?

Thickness?

Upper layer of earth

Oceanic and continental

Solid

Less than 100km

Mantle:

Where?

Includes?

Thickness?

Underneath the earth's crust

Lower part of the lithosphere, the asthenosphere, lower mantle

2800km

The core:

Where?

Includes?

Thickness?

Centre of the earth

Outer and inner core

3478km

Lithosphere:

Where?

Includes?

Physical state?

Temperature?

Density?

Very top of mantle

Crust and top layer of mantle

Made of peridotite, cool and brittle solid

0 to 900 degrees Celsius

Low - 2.7 to 3.3g/cm^3

Asthenosphere:

Where?

Physical state?

Temperature?

Density?

In the mantle

Semi-molten

900-1600 degrees Celsius

Low-Medium - 3.3 to 4.4 g/cm^3

Lower mantle:

Physical state?

Temperature?

Density?

Solid

1600-4000 degrees Celsius

Medium - 4.4-5.6 g/cm^3

The outer core:

Physical state?

Temperature?

Density?

Liquid

4000 to 5000 degrees Celsius

High - 9.9 to 12.2 g/cm^3

Inner core:

Physical state?

Solid

Continental crust

where?

thickness?

made of?

density?

permanent or created and destroyed?

under the land

30-40km, can reach 70km

granitic rock, igneous granite

2.7g/cm^3 (less dense than oceanic)

permanent

Oceanic crust

where?

thickness?

made of?

density?

permanent or created and destroyed?

under the sea

5-8km

basaltic rock, igneous basalt

denser than continental, almost 3.0g/cm^3

created and destroyed

Geoshpere definition

The rocks that make up the solid mass of the Earth, from the crust to the core

Mantle definition

The layer beneath the crust, containing liquid magma/ molten

Oceanic crust definition

Found under the ocean (the sea bed), mainly basalt, denser than continental

Continental crust definition

Forms the land and is mainly granite, less dense than oceanic

Tectonic plate definition

A large section of the Earth's crust

Plate boundary definition

The edge of a plate where two plates meet

Lithosphere definition

The uppermost part of the earth including the crust and the top part of the mantle

Inner core definition

The inner most part of the Earth. It is solid and extremely hot

Convection currents definition

When heat rises from the core through the mantle, moving the tectonic plates above

Tectonic plates (9)

Pacific, North American, South American, Nazca, African, Eurasian, Indian, Antarctic, Australian

California plate boundary?

Conservative boundary

West coast South America plate boundary?

Destructive (convergent) plate boundary

Iceland plate boundary?

Constructive (divergent) plate boundary

Himalayas Plate Boundary?

Convergent (collision) plate boundary

Geothermal heat definition

The heat from inside the Earth which is produced by the radioactive decay in elements such as uranium and thorium in the core and the mantle

Radioactive decay definition

When atoms of naturally unstable and radioactive elements release particles from their nuclei and give off heat

Why do tectonic plates move?

Radioactive decay of elements such as uranium and thorium in the core and mantle creates geothermal heat which raises the core's temperature to over 5000°C. This means that the inner core in very hot. As a result, this causes the mantle to be heated, creating 'plumes' areas where magma rises upwards towards the crust. This movement initiated convection currents in the mantle. The 'sideways' movement of magma within the upper mantle drags the plates with it, causing them to move

When describing the global distribution of earthquakes and volcanoes?

- place names

- compass directions

- overall plate boundaries

- patterns (for eg linear, patterns of belts/bands)

- concentrated/limited

Divergent/constructive plate boundary

1) 2 oceanic plates move apart

2) As the 2 plates move apart, magma rises to fill the gap

3) This causes volcanoes but because the magma can escape easily, the eruptions tend to be less violent

4) Earthquakes are also formed as the 2 plates jolt apart

Convergent/destructive (subduction)

1) An oceanic plate pushes against a continental plate

2) The oceanic plate is subducted below the continental plate as it is denser

3) the oceanic plate melts as it descends into the mantle

4) Friction between the plates can result in slippage which creates large earthquakes

5) The newly created magma forces its way through the continental plate under huge pressure causing violent eruptions

Conservative plate boundary

1) 2 plates slide sideways relative to each other, either in opposite directions or the same direction but 1 faster than the other

2) this movement causes friction and pressure builds until the plates slip and large earthquakes are caused

3) No volcanic eruptions can occur

convergent/ destructive (collision) plate boundary

1) 2 continental plates move together

2) as the plates collide, the material between them buckles

3) the plates colliding cause large earthquakes

4) Volcanic eruption do not occur

How are volcanoes formed?

When molten rock from a magma chamber inside the Earth erupts onto the surface through a vent in the lithosphere

Volcanic Explosivity Index (VEI)?

A relative scale based on the volume of erupted tephra (rock fragments and particles ejected by a volcanic eruption) that enables explosive explosive eruptions to be compared with one another

Shield volcanoes:

Appearance and material?

Boundary type?

Magma type?

Explositivity?

Examples?

Wider but shorter, layer of just lava

Divergent or hotspot

Basaltic, extremely fluid (low viscosity)

Little explosive activity but frequent eruptions (VEI 0-4)

Eg Mauna Loa, Hawaii, USA,

Eg Eyafialiajokuil, Iceland

Composite volcanoes:

Appearance and material?

Boundary type?

Magma type?

Explositivity?

Examples?

Narrower but taller, made if layers of ash and lava

Convergent

Andesitic - less fluid (high viscosity)

Explosive eruptions (VEI 4+)

Eg Mt Pinatubo, Phillippines

Eg Mt st Helen's, USA

Composite and shield volcanoes differences

Shield:

Made of basaltic lava which has a lower silica content meaning that the lava is less viscous (gloopy)

Gases can escape easily in basaltic magma so they are less violent

Lava flows long distances before cooling

Composite:

Made if Andesitic lava which has a higher silica content meaning that the lava is more viscous (less fluid)

Gases cannot escape easily resulting in more violent eruptions

Lava does not flow freely

Earthquake definition

Intense vibrations within the Earth's crust that make the ground shake. They are caused at plate boundaries, by sudden plate movements

Focus definition?

The point of rupture - where the earthquake actually happens underground

What do shock waves do?

Shock waves/ seismic waves radiate out from the focus

Epicentre definition?

The point on the ground surface directly above the focus, where the greatest force of the earthquake is felt

Magnitude definition?

A measure of the amount of energy released in an earthquake

Instrument used to measure earthquake magnitude?

Seismometer

Scale used to quantify the energy released?

The Richter Scale

Secondary hazards - tsunami causes?

1) oceanic plate is subducted underneath continental plate. Friction stresses and bends the continental plate downwards as the oceanic plate moves underneath it

2) When the pressure gets too great, plates slip and the continental plate rebounds upwards.

3) The rebound of the continental plate (mega-thrust) causes displacement of water above.

4) Displaced water is pulled back down by gravity and causes waves to move away from the point of displacement

5) Waves remain small out in the deep ocean

6) But when waves move into shallow water, wave shoaling occurs and their height (amplitude) is increased dramatically

Causes of why some earthquakes have worse impacts that others

- Earthquake magnitude

- Proximity to cities

- Focus depth

- Accessibility (Eg Emergency services)

- wealth/ Economic development (e.g prediction, planning, preparation)

- Population density (E.g more people, more buildings that fall)

- Time of day/ week/ year (Eg holidays- more people away)

- Relief (e.g low lying areas suffer more)

Primary impacts of earthquakes

- Loss of life and injury

- destruction of buildings

- destruction of transport networks

- loss of jobs and businesses

- power supplies damaged

- damage to the environment

Secondary impacts of earthquakes

- decrease in population

- homelessness increases, may be expensive for people to repair homes

- speed of aid and emergency vehicles is slowed

- impact on economy, slows economic growth

- food shortages, famine

- means of communications removed

- loss of vegetation and habitats

Nepal Earthquake:

Date?

Time of day?

Epicentre location?

Magnitude?

Depth of focus?

GDP per capita?

Population density?

Death toll?

Homes destroyed?

Economic costs?

Aftershock details?

Date: April 25th 2015

Time of day: 11:56 am

Epicentre location: Gorkha District

Magnitude: M 7.8

Depth of focus: 8.2km

GDP per capita: $850

Population density:Mostly rural except Kathmandu

Death toll: 9000

Homes destroyed: 160,000

Economic costs: $10 billion

Aftershocks: Close to Tibet boarder, numerous

Primary impacts (Nepal)

- power, water and communications severely affected

- many historical sites and landmarks damaged e.g Durbur square in Kathmandu

Secondary impacts: landslides and avalanches (Nepal)

- landslides and avalanches triggered by ground shaking, causing widespread damage to infrastructure, blocking roads and trapping people under snow and rubble.

- avalanches on Mount Everest killed 19 people

- landslides blocked rivers e.g Kali Gandalf river, people had to be evacuated in case of flooding

Primary impacts definition

Those caused by the earthquake itself

Secondary impacts definition

Those caused by other hazards created by the earthquake

Short term relief in Nepal

- for the first 24 hours after incident, there was no aid sent to the affected area. The isolated location and poor transport links made it difficult for aid organisations to reach the area quickly.

- within a few days, international aid arrived from the UK, India and china. They brought search and rescue teams, medical support and essential supplies. Over US$1 billion in international aid from India and China

- half a million tents were provided after the earthquake, providing shelter for the homeless

Planning, preparation, prediction in Nepal

- in 2015 there was very little earthquake response planning despite it being one of the most disaster prone countries in the world

- Nepal centre of disaster management was established in 2002 to help mitigate impact of any disasters

- emergency supplies were stockpiled but not in sufficient amounts

- not possible to predict earthquakes but there are seismometers in place around Nepal to monitor the strength of earthquake waves

Long term responses (Nepal)

- rebuilding is taking place, making buildings more resistant to earthquakes whilst also preserving the unique heritage of the area.

- many buildings are being rebuilt as one storey homes to make them earthquake proof, however this is not ideal for larger families.

- after 4 years there are still 230,000 in temporary accommodation

Japan Earthquake:

Date?

Time of day?

Epicentre location?

Magnitude?

Depth of focus?

GDP per capita?

Death toll?

Buildings collapsed?

Economic costs?

Aftershock details?

Date: March 11th 2011

Time of day: 2:46 pm

Epicentre location: 72km east of Tonoku, in the Pacific Ocean

Magnitude: M 9.0

Depth of focus: 24km

GDP per capita: $38,900

Deaths: 18,500

Buildings damaged: 123,000

Economic costs: $300 billion

Aftershocks: Hundreds, including 5 that were M7.0 or higher within 3 months

Primary impacts: earthquake damage (Japan)

- Less than 5% of deaths (approx 700)

- In Tokyo, railway services suspended, 20,000 stranded at stations

Secondary impacts: tsunami damage (Japan)

First tsunami wave hit less that an hour after the quake, heights up to 39 metres, distances in land up to 10km, 561 square km flooded

- Over 90% of total death toll was from drowning

- Most of building collapse and damage due to tsunami

- 340,000 people were displaced in the Tohoku region

- Sendai airport flooded , damaged major ports

- Over 25 million tonnes of debris

Secondary impacts: radiation threat (Japan)

- Cooling system failure of Fukushima Nuclear Power plant, which resulted in a level 7 nuclear meltdown

- release of radioactive materials

- In 2013, 300 tons of radioactive water was still leaking into the Pacific Ocean each day

- Some radioactive chemicals detected off North American Coast

Short term relief in Japan

- Japanese government mobilised the self-defence forces to assist in search, rescue and recovery

- Japan received help from the Us military and international teams were sent from many countries incl China and India

- hundreds of thousands of people who had lost their home or were evacuated used temporary shelters set up in schools and other public buildings.

Japan earthquake planning, preparation and prediction

- Residents of Tokyo received a minute of warning before the strong shaking hit

- Country's stringent seismic building codes and early warning system prevented many deaths

- People also received texted alerts of the earthquake and tsunami warnings

Japan earthquake longer term response and recovery

- Upgraded tsunami warning system

- Earthquake drills every year in schools and in workplaces

- Earthquake engineers examined the damage, looking for ways to build buildings more resistant to quakes and tsunamis

Hotspots definition?

Volcanoes that are formed away from plate boundaries

Hotspot formation?

Formed by a plume of superheated rock rising very slowly through the mantle. Once it reaches the upper mantle, it causes the asthenosphere and the lithosphere to melt. The magma produced then rises through the weaknesses in the crust and erupts at the Earth's surface