↳ The crust is divided into tectonic plates – they are made of continental and oceanic plates.
↳Continental – thicker and less dense.
↳Oceanic – thinner and more dense.
↳ Destructive – two plates are moving towards each other.
· Where an oceanic plate meets a continental plate, the denser oceanic plate is forced into the mantle and destroyed – this creates volcanoes in the ocean trench.
· Where two continental plates meet and they smash together, but no crust is destroyed.
↳ Constructive – two plates moving away from each other.
· The magma rises from the mantle which fills the gap and cools therefore, creating a new crust.
↳ Conservative – two plates are moving sideways or past each other.
· The crust isn’t created nor destroyed.
↳ When tectonic plates collide, the sedimentary rocks are forced upwards to form mountains.
↳ Therefore, fold mountains are found at destructive plate margins.
↳ You can also get fold mountain where a continental and oceanic plate collide. (The Andes, South America)
↳ You can also get fold mountains where two continental plates collide. (The Himalayas, Asia)
CASE STUDY – ALPS
Location – Central Europe (Austria, France, Germany, Italy, Liechtenstein, Slovenia and Switzerland).
Formation – By collision between the African and European plates.
The Alps are used for:
· Steep uplands are used for: farming goats which provide milk, cheese and meat.
· To plant vineyards (Lavaux, Switzerland)
↳ Hydro-Electric Power (HEP)
· Narrow valleys = dammed = generate HEP. (Berne, Switzerland)
· Electricity produced for locals, powering homes and businesses. Also, exported to towns and cities further away.
· 100 million + tourists visit The Alps a year.
· 70% visit steep, snow covered mountains for extreme sport (skiing, snowboarding ect)
· Villages are built for tourists (Tigenes, France)
· Scots Pine is planted all over the Alps which make it more resilient to goats and also, the trees are logged and sold to make furniture.
CASE STUDY – ALPS (Continued...)
People have also adapted to the conditions in the Alps:
↳ Steep relief
· The goats are farmed as they are well adapted to steep mountains. Also, the trees and any other man-made defences are used to protect against avalanches.
↳ Poor soils
· The animals are grazes in high areas due to the fact that the soil isn’t as capable for growing crops.
↳ Limited communication
· Roads have been built at lower points of the mountains. (The Brenner Pass between Austria and Italy)
↳ Composite volcanoes (Mt. Fuji, Japan):
· This is made of lava and ash which has erupted over the years and is cooled and hardened down to form layers.
· The lava is thick and flows slowly therefore, it hardens quickly resulting to form a sleep-sided volcano.
↳ Shield volcanoes (Mauna Loa, Hawaii):
· This is made up of only lava.
· The lava is runny; therefore it flows quickly and spreads over a wide area hence forming a low, flat volcano.
↳ Dome volcanoes (Mt. Pelée, the Caribbean):
· This is also only made of lava.
· The lava is thick therefore, it flows slowly and hardens quickly and so, it forms into a steep-sided volcano.
CASE STUDY – SOUFRIÈRE HILLS, MONTSERRAT
Date of eruption – 25th June 1997
Size of eruption – 4-5 million m3 of rocks and gas released
Death toll – 19 killed
Cause – the Atlantic plate was forced under the Caribbean plate
↳ Primary impacts:
· Large areas were covered with volcanic material.
· Over 20 villages and about two thirds of homes were destroyed by the pyroclastic flows.
· Schools, hospitals, the airport and port were destroyed.
↳ Secondary impacts:
· Fires destroyed many building such as government offices and police headquarters.
· There was a population decline – 8,000 of the 12,000 inhabitants left.
· Volcanic ash improved soil fertility
CASE STUDY – SOUFRIÈRE HILLS, MONTSERRAT (Continue
↳ Immediate response:
· People evacuated from the south area to safe areas in the north.
· Temporary infrastructure was built
· Shelters were built to house evacuees
↳ Long-term response:
· A risk map was created.
· The south of the island is off-limits as it is still active.
· The Montserrat Volcano Observatory has been set up and tries to predict future eruptions.
↳ The magma rises up through cracks in the crust which form a magma basin below the surface. So, the pressure of the magma causes a circular bulge on the surface.
↳ Then, the bulge eventually cracks which creates vents for lava to escape through resulting the lava to erupt out of the vents which causes earthquakes
↳ The magma basin empties and the bulge is no longer supported therefore, this causes more lava to spew as the bulge has collapsed.
↳ When the eruption is finished, a caldera is left – these often form large lakes.
A super volcano:
↳ Is flat.
↳ They cover a large surface area.
↳ They have a caldera.
The possible consequences if a super volcano erupts:
↳ A thick cloud of gas and ash will form burning and burying everything in its path.
↳ It would trigger mini ice ages as the ash will block out daylight.
↳ The ash will settle over large areas burying fields and buildings.
Earthquakes occur at all three types of plate margins.
↳ Destructive margins
· Tension is built when one plate gets stuck as it’s moving down past the other into the mantle.
↳ Constructive margins
· Tension is built along cracks within the plates as they move away from each other.
↳ Conservative margins
· Tension is built when the plates which are grinding past each other gets stuck.
Earthquakes can be measured by using:
· The Richter Scale
· The Mercalli Scale
CASE STUDY – EARTHQUAKES
CASE STUDY – TSUNAMIS
Place – Indian Ocean
Size – 9.1 on the Richter Scale (earthquake off the west coast of Sumatra on 26th December 2004)
Cause – there’s a destructive plate margin along the west coast of Indonesia in the Indian Ocean.
↳ Around 230,000 people killed or missing.
↳ Towns or villages destroyed (1.7 million people lost their homes).
↳ Infrastructure damaged.
↳ 5 – 6 million people needed emergency food, water and medical supplies.
↳ Massive economic damage. (Millions of fishermen lost their livelihoods)
↳ Massive environmental damage caused. (Coral reefs destroyed by waves)
CASE STUDY – TSUNAMIS (Continued...)
· Millions of pounds was pledged by foreign governments, charities ect.
- Foreign countries sent ships, planes and teams of specialists to help rescue people, distribute food and water.
· Billions of pounds was pledged to help re-build infrastructure.
· A tsunami warning system was put in place.
- Disaster management plans were put in place in some countries.