Plate Tectonics Year 9 Test Flashcards
- Explain how evidence supports Plate Tectonic Theory.
The plate Tectonic Theory is that all the continents were once, one big continent called Pangea. This theory was created by the geologist Alfred Wegener in 1912. As millions of years have passed Pangea has separated into smaller continents. Pangea started separate due to natural disasters like earthquakes and volcanoes. As the years go on still the continents are moving further and further apart by 2cm annually. This is also caused by convection currents occur constantly under the mantle.
- Explain why earthquakes and volcanoes are found along plate boundaries.
Earthquakes and volcanoes are found at plate boundaries because when two plates rub it causes friction within the boundaries. Each plate has a certain direction that it moves against another plate. E.g. the African Plate is moving into the Arabian Plate. When this happens it creates friction and heat between the two plates. Meaning that when they rub an Earthquake could occur if enough friction has built up over time.
- Explain how earthquakes and volcanoes occur at Destructive plate boundaries.
Earthquakes and volcanoes occur because of the convection currents that occur beneath the Earth’s surface. These convection currents are slowly moving plates apart 4cm a year. A volcano then starts to form when the upper part of the mantle starts to melt. Magma then starts to rise through the gap and forms shield volcanoes and small, but frequent earthquakes. Eurasia and North America where once two joint plates but when they started separating it created volcanoes along their plate boundaries and earthquakes near the volcanoes. Earthquakes and volcanoes can also form at plate boundaries because of the convection currents.
- Explain how earthquakes and volcanoes occur at Constructive plate boundaries.
Earthquakes and volcanoes form at Conservative plate boundaries because two plates are sliding past each other. For example the Pacific Plate which moves North at 6cm/year and the North American plate which also moves North but at 1cm/year. When the plates start to slide past each other they create friction. The pressure then slowly build up and is suddenly released into an earthquake. When two plates like the Indian Plate and the Antarctic Plate slam into each other, this is caused by convection currents below the mantle. The plates are both made of the same material so they both are forced upwards. As the two plates collide and push together, the plates get jammed/locked due to friction. This causes earthquakes and volcanoes to occur.
5.Explain the effects of the Montserrat volcano (including facts)
The Montserrat volcano forced many people to move country for life due to the risk. The population declined from 12,000 to 3,000. Large areas including Plymouth, the capital of Montserrat were destroyed as they were covered under 12m of ash and mud this also caused a lot of vegetation to be damaged and ash and crops were destroyed. Over 20 villages and 2/3rds of the buildings were destroyed, this meant that many people had no home and therefore were left very poor. Fires broke out as hot lava set fire to government buildings and police Head Quarters. 19 people died and 7 were injured. Tourists stayed away for the following year as resorts were damaged - income was lost and jobs and the reputation were affected. The airport and port was destroyed which meant it was harder to get into the country. The country was in debt so therefore could not afford to rebuild any airports or ports. Schools and hospitals were destroyed. There are some positives from the Montserrat eruption. Volcanic ash was quarried and sold abroad - Montserrat now earns income from geothermal heat and quarrying in mines. Tourism has now increased as people are visiting the volcano and jobs have since been created.
- Explain why human and physical factors caused the Haiti earthquake to be so destructive.
Some Physical factors for the Earthquake being so destructive was because the magnitude of the shockwaves was a 7 and the focus was very shallow only 8-10km. The location of the epicentre was also in a very densely populated area just 15km from the capital city of Port-Au-Prince. The Human factors of the Earthquake being so destructive was because the country had a warm tropical climate, this meant that disease spreads rapidly. There was poor construction standards, when buildings were built there was no rules and there were no architects. Little amounts of fresh water, roads and electricity, this meant that it is harder for the country to recover. 50% of the population were in poverty meaning that they had no money to fund recovery. The country was in debt to other countries, this meant that not much money was spent on on recovery. The government took too many shortcuts causing more damage. There were a lot of steep slopes which meant that foundations couldn’t be built to a good standard.
- Explain the cause of a Tsunami?
If one tectonic plate is dragged beneath another, stress on the boundary causes the edges of the plates to flex and deform. The flexing of the plates displaces the entire column of water vertically. Quickly the water column splits into 2 with one wave traveling out to sea and the other towards the coast. The cause of a Tsunami is when one plate is sub ducting below the other. For example, the Indo-Australian was sub-ducting below the Eurasian Plate. If the focus is very shallow then the tsunami will have a huge amount of energy. Tsunamis are usually triggered by Earthquakes. Pressure builds up at the destructive subduction zone and eventually the stress was released when the continental plate flicks upwards. As the wave approaches shallow water, it slows down and the wave builds in height (Wave amplification). When the crust shifts this is the primary effect; a knock-on (secondary) effect of this is the displacement of water above the moving crust. This is the start of a Tsunami.
