Restless Earth-Case study cards

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  • Created by: DJSalt
  • Created on: 30-03-17 19:23

Layers of the Earth & evidence to support it.

Direct evidence: Mines as they're dug into the Earths crust so we can see the composition of rocks. Direct as it comes from Earth

Indirect evidence: Meteorites, thought to be similar to the Earth's crust. It's indirect as it comes from other planets. 

Lithosphere: 

  • Continental crust, thicker, less dense. Made of granite mostly. 
  • Oceanic crust, thinner, denser, made of igneous mostly. 

Mantle: Partially molten, where the convection currents occur, also called asthenosphere. 

Core:

  • Outer core, liquid, iron and nickel. Between 4000-5000 degrees celsius. 
  • Inner core, solid. over 5000 degrees, thought to be about 5000. 

Remember inner core, outer core, mantle and crust. 

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Convection currents & the Magnetic field

Convection currents:

  • The Earth's core heats the mantle, it's heated by radioactive decay
  • This causes the magma to rise
  • As heat rises it beings to near the surface of the crust, the magma is then forced to move either side and this cause the plates to move due to friction as the magma begins to cool. It begins to cool due to it being further away from the heated area so it falls causing the plate to be dragged with it. The magma sinks back down to be reheated. 
  • These are stong enough to move the tectonic plates on the Earth's surface. 

Plumes: The parts of convection cells where heat moves towards the surface, they bring magma to thr surface. If magma breaks through the crust it erupts as lava in a volcano. 

Magnetic field: The Earth is surrounded by a huge invisble magnetic field called the magnetosphere. It's a force field, protects the Earth from harmful radiation from space and the sun. It's made by the outer core . As liquid iron in the outer core flows, it works like an electrical dynamo producing a magnetic field. 

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Plate boundaries

Destructive boundaries: 

  • Example; Nazca oceanic plate is subducted (the tramsformation into magma of a denser ectonic plate as it dives under another less-dense plate)under the South American continental plate
  • As plates push together the oceanic plate is subducted. As it sinks it melts and makes magma. As the plate is subducted into the mantle it's subjected to increased pressure and temperature
  • Sea water is also dragged down with it causing the magma to become less dense it then rises to the surface to form volcanoes. The oceanic plate is aslo melted in the mantle. Old crust is destroyed here. 
  • The oceanic plate can stick to the continental plate. Pressure then builds up against the friction. When the plates finally snap apart a lot of energy is released as an earthquake. Tsunamis can form when this happens.

Constructive boundaries: 

  • Convection currents cause plates move apart (usually between two oceanic crusts), magma rises through the gap. New crust is created here. Eurasian plate and the North American plate. Also form ridges when magma seeps out (example would be Mid-Atlantic ridge. 
  • Magma is very hot and runny, flows for a distance and then forms a shallow sided volcano. 
  • Earthquakes caused by friction as plates tear apart.                                                                                               Epicentre: Point on the earths surface directly above the focus where the earthquake hits                                             Focus: The place in the earths crust where the earthquake happens
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Plate boundaries continued

Conservative boundaries:

  • Example is the San Andreas fault in California, USA. Destructive earthquake can happen here and they are up to 8.5 in magnitude. No volcanoes form here. (usually between two continental plates, can occur between any though)
  • As plates slide past each other friction between them causes earthquakes. 
  • Large earthquakes are rare but destructive as they are close to the surface. 

Collision zones: 

  • Type of destructive boundary, form mountain ranges like the Himalayas. Two continental plates of low-density granite collide, pushing up mountains (fold mountains). Earthquakes happen on faults

Fold mountains: 

  • Two continental plates collide.
  • The low density crstal material cannot be subducted
  • Due to this it's crushed and crumpled. This pushes up material forming fold mountains. 

Hotspots: an area where plumes of magma rise to the surface although not close to a plate boundary

Faults: The fractured surface in the Earth's crust (where Earthquakes happen most)

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Tsunamis

Tsunamis:

They are caused when earthquakes occur, particularly at destructive plate boundaries due to the magnitude. A fault can cause the seabed to joly upward from an earthquake, the water is then forced upwards and the tsunami waves spread out in all directions. The seabed becomes shallower closer to the coast, the tsunami waves slow down an wavelength drops but wave height increases dramatically. 

They travel up to 900 km/h with wavelengths of over 200km. As the waves approach the coast they slow down, bunch up and the wave height increases up to 30m compared with 1m when in open ocean. 

When the tsunami hits they cause a very powerful flood, pushing several kilometers inland and destroying homes, bridges and infrastructure.

Warning systems in the ocean can detect tsunami and set off sires and alarms, only useful if the epicentre is some distance from the coast. 

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Kobe, Japan 1995

The Kobe Earthquake

The Kobe Earthquake occured in Japan, 1995. It had a magnitude of 7.2. The focus was 16km deep on the fault. 

Primary impacts:

  • 5000 people were killed
  • 26,000 people were injred.
  • Population denisty is very high and people were still in bed when it struck. Bridges and roads collapsed, train lines damaged. 
  • £100 billion of damage caused to roads, houses, factories and infrastructure.

Secondary impacts:

  • Many fire sbroke out throughout the city, triggered by broken gas pipes resulting in further deaths.
  • Businesses were affected for many weeks due to disruption caused by rebuilding.
  • Homelessness, disrupted schooling, unemployment last for many months as hard to cope.
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Hazard design buildings in the developed world

Japan is a developed country so it can afford to build buildings resistant to earthquakes. They aslo have other methods of keeping people safe:

  • Every year Japan has earthquake drills
  • Emergency services practise rescuing people
  • People keep emergency kits at home containing water, food a torch and radio

They also have buildings designed to resist these hazards:

  • A damper in the roof acts like a pendulum reducing building sway
  • Cross bracing stops floor collapsing
  • Shock absorbers built into cross braces
  • Strong steel frame whcih is also flexible, stops cracking
  • Strong double glazed windows stop broken glass showering down
  • Very deep foundations to prevent collapse
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Port-au-Prince, Haiti 2010

Port-au-Prince, Haiti Earthquake

The earthquake happened in 2010 and had a magnitude of 7.0. Focus 13km deep on a conservative plate boundary. It struck at 5p.m.

Primary impacts:

  • 316,000 deaths
  • 300,000 people were injured
  • Total economic loss of £8.5 billion
  • Poverty and slum housing caused building collapsing.
  • 1 million people made homeless

Secondary impacts:

  • Over 7000 people killed due to things such as cholera
  • Damage to roads and ports stopped trade
  • Cholera spread due to lack of clean water and sanitation. 
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Port-au-Prince Haiti 2010-Relief effort

The relief effort:

The government and international countries tried to respond to the earthquake in different way:

  • They used excavation teams to clear rubble and look for suvivors
  • UN's world food programme flew in two planes with emergency food aid
  • World vision, an NGO provided food for 1.2 million, emergency shelter for 41,000, delivered 16 million litres of clean water, ran health and education, childhood and livelihood programmes.
  • The Inter-American Development Bank immediately approved a $200,000 grant for emergency aid
  • President Obama promised $100 million in Aid.

The Analysis:

Haiti is a very poor country so most help provided was from charities and NGOs, not from governments. The country is also controlled by a tiny elite who may not get aid to the right people. Even in 2012, Haiti was still trying to recover. 

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Hazard design buildings in the developing world

As developing countries cannot afford the hazard design availabe in the developing world they ensure if their homes do collapse due to an eartquake they will not die. Some of these include:

  • Cross-braced wood or bamboo frame
  • Concrete ring ties the walls to the foundations
  • Simple steel rod foundations 
  • Lightweight thatch roof, if it does collapse it will not kill
  • Walls made of mud and sraw packed between wooden slats (won't get stuck in the house)
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Sakurajima, Japan

Sakurajima Japan

The area:

  • 40% of land is fertile volcanic soil growing tea and rice
  • Lots of urban areas around the bay
  • 7000 people live at the base of the volcano
  • Hotsprings and lava flows are a popular tourist resort
  • The sheltered bay makes a good port and fishing is an important industry
  • Kagoshima has a population of 650,000, big eruption could easily devastate it with ash, lava bombs and pyroclastic flows.

Japan is a developed country meaning it can manage the impacts by evacuating and setting up equipment; for example: (Next card)

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How to detect volcanoes:

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Mount Nyiragongo-Democratic Republic of Congo-2002

In January 2002 a fast flowing river of basalt lava poured out of Mount Nyiragongo and into the city of Goma. 

Social impacts:

  • 12,500 homes destroyed by lava flows and earthquakes
  • 100 people died
  • 400,000 people were evacuated to refugee camps
  • Disruption to the mains water supplies caused concern for the spread of diseases.
  • 120,000 made homeless

Economic impacts:

  • Poisonous gases caused acid rain, affected farmland and cattle - many farmers lost income
  • Due to poverty, most people could not afford to rebuild their homes

This was a crisis and people needed help quickly, due to this a relief effort was established:

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Mount Nyiragongo-Democratic Republic of Congo-2002

Relief effort:Little clean water, food and shelter, cholera could spread. The UN and Oxfam began a relief effort to help:

  • UN sent in 260 tonnes of food in the first week. Families got 26kg of rations
  • In the UK, TV appeal asked people to give money in order to help.
  • Government around the world gave $35 million to get aid to the refugees
  • Emergency measles vaccinations were carried out by the World Heath Organisation. 

Most people fled from the lava with nothing due to poverty. Months before many could start building new homes. By June 2002 some roads had been cleared of lava and the water supply repaired.

Also volcanic activity under Lake Kivu. Gases like carbon dioxide and sulfur dioxide rise through the Earth into the lake. They get trapped in mud on the lake bottom. An earthuqake could shake these gases free which would cause many to suffocate

There is also an airport and any income from tourism during this time would be stopped as people would not visit due to the volcanic eruption. 

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