A2 Geography Plate tectonics

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What are the four layers of the Earth?
Inner core, outer core, mantle, crust
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What are the characteristics of the inner core?
Solid ball, containing lots of iron and nickel.
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What are the characteristics of the outer core?
Semi-molten, containing lots of iron and nickel
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What are the characteristics of the mantle?
Mostly made of silicate rocks. Thick, solid, rocky substance that represents about 85% of the total weight and mass of the Earth.The first 50 miles (80km) of the mantle are believed to consist of very hard, rigid rock. The next 150 miles (241km) or s
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What are the characteristics of the crust?
The rigid top part of the mantle and the crust together are called the Lithosphere. Continental crust is thicker and less dense. Oceanic crust is thinner and more dense.
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What are convection currents?
Lower parts of the asthenosphere heat up (due to radioactive decay), become less dense and slowly rise. They cool down at the top of the asthenosphere, become more dense and slowly sink. This creates drag on the base of the tectonic plates.
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How is crust created?
Rising convection currents diverge at the base of the lithosphere causing the plates to diverge as well. Magma rises and fills the gap.
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What is sea floor spreading?
When convection currents diverge at a plate margin under the sea, the sea floor gets wider. Creates mid-ocean ridges.
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What is the evidence for Continental drift?
South America and Africa fit together like a jigsaw and also have rocks of the same age and composition. By fitting land masses together you can match up the distribution of some fossils. The same living organisms can be found on different continents
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What is Paeleomagnitism?
The study of the history of the Earth's magnetic field. The Earth's magnetic field reverses polarity every 20,000 or so years. As magma erupts from mid-ocean ridges, magnetic minerals align themselves with the direction of the Earths magnetic field.
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What happens at a constructive margin?
Mantle is under pressure from the plates. Plates move apart and pressure is released. This pressure causes the mantle to melt, producing magma. Magma is less dense than the plate above, so it rises and can erupt to form a volcano.
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How do earthquake's form at constructive margins?
The plates don't move apart in a uniform way. This causes pressure to build up. When the pressure becomes too much, the plate cracks, making a fault line and causing an earthquake.
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What happens at oceanic-continental destructive boundaries?
The more dense oceanic crust is subducted under the less dense continental crust forming a deep sea trench.
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How do fold mountains form at destructive boundaries?
Sediments that have accumulated on the continental crust are folded upwards along the edge of the continental crust.
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How are volcanoes formed at oceanic-continetal destructive boundaries?
Oceanic crust is heated by friction and contact with the upper mantle, which melts it into magma. The magma is less dense than the continental crust above and will rise back to the surface to form volcanoes.
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How do Earthquakes form at oceanic-continetal destructive margins?
As one the oceanic plate gets subducted they can get stuck causing pressure to build up. When the pressure becomes too much the plates jerk past each other causing an Earthquake.
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How do Earthquakes and Volcanoes form at oceanic-oceanic destructive boundaries?
The same as oceanic-continental
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Can volcanoes form at a continental-continental destructive boundary?
No, because neither is subducted, but the pressure builds up so Earthquakes can happen?
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What occurs at conservative boundary?
Only Earthquakes
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How are batholiths formed?
When large chambers of magma cool underground they form domes of igneous rocks (batholiths)
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What are dykes and sills?
Where the magma has flowed into gaps in the surrounding rock and cooled it forms vertical dykes and horizontal sills.
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What are cooling cracks?
Cracks may form as the magma cools
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What are the three main types of lava?
Basaltic, andesitic and rhyolitic
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What are the characteristics of Basaltic lava?
Low viscosity, nonviolent eruptions. Frequent, long lasting eruptions.
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What are the characteristics of Andesitic lava?
Medium viscosity and and potential for violent eruptions
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What are the characteristics of Rhyolitic lava?
High viscosity and short lived, intermittent, violent eruptions
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What are the 6 main types of volcano?
Dome, Caldera, Shield, Fissure, Composite, Ash-Cinder
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What are the characteristics of a Dome volcano?
Steep sides (caused by high viscosity lava flowing slowly down the side). Often form at destructive margins. Rhyolitic or andesitic lava. (e.g. Puy de Dome, France)
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What are the characteristics of a Caldera volcano?
Central part has collapsed as magma chamber below has emptied, very wide circular crater. Often occur at destructive margins. Andesitic and rhyolitic lava produced. (e.g. Aira Caldera, Japan)
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What are the characteristics of a shield volcano?
Gentle sloping sides caused by low viscosity lava. Lava erupts from numerous openings. Often occur at constructive margins or hotspots. Usually produce basaltic lava. (e.g. Mauna Loa, Hawaii)
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What are the characteristics of a fissure volcano?
Long, linear vent, can be a few metres wide, but several KM's long. Fairly flat surface caused by low viscosity lava. Often occur at constructive margins and produce basaltic lava (e.g. Laki fissure system, Iceland)
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What are the characteristics of a composite volcano?
Very tall, steep sides, made up of alternating layers of ash and lava.Lava erupts from numerous openings. Usually found at destructive margins. Often produce pyroclastic flows. Usually produce basaltic or andesitic lava. (e.g. Etna, Sicily)
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What are the characteristics of an ash-cinder volcano?
Bowl shaped crater at the summit and steep sides. Not very tall. Formed from cinders (blobs of lava) falling and forming around the edge of the vent.
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What are hot springs?
Where groundwater emerges at the surface. If the groundwater source flows near to an area of recent intrusive activity, it is heated. High mineral content. (e.g. North Island, New Zealand)
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What are geysers?
Groundwater is heated to boiling point by magma deep in the crust. The water becomes pressurised and forces its way to the surface through cracks in the rocks before the hot water and steam spray out from a vent.Erupt periodically.(e.g. Old Faithful)
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What are boiling mud pools?
Another type of hot spring. Form in fine-grained soil areas - hot spring water mixes with the soil to create a hot muddy pool. (e.g. Yellowstone national park)
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What are hotspots?
Occur away from plate boundaries. Caused by a magma plume rising from the mantle. The magma plume never moves, but the crust moves above it, creating a chain of hot spots. (e.g. Hawaii)
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What is the focus of an Earthquake?
The place in the lithosphere where the earthquake starts.
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What is the epicentre of an Earthquake?
The point on the Earths surface where the Earthquake is felt first. Straight above the focus.
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What are the other possible causes of Earthquakes, other than at plate boundaries?
Reactivation of old fault lines, subsidence (when the ground sinks as a result of deep mining), pressure on surface rocks from water in large reservoirs.
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What are the four main types of seismic wave?
P waves, S waves, Love surface waves and Rayleigh surface waves.
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What are P waves?
Travel through the interior of the Earth. Can travel through solids and liquids. Push and pull the Earth in the same direction as the wave is travelling. Fastest of all the seismic waves.
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What are S waves?
Travel through the interior of the Earth. Can travel through solids but not liquids. Move the Earth at 90° to the direction of travel. Cause a lot of damage because of their sheering effect.
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What are Love surface waves?
Can only travel in the crust. Can only travel through solids. Move the surface from side to side. Cause a lot of damage because of their sheeting effect.
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What are Rayleigh surface waves?
Can travel through solids and liquids. Move the surface in a rolling motion (like a wave moving across the ocean)
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How is the magnitude of an Earthquake measured?
Seismometer
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What is the richter scale?
Measures the magnitude of an Earthquake. Doesn't have an upper limit. Logarithmic. Major earthquakes are above 7.
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What is the Mercalli scale?
Measures the impact of an earthquake, measured by observations of the event.
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How are tsunamis formed?
Can be triggered by underwater Earthquakes causing the seabed to moved, displacing water. Waves leave the epicentre. Volcanic eruptions and landslides that slide into the sea can also cause tsunamis. The closer to the shore it starts, the more power.
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What clues are there that an Earthquake may happen?
Small tremors, cracks appearing in rocks, strange animal behaviour, Earthquake warning systems detecting P waves (but only after the quake has begun), data from past Earthquakes can predict where future ones may occur.
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How can volcanic eruption be predicted?
Changes in the shape of the volcano and tiny earthquakes
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How can tsunamis be predicted?
Tsunami warning systems rely on Earthquake detection systems. There are warning centres all around the world.
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How can building techniques physically protect people?
Can be designed to withstand Earthquakes, strengthened so they're less likely to collapse due to the weight of falling ash, use barriers to divert lava flows away, raised open foundations to lessen the impact of a tsunami, tsunami walls.
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What cost effective methods of planning and education are there?
Planning new houses away from area's at most risk. Training emergency services for disasters. Plan evacuation routes (e.g. Leaflets Delivered in Oregon). Educate people on how to evacuate.
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What three main factors effect the severity of a natural hazard?
Development level of a country, population and timing
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What is the name of vulcano which erupted in Montserrat?
Soufriere hills
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When was the Montserrat eruption?
25th June 1997
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What sort of volcano is Soufriere Hills
Composite
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What plate margin is Soufriere Hills at and which plates are these?
Destructive margin. N Amerian plate being subducted under the Caribbean plate.
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How many people died and how many were injured after the Montserrat eruption?
19 died and 7 injured.
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How many of the population left after the eruption of Soufriere Hills?
8,000 of 12,000 (Around 4,00 came to the UK).
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What is the capital of Montserrat and how much much and ash covered it after the eruption?
Plymouth. 12m of Ash.
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What positive point has come from the settling of ash over Montserrat?
It has improved soil fertility
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What help was received after the Montserrat earthquake?
People were evacuated to safe areas in the north. Shelters built. Temporary infrastructure built. Aid from countries including UK. Exclusion zone put in place. Montserrat Volcano observatory set up.
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How much aid did the UK supply Montserrat with after the eruption?
£17 million in emergency aid AND £41 million of long term aid (An oversea's territory of the UK)
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When was the MT. St. Helens eruption?
18th May 1980
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Which state and mountain range is MT. St. Helens in?
Washington. Cascade mountains.
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Which plate margin and plates is MT. St. Helens on?
Destructive margin. Juan de Fuca plate being subducted under N American plate.
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What type of Volcano is MT. St. Helens?
Composite
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What magnitude was the MT. St. Helens earthquake?
5.1
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How many tonnes of ash were deposited after MT. St. Helens?
540 millions tonnes
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What was the total cost of the damage after the MT. St. Helens eruption?
About $1.1billion
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How many people were killed after the MT. St. Helens eruption?
57 (mostly by inhaling volcanic ash)
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How many big game animals were killed after the MT. St. Helens eruption?
Around 7,000
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What responses were there to the MT. St. Helens eruption?
Face masks distributed. Emergency shelters set up. Ash clean-up operations organised. Shipping channels cleared of sediment. 45,500 acres of land replanted. Domsetic water supplies monitored.
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Solid ball, containing lots of iron and nickel.

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Card 4

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Card 5

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