Inside the Earth
- The Earth's core generates heat through radioactive decay and convection currents move plates.
- Lithosphere: consists of the crust (oceanic and continental) and a brittle part of the solid upper mantle. It is split up into tectonic plates
Oceanic Crust: Mainly under the oceans. Basaltic rock which is constantly being destroyed and renewed Denser than continental crust so it SUBDUCTS underneath continental crust 6-8km thick on average
Continental Crust: Forms on the land Made of mostly ganite and it is permanent It has a low density 30-1000km thick on average
Asthenosphere: The lubricationg layer under the litoshpere, where the tectonic plates move on. It is made up of dense, partly molten rock so that the plates don't sink. It is part of the MANTLE
Inside the Earth .2 Mantle & Core
The Lower Mantle: The largest of the Earth's layers by volume and it is mostly solid.
- Inner Core: It always stays solid because it is very deep and is under huge amounts of pressure.
- Outer Core: It is liquid because it is under lower pressure. Convection currents in the outer core causes the magnetosphere ( a magnetic force field). The magnetosphere acts as a shield against harmful radiation and cosmic rays.
The geothermal heat from inside the Earth is produced by the radioactive decay of uranium raising the core's temperature to over 5000 degrees.
- The geothermal heat from radioactive decay rises from the core and creates convection currents in the liquid outer core and the mantle. These currents move the plates 1-2cm a year
- The parts of convection currents where heat moves towards the surface are called plumes.
The lithosphere is split into 15 large tectonic plates and over 10 small ones, which move very slowly on top of the asthenosphere. The place where two plates meet is caled a plate boundary.
Constructive Plate Boundary:
- Where two oceanic plates are moving apart from eachother.
- Convection currents form the mantle bring magma owards the surface. Magma is forced between the plates, cools and forms new oceanic crust.
- The magma is non-viscous (runny). Shallow sided SHIELD volcanoes form.
- Small earthquakes are formed by friction as the plates tear apart.
- Volcanoes that are not very explosive/dangerous form e.g. Iceland - Mid Atlantic Ridge
Plate Tectonics .2
Destructive Plate Boundary:
- Where an oceanic plate meets a continental plate. The denser oceanic plate is subducted beneath the less dense continental plate. The oceanc plate meles as it subducts into the mantle, which creates magma.
- Very destructive earthquakes ( up to 9.5 on the Richter scale) e.g. Japan
- Tsunamis can form as a secondary hazard
- Very explosive, destructive volcanoes can form that cool to steep sided.
- Volcanoes erupt andesitic (high viscosity) lava which is explosive e.g. Andes Mtns Peru, Chile
- A type of destructive boundary where two continental plates move towards eachother. As they meet, they push upwards forming mountain ranges e.g. Himalayas.
Plate Tectonics .3
COLLISION ZONE HAZARDS
- destructive earthquakes up to 9.0 on the Richter scale
- landslides are triggered
- volcanoes are rare
Conservative plate boundary
- Formed where two plates are sliding past eachother. e.g. San Andreas Fault, California & Haiti
- Destructive earthquakes up to 8.5 on the Richter scale e.g. Haiti
- Small earth tremors occur almost daily
- No volcanoes occur
Tectonic Hazards: Volcanoes
Volcanoes are found on the edge of plate margins e.g. subduction zones such as the Pacific Ring of Fire. They are also found at constructive margins e.g.Mid-Atlantic Ridge and at hotdpots e,g, Hawaiian Islands.
- It is the viscosity of the magma that largely determines the nature and power of an eruption and the resultant shape of the volcano. The more viscous the magma/lava is then the steeper the volcano and the more explosive it is.
Types of volcanoes and main features
- Shield volcanoes are usually found at constructive boundaries.
- Gentle sloped and a wide base of mainly lava.
- Frequent eruptions of non-viscous basic lava which are usually not explosive e.g. Hotsopts; Mauna Loa, Hawaii
Tectonic Hazards: Volcanoes 2
Composite/ Strato Volcanoes
- They are usually found at destructive boundaries.
- They are steep sided with a distinctive cone shape.
- Explosive eruptions of viscous and thick lava occur- so the lava doesn't travel far.
- They can produce layers of alternating ash and lava e.g. Sakurajima, Japan
- Non-explosive eruptions tend to produce mostly lava flows. It is only when large quantities of very fluid lava are present that it is a real danger to people e.g. Mt Nyiragongo, The Congo
- Ash clouds- explosive eruptions blast solid and molten rock fragments into the air with tremendous force.e.g. Icelandic Volcano
- Pyroclastic flows- these are cloudsof gas, ash, and rocks often reaching temperatures up to 800C and travelling at speeds up to 200kph down the sides of the volcano
- Lahars- these are cement like mudflows consisting of volcanic ash and water.
Case Study:Mt Nyiragongo, Composite Volcano 2002
Causes: A constructive plate boundary where the African Rift Valley is moving apart.
- Much of the local cities (Goma), infrastructure e.g. roads, and the airport were destroyed by the lava, which was up to 3m thick in some places.
- 12,500 homes and business premises were demolished by the lava and 14 villages were destroyed.
- 100 people lost their lives, mostly from poisonous gas and getting trapped in lava.
- Some 500,000 residents of Goma fled the city; many became short term refugees in neighbouring Rwanda.
- With little clean water, food and shelter, diseases like cholera spread
- Goma airport was destroyed by the river of lava, which slowed down aid distribution.
Case Study .2 & Impact on Developing Countries
- The United Nations and Oxfam began a relief effort to help, this aid included; 260 tonnes of food in the first week. Governments arounds around the world gave US $35 million to get aid to the refugees.
- Emergency measles vaccinations were carried out by the World Health Organisation.
- 6 months after the volcanic eruption some roads had been cleared of lava and the water supply was repaired.
Why do volcanoes have a severe impact on Developing countries?
- Many people live in dangerous areas as they are poor and do not have other choices. Many live in poverty and can't afford well-built houses so they often collapse. When Mt Nyiragongo erupted in 2002 at least 15% of the nearby town of Goma's 4,500 buildings were destroyed leaving about 120,000 people homeless.
- Most people may not have insurance so they may lose their homes and fields.
- Governments may not have the resources to provide aid in terms of food, water and evacuation shelters. There isnt good communication (roads, airports) so aid relief found access hard
Why people live near volcanoes/Managing Volcanoes
- Fertlie volcanic soil for farming.
- Hot springs and lava flows are a tourist attraction
Managing the volcanic hazard
- Scientists monitor the telltale signs that precede a volcanic eruption- lots of tiny earthqakes, rising magma, escaping gas, increased magma temperature and chages in tilt (bulge) of volcano sides. People can be warned and lives saved by evacuation.
- Channels can be dug to re-direct lahars away from settlemets e.g. Sakurajima, Japan
- Concrete shelters to protect against volcanic bombs and ash from pyroclastic flows
- Evacuation routes and regular drills so people know what to do if an erutpion occurs.e.g Sakurajima, Japan
- Construction rules to ensure buildings can take the weight of ash deposits
- Landuse zoning restricting access to the most dangerous locations e.g. Montserrat
Tectonic Hazards: Earthquakes
These are located along plate margins where plates are subducted e.g Japan or collide e.g. China or at conservative margins e.g Haiti
- Earthquakes are sudden releases of pressure that has been built up as tectonic plates move into, over or past eachother, depending on the boundary type. The pressure is suddenly released at faults (cracks in the crust) as huge pulses of energy.
- A seismograph measures the magnitude of an earthquake
- Earthquakes that have a shallow focus or hypocentre (the place in the crust where the earthquake takes place) are closer to the epicentre (surface of the earth directly above the focus) and will therefore be more destructive thanan earthquake with a deep focus.
Why do some earthquakes cause more damage?
- Emergency services may be poorly equipped in some countries making it difficult to reach people trapped under poorly constructed buildings.
- Construction laws are less strict in some countries leading to buildings which quickly collapse when tremors hit so destroying buildings and killing people.
Case Study: Haiti Earthquake 2012
- The epicentre was 25km from the densely populated capital of Port-au-Prince (2.5 million people). Nearly 1 million people live in poorly constructed, densely populated shanty towns which collapsed easily.
- Haiti is a poor developing country and there were few emergency services (fire, ambulance, police) to deal with rescuing and treating survivors so Haiti had a low capacity to cope with the earthquake disaster.
- Haiti had a weak government and very little money to spend on education and making buildings aseismic, not even public buildings like schools and hospitals were made aseismic.
- High magnitude of 7.0 on the Richter scale so the amount of shaking was worse so there was more damage to buildings resulting in more deaths.
- The earthquake had a shallow focus so the seismic waves were worse.
Case Study .2 Primary Effects/Immediate Response
- About 200,000 people were killed and 300,000 injured.
- The major port was badly damaged, along with many roads that were blocked by fallen buildings and smashed vehicles.
- Eight hospitals or health centres in Port-au-Prince collapsed, or were badly damaged.
- Many government buildings were also destroyed.
- About 100,000 houses were destroyed and 200,000 damaged in Port-au-Prince and the surrounding area. Around 1.3 million Haitians were displaced (left homeless).
Immediate Response & Relief
- Haiti had a low capacity to cope and so relief and aid was slow. There were few emergency services to clear the roads and rescue survivors. So Haiti relied on foreign support (aid) especially from the US. Local people dug out survivors with their bare hands.
- Because the main port and roads in Port-au-Prince were badly damaged, crucial aid (such as medical supplies and food) was slow to arrive and be distributed. American engineers eventually cleared the port and airport, so that waiting ships could unload aid. Bottled water and water purification tablets were provided to surviovirs. Field hospitals were set up and helicopters flew wounded people to nearby countries.
Case Study.3 Secondary Effects/Longer-term Respons
- Over 2 million Haitians were left without food and water. Looting became a serious problem.
- The destruction of many government buildings hindered the government's efforts to control Haiti and the police force collapsed.
- The damage to the port and main roads meant critical aid for immediate help and long-term reconstruction were prevented from arriving, or being distributed effectively.
- Displaced people moved into tents and temporary shelters, and there were concerns about outbreakes of disease. By November 2010, there were outbreaks of cholera in the camp and 4000 people died. Even 2 years later 500,000 people were still living in refugee camps.
- Stress caused by loss of family, homes and businesses. As Haiti is a developing country, the secondary impacts were severe and even three years after the earthquake the city still has large areas of collapsed buildings/rubble