Tectonic activity – TheessentialsTectonic activity – Theessentials
The earth’s crust is made of huge floating plates (rock).
The earth is like a broken egg shell. These plates float on the
mantle (molten material) in different directions a few
cm/year. Plates meet at plate boundaries or margins
There are 3 different types of plate margin:
1.Constructive
2.Destructive
3.Conservative
World map showing plate boundaries and theirmovement
2 plates move away from one another. Magma risesfrom the mantle. New crust is created. Volcanoes getformed.
At a destructive boundary the plates are moving towards each other. This tends toinvolve a continental plate (a plate carrying land) and an oceanic plate (a platecarrying ocean).
The oceanic plate is denser than the continental plate so, as they move together, theoceanic plate is forced underneath the continental plate. The point at which thishappens is called the subduction zone. As the oceanic plate is forced below thecontinental plate it melts to form magma. The magma collects to form a magmachamber. This magma then rises up through cracks in the continental crust. Aspressure builds up, a volcanic eruption may occur.
At a conservative boundary the plates are sliding horizontally past each other.No land is created at a conservative boundary and none is destroyed.
Volcanoes do not occur along these boundaries but earthquakes are verycommon. A very well-known example of a conservative boundary is the SanAndreas Fault, which runs through the state of California in the USA.
How are fold mountainsformed? (destructive margin)How are fold mountainsformed? (destructive margin)
Fold mountains e.g. Alps, Rockies, Himalayas are formed when twoplates move together (a destructive plate margin). This can be wheretwo continental plates move towards each other or a continental and anoceanic plate.
The movement of the two plates forces sedimentary rocks upwards intoa series of folds. Fold mountains are usually formed from sedimentaryrocks. When plates and the continents riding on them collide, theaccumulated layers of rock crumple and fold like a tablecloth that ispushed across a table.
Case study fold mountains: TheAndes – how do people use them?Case study fold mountains: TheAndes – how do people use them?
FARMING – subsistence farming occurs on steep slopes e.g.potatoes. Terraces (steps cut into hillsides to create areas of flat land)retain water and limit soil erosion. Most crops are grown in the valleyse.g. rice, cotton, soy beans. Llamas are use as pack animals (mainlymales carrying equipment) and the females are used for milk and meatand wool is used in clothes and rugs.FARMING – subsistence farming occurs on steep slopes e.g.potatoes. Terraces (steps cut into hillsides to create areas of flat land)retain water and limit soil erosion. Most crops are grown in the valleyse.g. rice, cotton, soy beans. Llamas are use as pack animals (mainlymales carrying equipment) and the females are used for milk and meatand wool is used in clothes and rugs.
MINING – Andean countries are important for tin, nickel, silver andgold mining. Towns grow as a result of job creation. However, this bringsan increased crime rate.MINING – Andean countries are important for tin, nickel, silver andgold mining. Towns grow as a result of job creation. However, this bringsan increased crime rate.
HEP (Hydroelectric power). Steep slopes and narrow valleys can easilybe dammed; there is lots of precipitation and spring melt snow togenerate electricityHEP (Hydroelectric power). Steep slopes and narrow valleys can easilybe dammed; there is lots of precipitation and spring melt snow togenerate electricity
TOURISM – There are many natural attractions e.g. mountains,volcanoes, glaciers and lakes. Some people follow the Inca trail (ancientpeople) to see famous early settlements e.g. Machu PicchuTOURISM – There are many natural attractions e.g. mountains,volcanoes, glaciers and lakes. Some people follow the Inca trail (ancientpeople) to see famous early settlements e.g. Machu Picchu
World map showing the distribution of volcanoes(spread of)
A cross section of a volcano and its features
Composite Volcano
shield volcanoThe shape of a volcano depends on the type of magma and the kind of vent out ofwhich the lava comes. If very runny magma erupts, the lava spreads out quickly toform a low, gently sloping shield volcano e.g. Mauna Loa, Hawaii.
composite volcanoIf a vent becomes blocked, smaller vents often break out around it (throughcracks/weaknesses in the rock) and form small cones on the side of the main one(secondary). This is called a composite volcano. When thick sticky magma eruptsthrough a central vent, the lava forms a steeper sided cone.
Cause/effects Montserrat eruption 1995-8Cause/effects Montserrat eruption 1995-8
Cause:Cause:
Destructive plate margin – Caribbean plate NorthAmerican Plate (subducted, Destructive plate margin – Caribbean plate moves towards and underneath the NorthAmerican Plate (gets subducted, as it is oceanic crust i.e. is heavier)
EffectsEffects
Primary:Primary:
2/3 of the island was covered in ash
50% of the population were evacuatedto the north of the island to live inmakeshift shelters
23 people died in 1997
Plymouth - the capital was evacuated
The airport and port were closed
Farmland was destroyed
Many schools and hospitals weredestroyed
EffectsEffects
Secondary:Secondary:
Floods as valleys were blocked with ash
Forest fires caused by pyroclastic flows
As most of the southern area was destroyedany remaining inhabitants have had to endureharsh living conditions in the North.
Transport remains a problem for peopletravelling to the island as the port and airportremain closed.
The tourist industry is still suffering with fewvisitors except for cruise ships looking at thevolcano
Over half the population left the island and havenot returned
Immediate/long term responses Montserrateruption 1995-8Immediate/long term responses Montserrateruption 1995-8
Immediate:Immediate:
Farmers quickly collected what harvest they could as first eruptions happenedFarmers quickly collected what harvest they could as first eruptions happened
Inhabitants nearby were evacuated to a ‘safe zone’ in the northInhabitants nearby were evacuated to a ‘safe zone’ in the north
Long term:Long term:
£41 million was given in aid by the British Government.£41 million was given in aid by the British Government.
Money was given to individuals to help them move to other countries (7000 left).Money was given to individuals to help them move to other countries (7000 left).
Riots occurred as locals complained that the British were not doing enough to helpthe islandRiots occurred as locals complained that the British were not doing enough to helpthe island
The MVO (Montserrat Volcano Observatory) was set up to study the volcano andprovide warnings for the futureThe MVO (Montserrat Volcano Observatory) was set up to study the volcano andprovide warnings for the future
A Risk assessment was done to help islanders understand which areas are at riskand reduce problems for the future.A Risk assessment was done to help islanders understand which areas are at riskand reduce problems for the future.
Monitoring and predicting eruptionsMonitoring and predicting eruptions
How can you predict and monitor volcanic eruptions?
1.Earthquakes are a sign of an impending eruption
2.‘Swelling’ (magma building up) on the sides of a volcano
3.Tiltmeters detect a change in slope caused by shiftingmagma under the rock surface
4.Global positioning systems (GPS) use satellites todetect movement as little as 1mm
5.Digital cameras on the edge of craters allowvolcanologists to make safe observations
6.Changing gases escaping from a vent are a sign of animminent eruption. Tiny robots called ‘spiders’ are nowused to collect samples.
SupervolcanoesSupervolcanoes
What is one?
A supervolcano is a mega colossal volcano that has the capacity to erupt a 1000times more material (ash, lava) than a normal volcano.
What are its characteristics?
Much wider and less steep than normal volcano
Much bigger scale, emitting far more material than a normal volcano (1,000kmcubed, instead of 1km cubed)
They have large depressions (calderas – a collapsed magma chamber) insteadof a cone shape)
What are the likely effects of an eruption?
The effects could be global e.g. dramatically affecting climate as an ash cloudcould reduce incoming solar radiation (small ice age?)
A huge area of land could be covered, resulting in crops failing, huge airtransport problems and thousands of people dying
World map showing the distribution ofearthquakes (spread of)
A cross section of an earthquake andrelated features
Key terms - earthquakesKey terms - earthquakes
Epicentre – the point on the earth’s surface directly above the focus
Focus – the point in the earth’s crust where the earthquake happens
Shock waves – seismic waves generated by the earthquake, whichpass through the earth’s crust
Richter Scale – logarithmic scale (each increase in 1 means a 10 foldincrease in energy) which measures the strength of an earthquake.There is no upper limit
Mercalli Scale – a means of measuring earthquakes by describing andcomparing damage done on a scale of 1 to 12.
Case study (MEDC):Kobe Earthquake, Japan 1995Case study (MEDC):Kobe Earthquake, Japan 1995
CauseCause
Kobe is near a destructive plate margin where the Pacific Plate (oceaniccrust) gets subducted (forced underneath) below the Eurasian Plate(continental crust) as it is heavier.
EffectsEffects
Primary:Primary:
Nearly 200,000 building s collapsed and roads are destroyed e.g.Hanshin elevated highway
Many bridges collapsed along 130km section of bullet train route
120 of 150 quays in the port are destroyed
Secondary:
Water pipes and gas mains burst. Electricity supplies disrupted
Wall of fire up to 500m wide sweeps city (caused by broken gas pipesand ruptured electricity mains)
5,500 people killed; 40,000 injured; 180,000 houses destroyed
230,000 homeless – living in temporary shelters. Shortage of blankets,clean water and food)
Major industries forced to close e.g. Panasonic and Mitsubishi
10 trains derailed
Temples destroyed in nearby Kyoto
Responses
Immediate:
Friends and neighbours, joined by emergency services searched through rubble
Hospitals struggled to cope, treating people in corridors
Major retailers e.g. 7-Eleven, helped provide essentials e.g. food
Motorola gave people telephone connections free of charge
Railways were 80% operational within a month
Long term:
• Infrastructure e.g. water, gas, electricity and phone services were fully operationalby July 1995
• All rail services back to normal by August
• Within a year, the port was 80% operational
• Rubber blocks were put under bridges to absorb shocks
• New buildings were built further apart (to prevent domino effect) and with flexiblesteel frames
Case study (LEDC):The Sichuan Earthquake, China, 2008Case study (LEDC):The Sichuan Earthquake, China, 2008
Cause
The pressure resulting from the Indian Plate colliding with the EurasianPlate, was released on 12th May 2008, leading to an earthquakemeasuring 7.9 on the Richter Scale.
Effects
Immediate:
55,000 reported dead within 11 days and 18,000 missing
374,000 injured
5 million homeless
In rural areas, 80% of buildings collapsed
5 million buildings collapsed, including a number of schools (one had 900pupils which were killed).
Communications (land and mobile phones) were cut and roads wereblocked by landslides
Long term:
2 months later, 69,000 are confirmed dead
Landslides blocked rivers, leading to fears of flooding
Responses
Immediate:
• 20 helicopters are sent to help by Chinese Government
• Troops parachute in to assess situation and 1000s of army troops help onthe ground
• Rescue workers search for trapped survivors
• Land flattened to put up tents to shelter people from spring rains
• Teams from Japan, South Korea and Russia help rescue effort
• Donations to Red Cross exceed £100 million, much being spent on food,medicine, doctors, volunteers, tents, mattresses and blankets
Long term:
• 1 million temporary small homes are built for homeless
• Chinese Government pledges $10 million rebuilding fund
• Banks write off debts owed by survivors without insurance
Prediction, protection and preparation
The 3 Ps are the key to reducing the impact of earthquakes:
PREDICTION – This involves trying to forecast when an earthquakewill happen by: monitoring foreshocks (although their usefulness islimited if you want to evacuate an area); animal behaviour has beenused but is sceptically viewed by many.
PROTECTION – Building to an appropriate standard and usingdesigns to withstand movement is the main form of protecting people.Buildings can have: an interlocking steel frame which can swing duringearth movements; an automatic window shutting system to preventfalling glass; rubber shock absorbers at base (built into foundations);fire resistant building materials.
PREPARATION – Involves hospitals, emergency services and peoplepractising for disasters e.g. drills/code of practice, so people knowwhat to do to increase their chance of surviving.
Case Study of a tsunami:SE Asia, Boxing Day 2004
Cause
On 26th December 2004, an earthquake (10km below the sea bed, 150miles off the coast of the island of Sumatra, Indonesia) measuring 9.1 onthe Richter Scale happened at 7.59am local time (12.59am GMT).
The earthquake was caused by the Indo-Australian Plate subducting(being forced underneath) beneath the Eurasian Plate.
Effects
Estimates suggested more than 220,000 died, 650,000 were injured and 2million made homeless as a result of tsunami waves, up to 25 metres highcoming ashore in different countries. Public buildings e.g. hospitals andschools were wiped out in some areas. Up to 1,500 settlements werecompletely destroyed in the province of Banda Aceh, Indonesia.
Map showingcountriesaffected
Responses
Rescue services and emergency teams were swamped by the scale ofthe disaster.
Bodies littered the streets before being buried in mass graves.
International Aid poured in e.g. fresh water, water purification tablets,food, sheets and tents. Medical teams and forensic scientists arrived.
UK government promised £75 million and public donated £372 million.
There were organisational issues following the collection of large sumsof money but it has been spent on rebuilding projects in Sri Lanka andIndonesia.
A tsunami warning system was set up in 2006 around the Indian Oceanto ensure that people know how to respond and that local authorities haveplans in place in case a tsunami happens again.
Useful websites - animationsUseful websites - animations
http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundaryrev3.shtml (destructive/compressional plate boundaries)
http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundaryrev2.shtml (constructive/tensional plate boundaries)
http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundaryrev4.shtml (conservative/lateral plate boundaries)