Unit 1-Fragile World Flashcards
Explain how evidence supports Plate Tectonic Theory
-Some continents fit together like a jigsaw puzzle. So therefore they must have been together at some stage, and they were and it was a mega continent named Pangea.
-Also, convection currents that work in the mantle have such powerful movements that it moves the earth’s plates.
-Third of all, similar fossils are found on different continents. This shows that these continents were once in close proximity or even joined as these species that we find as fossils could not have travelled over the ocean, for example, the Lystosaurus fossil can be found on three different continents (India, Africa and Antarctica).
-More evidence to support this theory is similar patterns of rock layers on different continents showing rocks were once close or joined, for example, coal has been found in Australia, Antarctica, Africa and South America and if we put these continents together as a jigsaw then we can see the coal ares are all in close proximity.
-Finally, a discovery of a ridge of mountains running along the middle of the Atlantic Ocean known as the Mid Atlantic Ridge was made - these were formed by underwater volcanoes and lava cooling. As lava cools the magnetic iron points to the north pole. It was known at the time that the earth’s polarity switches approximately every 100mill years and when this reversed from north to south, the iron particles in the
erupting magma aligned themselves with the Earth’s new polarity at that time – this
creates evidence of seafloor spreading. Seafloor spreading means that the plate’s oceanic crust moves.
Explain why earthquakes and volcanoes are found along plate boundaries.
At diverging plate boundaries, earthquakes occur as the plates pull away from each other. The magma rises upward from the underlying mantle along the gap between the two plates. We almost never see these volcanoes, because most of them are located on the sea floor.
At converging plate boundaries oceanic and continental crusts push into each other causing the oceanic crust to subduct into the mantle where it melts and then rises as it is less dense than the magma in the mantle. This thick and high in Silica magma burns through the crust and builds up until the pressure is too high and it explodes releasing thick lava and cooled molten rock and a huge pyroclastic flow destroying the surrounding area.
Earthquakes are caused by friction and pressure, when two plates at a conservative plate boundary rub against each other it creates pressure and when it releases there is a tremor called an earthquake.
How do volcanoes occur at constructive (divergent) plate boundaries?
At diverging plate boundaries, earthquakes occur as the plates pull away from each other. The magma rises upward from the underlying mantle along the gap between the two plates. We almost never see these volcanoes, because most of them are located on the sea floor. This boundary type is found at the boundary between the South american and african plates and between the Eurasian and North American plates.
How do volcanoes occur at destructive (convergent) plate boundaries?
At converging plate boundaries oceanic and continental crusts push into each other causing the oceanic crust to subduct into the mantle where it melts and then rises as it is less dense than the magma in the mantle. This thick and high in Silica magma burns through the crust and builds up until the pressure is too high and it explodes releasing thick lava and cooled molten rock and a huge pyroclastic flow destroying the surrounding area. This type of boundary is found at the Eurasian and Pacific plate boundaries and the Nazca and South American plate boundaries.
Explain the effects of the Monserrat volcano
The population fell by over 75% (from 12,000 to 3,000) due to risk and many never returned, 19 people died, 7 were injured, over 20 villages were destroyed, people still suffer from silicosis as a result of the quartz released during the eruption, tourists stayed away, fires broke out in gov HQs, ash from the eruption was quarried and sold, the ash improved soil fertility.
Explain the cause of a tsunami
A tsunami is a series of large waves generated by an abrupt movement on the ocean floor that can result from an earthquake, an underwater landslide, a volcanic eruption or, very rarely, a large meteorite strike. However, powerful undersea earthquakes are responsible for most tsunamis.
Human factors of the Haiti earthquake that made it so devestating?
- Low level of development (GDP of 659 vs 2900
- Haiti had no building standards, builders used poor concrete, the cement was weak
- Haiti’s debt is $4.5bn
- 70% of the population are unemployed or underemployed
- Dense population around the epicentre
What was Wegener’s theory on plate tectonics and what was his evidence?
Wegener proposed his theory of continental drift. Wegener proposed that the continents plowed through crust of ocean basins, which would explain why the outlines of many coastlines (like South America and Africa) look like they fit together like a puzzle.
Names and locations of major plates and plate boundaries?
The 7 major plates of the earth: African Plate. Antarctic Plate. Eurasian Plate. Indo-Australian Plate. North American Plate. Pacific Plate. South American Plate.
What are convection currents and why are they important?
Convection currents move very slowly in the mantle layer in a circular motion. Whatever direction the circular movement is going in that’s the direction the plate above that part of the mantle will move.
How do volcanoes and earthquakes occur at conservative plate boundaries?
At a conservative plate margin , the plates move past each other or are side by side moving at different speeds. As the plates move, friction occurs and plates become stuck. Pressure builds up because the plates are still trying to move. When the pressure is released, it sends out huge amounts of energy, causing an earthquake. The earthquakes at a conservative plate boundary can be very destructive as they occur close to the Earth’s surface. There are no volcanoes at a conservative plate margin. An example of this type of plate boundary is the boundary between the NA plate and the pacific plate.
