Geography

Plates:- At a CONSTRUCTIVE plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill up the gap. This causes volcanoes. however, since the magma can escape easily at the surface, the volcano does not erupt with much force. e.g. Mid Atlantic Ridge.- At a DESTRUCTIVE plate boundary, the thicker, denser oceanic plate slides beneath the continental plate (subduction). The oceanic plate melts as it reaches the hot mantle. As the plates slide past each other, friction stores energy in rocks and the energy is released in earthquakes, magma may escape and cause volcanoes to occur. The folding of the continental plate forms mountains. e.g. the Nazca plate sub ducts underneath the South American plate.- At a COLLISION plate boundary two plates of similar densities move together, i.e. a continental plate and a continental plate. This causes the material between them to buckle and rise up, forming fold mountains. e.g. The Himalayas formed by the African plate colliding with the Eurasian plate. - At a CONSERVATIVE plate margin, the plates slide horizontally past each other and pressure builds up in the rocks on either side of the fault. The fault surface often rough the friction creates large strains along the faults. An earthquake happens when pressure built up and energy are released in a sudden, jerky movement. e.g the North American plate and Pacific plate.

Active: An active volcano is a volcano which frequently erupts or has erupted within a few thousand years.Dormant: A dormant volcano is inactive, but still expected to erupt.Extinct: An extinct volcano is a volcano that has no records of ever erupting or is not expected to erupt ever again.Magma: Lava: Magma once it reaches the surfaceVolcanic bombs (Ash, steam and gas): Airborne material.Lahars: Mudflows caused by the combination of volcanic materials and water.Pyroclastic flows: Hot gases and steam that flow from a volcano.Case Study - Mount St. Helens:CausesSituated on a destructive plate boundary between the Juan de Fuca plate and the North American plate. When the oceanic plate subducted under the continental plate, which buckled, the friction forced magma out of the crater. EffectsPRIMARY- Nuée Ardente (hot gas and ash) destroyed forests and logging camps. 63 people were killed, mainly by poisonous gases. Lahars covered an extensive area surrounding the volcano.SECONDARY- Ash blocked rivers destroying popular fishing sites and causing flooding. This destroyed crops and livestock. Flooding destroyed communications such as roads and railway bridges. Sediment carried downstream ruined barge transport on the Columbia river. ResponsesSHORT-TERM- Communications such as roads and bridges were repaired. People were rehoused.LONG-TERM- Soil fertility improved due to the ash deposits. The volcano is now more carefully monitored. Tourism has increase, boosting the local economy.Living in tectonically active areas:People may want to live in volcanic areas because:- The weathered lava forms fertile soil.- Tourists are attracted to areas of volcanic activity, e.g. Lanzarote- Geothermal energy can be produced in many volcanic areas, e.g. Geothermal hot springs in Iceland- The dried rock may form minerals which create work in mining.- Picturesque/ scenic views.- Scientists may want to to investigate or study volcanoes.Earthquakes:Seismometer: An instrument to measure the strength of the earthquake.Richter scale: The scale on which the strength of an earthquake is measured.Focus: The place deep in the earth where the rocks are moving.Epicentre: The point at the surface above the focus.Predict- The change in shape of the volcano shows the increased pressure in the magma chamber and the heat.- Gases escaping from the crater of the volcano shows that there is magma building up. There is also a way to check how much gas there is.- Small cracks may start to develop.- There may be small 'fore shocks'.- Most likely after long periods without any plate movement.- Animals often act strangely .Prepare- Organise emergency supplies of water, food and power in advance.- Educate people on what to expect when it will happen.- Disaster plans must be carried out regularly.- Buildings must comply with strict regulations. Protect- Set up an efficient earthquake warning system.- Emergency services must be trained to deal with an earthquake- Safety checks have to be carried out regularly on buildings.- Existing roads, bridges and buildings should be strengthened. Energy:Non-Renewable Energy- Sources of power that will eventually run out.e.g. Coal, Oil, Nuclear, GasRenewable Energy- Sources of power that quickly replenish themselves and can be used again and again. e.g. Solar, Tidal, Wind, HEP, Geothermal

The Structure of the Earth:

Volcanoes:

Development: The state of growth and advancement, e.g. in a countryHow is Development measured?GNP per capita (Gross National Product)- How much money country makes in a yearDevelopment indicators- A development indicator is a measure if the quality of life in a country.HDI (Human Development Index)- The Human Development Index uses three indicators to incorporate social and economical data. These are 'Income per person', 'Literacy rates' and 'Life expectancy' and it is measured using a number from 0 to 1.Are they all useful? - GNP may not be useful because knowing just the income of some people may not mean they are happy.- HPI may not be useful because although we would know the happiness of people in a country, we won't know anything else, i.e. income.- HDI is very useful because it incorporates the 3 main ways to measure development in one result.

Development

Plate tectonics