Restless Earth


Restless Earth


Why is the earth’s crust unstable?

The structure of the earth

Inside the earth it's hot - really hot. We know that because of the molten lava that spews from volcanoes. Also, in some places, you get hot springs and geysers. The earth isn't a solid bal of rock. It's made up of different layers like an apple. The skin/peel is the crust, the white fleshy part the mantle and where the seeds are the core. The earth's crust is divided into large pieces, called plates. It's unstable because these plates move very slowly. The different plates meets at plate margins, or boundaries. There are four main types of plate margins:     Constructive - where the plates are moving apart Conservative - where the plates slide past each other Collision - where the plates push against each other often forming mountains - Himalayas Destructive - where the plates collide Excellent Animations - mentalSciences/Educational%20Materials/Documents/elearning/module06swf.swf


Structure of the earth


Why do the plates move?

Types of crust

The Earth's crust is made up of:   Oceanic crust - is found under the ocean Continental crust - is found underneath the continents or land masses

Oceanic Crust

5-10km thick Dense Sinks into the mantle when oceanic and continental crust meet

Continental Crust

25-100kn thick Less dense Doesn't sink The oldest is only 180 million years old Very old - 3-4 billion years old Forms constantly at constructive plate margins New crust isn't formed Destroyed at destructive plate margins Cannot be destroyed 4


Plate margins

You need to be able to draw simple diagrams to show how each of the plate margins work. You need to make sure you can add three labels and write a description. Video links Plate tectonics - tectonics/5724.html

Excellent video - theory/3059.html

The link here shows some animations of how plate margins move -

Excellent animations - mentalSciences/Educational%20Materials/Documents/elearning/module06swf.swf




Distribution of hazards

For each tectonic landform or hazard you need to be able to describe where they are found. You should state each of the following:     They are found on or near plate boundaries Say where you find most of them - continents/oceans Say where you find very few of them - continents/oceans Try to name examples - e.g. Pinatubo, Volcano; Kobe, Japan and The Andes, Young Fold Mountains

Where are fold mountains found and ocean trenches found?

Mountain ranges, like the Himalayas and the Andes were formed quite recently in Geological time. That means tens of millions of years ago, rather than hundreds of millions! The map below shows the distribution of the hazards. 9

Where are volcanoes found?

You tend to find volcanoes in long belts, as the map below shows. The biggest belt wraps around the Pacific Ocean. It's called 'The Pacific Ring of Fire'. There's another one running down at the middle of the Atlantic - Mid-Atlantic Ridge.

Where are earthquakes found?

The world map below shows the global pattern of earthquake activity. Earthquakes tend to occur in long belts. The biggest one goes round the whole Pacific Ocean, and another big one runs down the middle of the Atlantic Ocean. These earthquake belts follow the plate margins. 10

Fold Mountains The Formation of Fold Mountains

In large Geosynclines (depressions in the sea) material and sediment is deposited into it.

Over time the Geosyncline becomes completely full. Later the two plates start to move towards each other. This leads to the sediments becoming compressed and turning into rock.

Later as the plates compress the rock more they start to fold and turn into fold mountains. (See diagrams below).

When fold mountains are formed various the rock get folded in a variety of ways. These have specific 11

names which you have to learn for the exam.    

Geosyncline - a large depression in which sediment has been deposited into it Anticline - the upfolds of folded rock Syncline - the downfolds of folded rock Nappes - when the rock has been severely folded and faulted it forms these


Fold mountain case study: The Andes

The Andes and its people The Andes is a range of young fold mountains formed some 65 million years ago. It is the longest range of Fold Mountains in the world at 7,000km and extends the length of South America. The Andes are about 300km in width and have an average height of 4,000m


      Subsistence farmers grow a variety of crops on the steep slopes including potatoes The use of terraces creates areas of flatland on the slopes ± the flat areas retain water and limit the movement of soil downslope Most crops are grown in the lower valleys Cash crops such as soybeans, rice and cotton are grown Llamas are used for carrying irrigation materials and buildings to inhospitable areas. Llamas are also used for meat and milk, and their wool is used in clothes as well as rugs


 The Andes has a range of important minerals such as tin, silver, nickel and gold  The Yanacocha gold mine is the largest in the world and a joint venture between a Peruvian mining company and a US-based one  Local water supplies can be contaminated by the treatment process  The local town of Cajamarca has grown from 30,000 (when the mine was built)inhabitants to 240,000 in 2005 and brought a lot of jobs  However, this growth also brings many problems, including a lack of services and an increased crime rate

Hydroelectric Power (HEP)

 The steep slopes and narrow valleys that limit farming are an advantage for  HEP   They can be dammed easily The steep slopes allow for a rapid flow of water into rivers from rainfall and snow melt also increases water flow  The Yuncan project dams the Paucartambo and Huachan rivers in north-east Peru


 There are many attractions such as Machu Picchu home of the lost Inca tribe as well as the indigenous wildlife.  However, tourism can bring problems such as litter, pollution and soil erosion on footpaths 13

Types of volcanoes and formation


Volcano case studies

You should make sure you are familiar with the following three case studies:   Nyiragongo, Democratic Republic of Congo - Poor Country Mount St. Helens, USA - Rich Country

Key terms:

Primary effects: the immediate effects of the eruption, caused directly by it Secondary effects: the after-effects that occur as an indirect effect of the eruption on a longer timescale Immediate responses: how people react as the disaster happens and in the immediate aftermath Long-term responses: later reactions that occur in the weeks, months and years after the event


The video below contains more information on the primary and secondary effects of a volcano On 17th January 2002 Nyiragongo volcano in the Democratic Republic of Congo (DRC) was disturbed by the movement of plates along the East African Rift Valley. This led to lava spilling southwards in three streams.

The primary effects

45 people - The speed of the lava reached 60kph which is especially fast. The lava flowed across the runway at Goma airport and through the town splitting it in half. The lava destroyed many homes as well as roads and water pipes, set off explosions in fuel stores and powerplants and killed

The secondary effects

- Half a million people fled from Goma into neighbouring Rwanda to escape the lava. They spent the nights sleeping on the streets of Gisenyi. Here, there was no shelter, electricity or clean water as the area could not cope with the influx. Diseases such as cholera were a real risk. People were frightened of going back. However, looting was a problem in Goma and many residents returned within a week in hope of receiving aid.


- In the aftermath of the eruption, water had to be supplied in tankers. Aid agencies, including Christian Aid and Oxfam, were involved in the distribution of food, medicine and blankets.

Mount St. Helens

Mount St. Helens is one of five volcanoes in the Cascade Range in Washington State, USA. The volcano erupted at 8:32am on 18th May 1980.


- An earthquake caused the biggest landslide ever recorded and the sideways blast of pulverised rock, glacier ice and ash wiped out all living things up to 27km north of the volcano. Trees were uprooted and 57 people died.

Immediate responses

- helicopters were mobilised to search and rescue those in the vicinity of the catastrophic blast. Rescuing survivors was a priority, followed by emergency treatment in nearby towns. Air conditioning systems were cleaned after by clogged with ash and blocked roads were cleared. Two million masks were ordered to protect peoples lungs.

Long-term responses

- Buildings and bridges were rebuilt. Drains had to be cleared to prevent flooding. The forest which was damaged had to be replanted by the forest service. Roads were rebuilt to allow tourists to visit. Mount St. Helens is now a major tourist attraction with many visitor centres. 15

Monitoring Volcanoes

The eruption of Mount St. Helens was expected and prepared for, but in spite of the monitoring that had taken place, the exact date and time of the eruption took people by surprise. There are some signs to look out for:          Earthquakes are a frequent sign of an impending eruption and their frequency and strength can be recorded Bulging on one side of the volcano - the swelling is obvious and a clear sign of magma moving Tiltmeters can identify small, subtle changes in the landscape Global Positioning Systems (GPS) use satellites to detect movement of as little as 1mm Satellites can detect changes in surface temperature Digital cameras can be used to check for changes in volcanic activity Gases being emitted from the vent change before an eruption Robots called 'spiders' are often deployed to look inside the rim of the volcano The past frequency of eruption is often investigated: the gap between eruptions and the pattern of lava flows, ash movement and lahars can tell people about how the volcano is likely to behave This technology allows people to prepare for an eruption by organising the evacuation of people and arranging supplies 16



Causes of earthquakes

What causes earthquakes? Earthquakes occur at plate margins because of friction - the plates try to move and get stuck. Pressure builds up as the plates keep trying to move. If the pressure is released slowly, we hardly notice the movement. But if the pressure is released suddenly, it can send out huge pulses of energy - causing the Earth's surface to move violently. Earthquakes occur at all four plate margins:     destructive margins - when one plate tries to sink below the other. The pressure resulting from the sinking of the subducting plate and its subsequent melting can trigger strong earthquakes as this pressure is periodically released. collision zones - where the plates are pushing together. Strong earthquakes constructive margins - when both plates try to move/slide past each other. These earthquakes tend to be less severe than those at destructive plate margins. The friction and pressure caused by the plates moving apart is less intense than at destructive plate margins. conservative margins - when plates moving alongside each other get stuck. These are very strong earthquakes. Here, where the plates slide past each other, the plates tend to stick for periods of time. This causes stresses and pressure to build. The release of the pressure occurs in a sudden, quick release of the plates and the result is an earthquake. 18

Measuring the strength of earthquakes There are two main methods as detailed below: 19

Earthquake case studies: Kobe, Japan; Sichuan, China

The Sichuan earthquake, China - Poor country

On 12th May at 14:28pm, the pressure resulting from the Indian Plate colliding with the Eurasian Plate was released along the Longmenshan fault line that runs beneath. This led to an earthquake measuring 7.9 on the Richter scale with tremors lasting 120 seconds.

Primary effects

 69,000 people were killed  18,000 missing  374,000 were injured  between 5 -11 million people were missing  80% of buildings collapsed in rural areas such as Beichuan county due to poorer building standards  5 million buildings collapsed

Secondary effects

 Communication were brought to a halt – neither land nor mobile phones worked in Wenchuan 20

 Roads were blocked and damaged and some landslides blocked rivers which led to flooding  Fires were caused as gas pipes burst  Freshwater supplies were contaminated by dead bodies

Immediate responses

 20 helicopters were assigned to rescue and relief effects immediately after the disaster  Troops parachuted in or hiked to reach survivors  Rescuing survivors trapped in collapsed buildings was a priority  Survivors needed food, water and tents to shelter people from the spring rains. 3.3 million new tents were ordered.

Long-term responses

 Aid donations specifically money – over £100 million were raised by the Red Cross  One million temporary small were built to house the homeless  The Chinese government pledged a $10 million rebuilding funds and banks wrote off debts by survivors who did not have insurance

Kobe, Japan


The three P’s

The three Ps provide the key to trying to reduce the impact of earthquakes.   


involves trying to forecast when an earthquake will happen. Japan tries to monitor earth tremors with a belief that warning can be given, but this did not happen at Kobe. Foreshocks do occur, but on a timescale useful to evacuation. Experts know where earthquakes are likely to happen, but struggle to establish when. Even looking at the time between earthquakes in a particular area does not seem to work. Similarly, experts struggle to pinpoint exactly where along a plate margin they will occur. Animal behaviour has been used in the past


involves building to an appropriate standard and using designs to withstand movement.


involves hospitals, emergency services and inhabitants practising for major disasters, including having drills in public buildings and a code of practice so that people know what to do to reduce the impact and increase their chance of survival. Video showing how to prepare for an earthquake - for-earthquakes/5723.html


The diagram below shows how a building may be earthquake-proofed: 23


How tsunamis form

Tsunamis are usually triggered by earthquakes. The crust shifting is the primary effect; a knock-on (secondary) effect of this is the displacement of water above the moving crust. This is the start of a tsunami. A normal, wind-driven wave may have the length of a 100m from crest to crest, but a tsunami may be 200km in length. The heights also greatly differ: 2m for a normal wave versus 1m for a tsunami out at sea. Tsunamis move at speeds of around 800kph, rapidly approaching the coast almost unnoticed. As they near the land they slow, reduce in length and gain in height. A collection of excellent BBC videos: The Asian Tsunami: Causes and effects - causes-and-effects/3195.html

The Asian Tsunami: Damage to coral reefs - tsunami-damage-to-coral-reefs/3200.html

The Asian Tsunami: Disease - disease/3197.html

The Asian Tsunami: Effects on tourism - effects-on-tourism/3201.html

The Asian Tsunami: Eyewitness accounts in Sri Lanka - asian-tsunami-eyewitness-accounts-in-sri-lanka/3198.html

The Asian Tsunami: Predicting a future event - tsunami-predicting-a-future-event/3203.html

The Asian Tsunami: Variable impacts - variable-impacts/3202.html

Awesome series of animations -

The effects of the Boxing Day tsunami 2004

The earthquake that caused the Boxing Day tsunami was estimated to be between 9.0 and 9.3 on the Richter scale - one of the largest earthquakes ever recorded. The tsunami then moved as a series of ripples' across the Indian Ocean which built up as massive waves when they approached the land. It was one of the worst natural disasters in history - nearly 300,000 people killed or disappeared completely. Loss of tourist income as tourists stayed away from the affected areas. 24

Responses to the tsunami Immediate responses Long-term responses

    clean water, food, tents and plastic sheeting arrived as aid $7 billion was donated worldwide for the affected countries people in the UK donated £300 million (more than the government) The UN's World Food Programme provided food and for more than 1.3 million people   tsunami warning system - the disastrous effects of the Boxing Day tsunami led to the setting up of a tsunami early warning system in the Indian Ocean. Formal warnings are now sent to countries throughout the region if there's a tsunami threat. These warnings are then passed on to individuals via radio, television and e-mail or by bells, megaphones and loudspeakers attached to mosques restoring mangrove swamps - the tourist industry in Thailand and Sri Lanka had grown rapidly before the tsunami. Many coastal areas had been cleared of mangrove swamps to make way for hotels. but mangroves act as a natural barrier - absorbing wave power and helping to protect coastlines and inland areas from tsunamis. After 2004, some projects to restore mangroves were started e.g. the Green Coast Project in Aceh, Indonesia. The new mangroves will help to increase the protection for future tsunami, and also help to provide a livelihood for people affected by the 2004 tsunami, because mangroves are good breeding ground for fish. 25


Crust: the outer layer of the earth Plate: a section of the earth's crust Plate margin: the boundary where two plates meet Mantle: the dense mostly solid layer between the outer core and the crust Convection currents: the circular currents of heat in the mantle Subduction: the sinking of oceanic crust at a destructive plate margin Collision: the meeting of two plates of continental crust. They are both the same type so they meet 'head on' and buckle Fold mountains: large mountain ranges where rock layers have been crumpled as they have been forced together Ocean trenches: deep sections of the ocean, usually where an oceanic plate is sinking below a continental plate Composite volcano: a steep-sided volcano that is made up of a variety of materials, such as lava and ash Shield volcanoes: a broad volcano that is mostly made up of lava Subsistence: farming to provide food and other resources for the farmer's own family Terraces: steps cut into hillsides to create areas of flat land Irrigation: artificial watering of the land Hydroelectric power: the use of flowing water to turn turbines to generate electricity Natural hazard: an occurrence over which people have little control, which poses a threat to people's lives and possessions. This is different from a natural event as volcanoes can erupt in unpopulated areas without being a hazard Primary effects: the immediate effects of the eruption, caused directly by it Secondary effects: the after-effects that occur as an indirect effect of the eruption on a longer timescale Aid: money, food, training and technology given by richer countries to help poorer ones, either to help with an emergency or to encourage long-term development Earthquake: a sudden and often violent shift in the rocks forming the earth's crust, which is felt at the surface Immediate responses: how people react as the disaster happens and in the immediate aftermath Long-term responses: later reactions that occur in the weeks, months and years after the event Vent: the opening - usually central and single - in a volcano from which magma is emitted Lahar: these secondary effects of a volcanic eruption are mudflows resulting from ash mixing with melting ice or water 26

Supervolcano: a mega colossal volcano that erupts at least 1,000km cubed of ash Caldera: the depression of the supervolcano marking the collapsed magma chamber Fissures: extended openings along a line of weakness that allow magma to escape Geothermal: water that is heated beneath the ground, which comes to the surface in a variety of ways Geyser: a geothermal feature in which water erupts into the air under pressure Hot spot: a section of the earth's crust where plumes of magma rise, weakening the crust, These are away from plate boundaries Focus: the point in the earth's crust where the earthquake originates Richter scale: a logarithmic scale used for measuring earthquakes, based on scientific recordings of the amount of movement Epicentre: the point at the earth's surface directly above the focus Shock waves: seismic waves generated by an earthquake that pass through the earth's crust Mercalli scale: a means of measuring earthquakes by describing and comparing the damage done, on a scale of I to XII Debt: money owed to other, to a bank or to a global organisation such as the world bank The three Ps: the collective term for prediction, protection and preparation Prediction: attempts to forecast an event - where and when it will happen - based upon current knowledge Protection: constructing buildings so that they are safe to live in and will not collapse Preparation: organising activities and drills so that people know what to do in the event of an earthquake Tsunami: a special type of wave where the entire depth of the sea or ocean is set in motion by an event, often an earthquake, which displaces the water above it and creates a huge wave 27