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Theme D: The Restless Earth Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Plate Tectonics (Theory)

The core of the earth is made up of dense materials (iron) & nickel, with a liquid outer core and solid inner core.
The mantle of the earth is the thickest layer of the earth, made up of silicate rocks which due to high temper­atures (3500 degrees) remain molten and float about.
The crust is the thin layer. Broken into several pieces known as plates which move due to convection currents within the mantle.
Theory of Plate Tectonics
The surface of the earth is moving - less than 1cm a year, but over many years these small movements have a big impact. Hard crystal rock sits on a layer of molten mantle rock - these sections of crystal rock are called plates and they are moved by pressure and heat from inside the earth.
The theory of plate tectonics is credited to Alfred Wegener.

Diagram of Earth

Convection Currents

Convection currents are within the mantle and are heated by magma in the outer core. Due to heat it is less dense and the magma rises. After hitting the crust, the magma is forced to spread out. After heat spreads out it cools and sinks back down, this is continuous and causes movement in crust. While currents descend they drag crust into mantle (destr­uctive margin)

Convection Currents

Plate Types

Contin­ental Plates
Oceanic Plates
35-100km - THICK
6-10km - THIN
Old rocks
Young rocks
'Light' rocks which are less dense
'Heavy' rocks which are more dense
Hard to destroy
Easier to destroy
Does not easily sink into mantle
Can sink into mantle

Plate Margins

Constr­uctive Plate Margins - Mid Ocean Ridges
One constr­uctive margin is found in the middle of the Atlantic ocean. Here the Eurasian and North American plates are being pulled apart, moving away from one another. This means the Atlantic ocean is getting wider apart by approx. 3cm per year. The movement causes regular but weak earthquake activity. Magma wells up from mantle to plug the gap so there is often frequent gentle volcanic activity. This rising of material pushes up crust at either side slightly, thus creating a mid-oc­eanic ridge.
Destru­ctive Plate Margins - Oceani­c-C­ont­inental Crust
An example would be found in South America. Here the Nazca plate, made of Oceanic crust, is disapp­earing below the American plate. At plate margin, dense oceanic crust is pushed downwards. As it is dense it falls below its normal level, creating a deep ocean trench (Peru-­Chile). Movement is not smooth due to rough surface friction. Plates may become stuck for years until pressure is greater than friction. Will cause plates to jolt and move suddenly. Felt on Earth's surface as an earthq­uake.
Destru­ctive Plate Margins - Oceani­c-O­ceanic Crust
Violent activity. An oceanic crust margin where oceanic crust and oceanic crust meet. Has many similar features to first type of destru­ctive margin. As the oceanic sinks into mantle, it melts and creates a less dense material than surrou­nding rock. Deep ocean trench forms where dense material pushed down into mantle. Can be very deep. Magma then rises upward and may erupt through crust to create volcanic island.
Collision - Contin­ent­al-­Con­tin­ental Crust
Where two contin­ental plates meet is a collision zone. Crusts of both plates buckle and fold upwards. Two sets of fold mountains overthrust one another, creating large range of fold mountains. Little material melting and that which does not melt cannot make it through high mountains to make volcano. Instead, magma forms large intrusions into mountain range. Magma cools slowly to form granite cores to mountains.
Conser­vative Plate Margins - Fault Lines
Violent activity. At conser­vative margins, such as San Andreas fault line (Calif­ornia) two plates try to slide past one another. Friction causes plates to stick, pressure is built up and is eventually released as an earthquake when plates jolt suddenly. Crust is neither created or destroyed so therefore no volcanic eruptions.

Constr­uctive Plate Margin

Destru­ctive Plate Margin

Collision Zones

Conser­vative Plate Margin


Basic Rocks

Very hard, dark grey rock. Feels rough and heavy. Small glittery specks.
Rough texture and speckled colour. Often pink or grey.
Worktops, graves­tones, constr­uction, decoration
Formed from grains of sand. No crystals. Feels rough and hard.
Statues, constr­uction
Grey, white or yellow. May be hard and contain fossils and layers. Porous.
Neutra­lises acidic soil, glass, some buildings, cement
Dark grey rock with easily split layers. Smooth, flat surface. Imperm­eable.
May be pure white or have swirls or bands of colour. Rough and grainy when unpoli­shed.

Basic Rock Types

Igneous Rocks
These include basalt and granite and they have been formed by cooling and solidi­fying of molten rock (magma) from underneath the earth's crust. This molten rock is called lava on the surface of the earth. Crystals are usually evident in the rock. However, if the rock cools quickly as the lava hardens on the surface, there will be little evidence of the crystals (basalt). If the magma is cooled slowly underg­round, then a cystalline structure will be more evident (granite).
Sedime­ntary Rocks
Limestone and sandstone are formed by sediments being built up in layers, usually under water over a long period of time. As more and more eroded material is added, pressure pushes air and water out and the sediment gets cemented into rock.
Metamo­rphic Rocks
Slate and marble have been changed through the addition of pressure or heat. The rocks would originally have been igneous or sedime­ntary - marble once was limestone. Metamo­rphic rocks are hard and resistant to erosion.

Managing Earthq­uakes


Case Study - Indian Ocean Earthquake 2004

Spatial Context
26th December 2004. Sumatra, Indonesia (West Coast). Magnitude of 9.2, duration of 10 minutes. Australian and Sunda plates respon­sible.
- Major fault line where Australian plate meets Sunda plate. Part of a subduction zone, 15m slippage along fault line in two stages causing prolonged earthq­uake.
- Ocean floor rose by several metres, causing a large tsunami.
Short Term Impacts - People
- 66% of Sri Lanka fishing fleet destroyed which had economic implic­ations due to fishing being direct employment for a quarter of a million.
- 125,000+ injured
- 1.1mil tempor­arily displaced due to coastal devast­ation
Long Term Impacts - People
- Death toll just under 187,000 - a third of which being children
- In Maldives, 17 coral attol islands had freshwater supply contam­inated. Inhabi­table for decades.
- Widespread mental trauma due to being unable to uphold Islamic belief of having to bury deceased.
- Rebel group ceased fire against govern­ment.
Short Term Impacts - Enviro­nment
- 30m high tsunami; countries affected on all sides of Indian ocean
- Whole earth vibrated by 1cm due to energy released, 1502 times that of atomic bomb on Hiroshima.
- Afters­hocks continued for 3 to 4 months afterwards
Long Term Impacts - Enviro­nment
- Raising of seabed reduced Indian ocean capacity and raised global sea level by 0.1mm
- Coastal ecosystems of affected areas severely damaged; mangroves and coral reefs destroyed.
- Massive release of energy expected to shorten length of day by 2.68 micro seconds; change to earth's shape.
Management Response
- Area affected used to minor quakes and volcanic eruptions but made up of poor LEDCs and lack resources to have scale and quality of response that MEDCs have.
Before the Earthq­uake; Prediction and Precaution
- No early warning system to record underg­round quakes. Simeulue island evacuated coastal areas as tremors were felt; fled to inland hills.
- Tilly Smith Phucket recognised warning signs and helped evacuate beach.
Immediate and Longterm Action After Earthquake
- World pulled together to provide aid. Over £7 billion donated from national government and non-go­ver­nment operat­ions.
- Sri Lanka, Indonesia and Maldives declared state of emergency. Strict laws implem­ented to keep order.
- Review of poor earthquake and tsunami warning system around Indian ocean took place and in June 2006, 25 new seismo­graph stations relaying inform­ation to national tsunami centres became operat­ional.
How prepared is Indonesia for a similar earthquake today?
- City of Banda Aceh rebuilt by 2014.
- Park and memorial site built around 2,600 ton ship that washed up on shore.
- Population back to 250,000 (almost the same as 2004).
- New highways and vibrant night life.
- Banda Aceh has 3/4 evacuation centres with open ground floors to allow tsunami waters to pass through.
- Country's location on border of a number of dangerous fault lines between tectonic plates means another large earthquake is inevit­able. One of the most notable is Sunda, megathrust fault line, parallel to Sumarta and Java Islands. Even an instan­taneous alert would not give residents enough time to reach high ground (30 minutes)

The Global Distri­bution of Earthq­uakes

An earthquake is described as a "­fault rapture that generates seismic waves".
This occurs when rocks on either side of a weakness in the earth's crust (fault) causes the ground to vibrate and shake.
When a movement takes place deep within the earth, the vibrations (seismic waves) travel from the focus (where the earthquake originally occurs) and from here to the surface. Epicentre is the place on the earth's surface which is above the focus - this is where the intensity or the magnitude of energy released is felt the most.
Seismic waves are recorded by a seismo­graph. During an earthquake the base of the seismo­meter will move horizo­ntally and the motion is converted into electrical voltage and recorded on paper.
The strength of an earthquake is referred to as its magnitude and in 1935 Charles Richter developed his logari­thmic scale - an earthquake of 6 will be ten times greater than a strength 5.

After Effects of Earthq­uakes

Liquef­action occurs when an earthquake hits an area and shakes the wet soil. The shaking causes the water within the soil to start and rise up to the surface, and this process turns solid soil and rock into a liquid mud. Buildings will start to sink and tip over as the support for the founda­tions is waterl­ogged and cannot maintain the weight of the buildings.
A tsunami is a large wave which is created when an underwater earthquake sends shockwaves through the water, causing a surge of water to move towards the coastline. The energy can travel for thousands of miles across the ocean.

Volcanoes: Charac­ter­istics & Conseq­uences

A volcano is a cone shaped mountain built up from hardened ash and lava from molten materials which can erupt onto the earth's surface.
During an eruption a volcano may eject ash, hard bits of rock (volcanic bombs), lava or gasses.
Composite Volcanoes
(Forma­tion) Found at destru­ctive plate margins.
Composite volcanoes have very steep sides and a narrow base.
Lava builds up in a magma chamber underneath the volcano. This can be added to as more oceanic crust melts at the plate margin.
The lava is very thick (acid) and so clogs up the main vent of the volcano, causing a "plug effect­".
The pressure build-up causes an explosion which blows out ash, gas and lava.
The neck of the volcano is then cleared which allows the lava to flow out of the crater.
The layers of lava become the sides.
Alternate layers of ash and lava (ash is 1st in on eruption)
Very violent eruptions (volcanic bombs)
Slow, thick lava.
Narrow base due to slow moving lava.
Shield Volcanoes
These are found on constr­uctive plate margins.
They also occur at hot spots under the earth's surface (not on plate bounda­ries, but forming a chain of volcanic islands eg. Mauna Loa, Hawaii, Usa.)
Shield volcanoes have gently sloping sides and are much wider than composite volcanoes.
They erupt freque­ntly; gentle eruptions.
The lava is very fast and runny - basic lava (basalt), with little ash. This spreads easily and cools to form the gentle sides.
They usually occur on constr­uctive margins where the sea floor is spreading at a mid-ocean trench.
Classified as at least 1000km cubed of material erupted during explosion. Create wild depres­sions - Calderas with high ridge of land. Caldera forms when a volcano erupts so violently it collapses in on itself. Magma and pressure build up overtime, ending in a violent disruption which can disrupt the world.

Composite Diagram

Shield Diagram

Super Volcano Diagram

Case Study - Yellow­stone National Park, USA

Located in Wyoming, North West of USA.
Background Inform­ation
A superv­olcano is classified when at least 1,000km cubed of material is erupted during the explosion. The world's first national park, Yellow­stone National Park, has over 4 million visitors a year and sits on top of a superv­olcano with a chamber 80km long and 20km wide.
Potential Impacts - People
- Greatest impact in USA, almost everyone killed within 1000km blast.
- 90,000 may die from inhaling ash (cement like in human lungs). Even east coast immobi­lised by just 1cm ash.
- Many buildings destroyed as only takes 30cm dry ash to cause roof to collapse.
- Water supplies undrin­kable.
- Transport in USA severely disrupted
- Air travel disrup­tions. Badly affected causing major disruption in other countries and to business.
Potential Impacts - Enviro­nment
- Could inject 2000mil tonnes of sulphur into earth's atmosp­here. Would cloak globe in 2-3 weeks. Aerosols reflect sunlight, reducing amount of energy reaching lower atmosphere and earth's surface, cooling them.
- Global annual temper­ature would drop by up to 10 degrees. Could last from 6 to 10 years.
- Crop failures and 'little' ice age.
- 67 species of mammals would die causing a disrupted ecosystem for decades.
- It would take 10 years before any vegetation becomes re-est­abl­ished.
- Acid/p­olluted rain infilt­rating water systems killing fish.