Destructive plate boundary
- Causes volcanoes, earthquakes and fold mountains.
- An Oceanic Plate and a continental plate move towards eachother. The denser oceanic plate gets forced under the lighter continental plate creating a volcano/deep oceanic trench(a very deep section of the ocean floor where the oceanic plate goes down)
- As the Oceanic Plate goes deeper into the mantle it melts in the subduction zone. The newly molten rock is lighter so rises towards the surface and causes volcanos on the earth's surface.
- The continental plate is crumbles by the collision of the two plates and is folden and forced upwards to form fold mountains.
- e.g. along the east coast of Japan.
Constructive plate boundary
- Causes Volcanoes and some earthquakes
- Two plates move away from eachother
- Magma rises to fill the gap between the two plates and cools, creating new crust
- Shield volcanoes can also form here, along the edges of the plate boundary due to rising magma
- e.g. at the Mid-Atlantic ridge
Conservative plate boundary
- Causes severe earthquakes
- Two plates moving sideways past eachother
- Two plates moving in the same direction but at different speeds
- e.g. San Andreas Fault, the North American plate and the Pacific plate are moving in the same direction but at different speeds.
There are two ways to form fold mountains:
- When one oceanic plate and one continental plate collide this causes fold mountains to appear as the sedimentary rock that has built up between them are folded and forced upwards to form fold mountains. Found at destructive plate margins, e.g. The Alps
- When two continental plates meet they smash together and the sedimentary rock folds upwards to form fold mountains. e.g. The Himalayas
Fold Mountains-Case Study
- The Alps is a Fold Mountain range
- Location: Central Europe-it stretches across Austria, France, Germany, Italy, Liechtenstein, Slovenia and Switzerland
- Formation: The Alps were formed about 30 million years ago by the collision between the African and the European plates
- Tallest peak: Mont Blanc
- Population: Around 12 million people
3 uses of the Alps:
- Farming: The steep upland areas are used to farm goats, which provide milk cheese and meat. Some sunnier slopes have been terraced off to plant vineyards.
- Hydro-electric power: The narrow valleys are dammed to generate HEP e.g in the berne area in Switzerland. Switzerland gets 60% of its electricty from the HEP stations in the Alps.
- Tourism: 100 million tourists visit the Alps each year making tourism a huge part of its economy. 70% of tourists visit the Alps in the winter for skiing, snowboarding and ice climbing. In summer tourists can go walking, mountain biking, paragliding and climbing.
- The Alps can also be used for Mining and Forestry.
How people have adapted to the conditions of the A
- Steep Relief: Goats are farmed there because they're well adapted to live on steep mountains. Trees and man-made defences are used to protect against avalanches and rock slides.
- Poor soils: Animals are grazed in most high areas as the soil isn't great for growing crops.
- Limited communications: Roads have been built over passes (lower points between mountains). It takes a long time to drive over passes as they can be blocked by snow so tunnels have been cut through mountains to provide fast transport links.
Formation of Volcanoes
Volcanoes are found at Destructive and Constructive plate boundaries.
They are caused by movement of tectonic plate.
- Active- erupt frequently
- Dormant- temporary inactive
- Extinct- never likely to erupt again
- Destructive: At destructive plate margins, the oceanic plate gets forced under the continental plate because it is more dense (this also creates ocean trenches). The oceanic plate is melted and destroyed. A pool of magma forms, as this keeps happening there is too much magma in the magma chamber so the volcano erupts to get rid of it.
- Constructive: At constructive plate margins, magma rises to fill the gap between the two plates, this forms a volcano.
Types of Volcano
1. Composite Volcanoes (e.g. Mount Fuji, Japan)- Made up of ash and lava that has erupted, cooled and hardened into layers. The lava is usually thick and flows slowly, hardens quickly to form a steep-sided volcano.
2. Shield Volcanoes (e.g. Mauna Loa on the Hawaiian islands)- Made up of only lava. The lava is runny. It flows quickly and spreads over a wide area forming a low, flat volcano.
3. Dome Volcanoes (e.g. Mount Pelee in the Caribbean)- Made up of only lava. The lava is thick and flows slowly, hardening to form a steep-sided volcano.
Volcanic Eruption Impacts- Case Study
The Soufriere Hills Volcano in Montserrat (small island in the Caribbean )Erupted 25th June 1997
- The capital city Plymouth was buried under 12m of mud and ash.
- Over 20 villages and two thirds of homes were destroyed by pyroclastic flows.
- Schools, hospitals, the airport and the port were destroyed.
- Vegetation and farmland destoryed
- 19 people died and 7 were injured
- Fires destroyed many buildings
- Tourists stayed away and businesses were destroyed desrupting the economy.
- Population decline - 8000 of the islands 12000 have left since the eruptions began
- Volcanic ash has improved soil fertility.
- Tourism is now increasing as people come to see the volcano.
Volcanic Eruption Responses- Case Study
- People were evacuated from the south to safe area in the north.
- Shelters were built to house evacuees
- Temporary infrastructure was was built e.g roads and electricity suppliers.
- The UK provided £17 million of emergency aid
- Local emergency services provided support units to search and rescue survivors.
Secondary/ Long-term responses:
- A risk map was created and an exclusion zone is in place, the south of the island is off limits while the volcano is still active.
- The UK has provided £41 million to develop the north of the island- new docks and an airport have been built in the north.
- The Montserrat Volcano Observatory has been set up to try and predict future volcanoes.
A supervolcano is a volcano that can erupt on a much bigger scale to a normal volcano.
Characteristics of a supervolcano:
- Flat (unlike normal volcanoes which are flat)
- Cover a large area (much bigger than normal volcanoes)
- Have a caldera (unlike a normal volcano which has a crater at the top)
Yellowstone is an example of a supervolcano. In the last 3 million years there has been 3 eruptions. The last eruption was 630, 000 years ago. The large volume of material erupted from the last yellowstone eruption caused the ground to collapse, creating a caldera (volcanic cauldron)
When a supervolcano erupts there will be global consequences:
- Thousands of cubic kilometres of rock, ash and lava will be thrown out (much more than normal volcanoes).
- A thick cloud of super-heated gas and ash will flow at high speed from the volcano, killing, burning and burying everything it touches.
- Ash will shoot kilometres into the air and block out almost all daylight over whole continents. This can trigger mini ice ages as less heat engergy from the sun will reach the earth. Crops will not grow, economies will collapse and it is believed that society would not survive.
- The ash will settle over hundreds of square kilometers (normal volcanoes usually cover a couple square kilometres).
- Earthquakes are caused by the tension that builds at plate margins:
- Destructive- tension builds up when one plate gets stuck as it is moving down past the other into the mantle.
- Constructive- tension builds up along cracks within the plates as the move away from eachother.
- Conservative margins- tension builds up when plates going past eachother get stuck.
Once the plates eventually jerk past each other, sending out shock waves (vibrations) these vibrations are the earthquake. The shock waves spread out from the focus. The nearer to the focus, the more powerful and stronger the waves are and they cause more damage.
Epicentre- point on the earth's surface straight above the focus
Focus-the point in the earth where the earthquake starts.
The Richter Scale
- Measures the amount of energy released (magnitude)
- Magnitude is measured using a seismometer - a machine with an arm that moves with the vibrations of the earth
- There is no upper limit to the Richter scale and its logarithmic
- Major earthquakes are above 5
The Mercalli Scale
- Measures the effects of an earthquake
- Observations are made of the earthquake and are measured on the scale 1-12
Tsunamis- case study
- Destructive Plate Margine
- Earthquake off the west coast of the island Sumatra (measured 9.1 on the Richter Scale)
- Triggered a tsunami with waves up to 30 m high
- 26th December 2004
- Indonesia, Thailand, India and Sri Lanka were all affected
- 230 000 people killed or still missing
- Over 1.7 million people lost their homes
- The infrastructure of many countries were severly damaged
- 5-6 million people needed emergency food, water and medical supplies
- Economic damage- tourism industry suffered, business's destroyed
- Environmental damage- salt from the seawater has meants plants can't grow in many areas
- Within days hundreds of millions of pounds had been pledged by foreign governments, charities, individuals and businesses to give survivors food, water, shelter and medical attention.
- Foreign countries sent ships, planes, soilders and teams of specialists to help rescue people, distribute food and water and begin clearing up.
- Billions of pounds have been pledged to help rebuild infrastructure of the countries affected.
- Programms have been set up to re-build houses and help people get back to work.
- A tsunami warning system has been put in place in the Indian Ocean.
- Disaster management plans have been put in placein some countries. Volunteers have trained locals on what to do when a tsunami happens again.