Hazards - Plate Tectonics Flashcards
What is the lithosphere?
Broken up into plates, majority of the lithosphere is within the mantle. The top of the lithopshere is the crust.
What is the mantle?
Mainly solid rock high in silicon. The very top layer of the mantle is semi-molten magma, known as the asthenosphere.
What is the outer core?
Semi-molten, contains iron and nickel.
What is the inner core?
Solid ball of iron/nickel. Very hot due to pressure and radioactive decay. This heat is responsible for the Earth’s internal energy and it spreads throughout.
What is the asthenosphere?
Semi molten layer constantly moves due to convection currents. Movement is powered by heat from the core. Below the lithosphere.
What is the crust?
Top of the lithosphere, oceanic crust is dense and is destroyed by plate movement, continental crust is less dense and is not destroyed.
How are convection currents achieved in the mantle?
1) Heat from the inner core convects through the mantle into the asthenosphere.
2) Hot magma rises because it becomes less dense with heat (spreads out)
3) Magma is cooler at the top as it is further away from the heat source. Becomes more dense and sinks back down to the bottom.
4) Cooler magma is reheated and begins to rise again, creating a loop called a convection current.
What is slab pull?
Slab pull occurs on destructive plate margins, the dense crust is formed under and the sinking pulls the plate towards the boundary.
What is ridge push (gravitational sliding)?
Ridge push occurs on constructive plate margin, magma rises and forms new crust, moves downslope and puts pressure on the plates.
What is sea floor spreading?
Occurs at constructive plate boundaries.
1) As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense.
2) The less dense material rises, often forming a mountain or elevated area of the sea floor.
3) Eventually the crust cracks.
What movement occurs at a conservative plate boundary?
The plates move parallel to eachother. No plates are destroyed so no landforms are created. Lots of pressure is built up. On oceanic crust, this movement can displace a lot of water and on continental crust, fault lines can occur where the ground is cracked by the movement.
What movement occurs at a constructive plate boundary?
Plates move away from eachother.
What movement occurs at a constrcutive plate boundary between two oceanic plates?
1) Magma rises in between the gap left by the two plates separating, forming new land when it cools.
2) Less explosive underwater volcanoes formed as magma rises.
3) New land forming on the ocean floor by lava filling the gaps is known as seafloor spreading.
What movement occurs at a contructive plate boundary between two continental plates?
1) Any land in the middle of the separation is forced apart, causing a rift valley.
2) Volcanoes form where the magma rises.
3) Eventually the gap will most likely fill with water and separate completely from the main island.
What movement occurs at a destructive plate boundary?
Plates move towards eachother.
What movement occurs at a destructice plate boundary between a continental and oceanic plate?
1) Denser oceanic plate subducts below the continental, leaving a deep ocean trench.
2) Fold mountains occur when sediment is pushed upwards during subduction.
3) Explosive, high-pressure volcanoes erupt through the continental plate known as composite volcanoes.
What movement occurs at a destructice plate boundary between two oceanic plates?
1) Heavier plate subducts leaving an ocean trench. Fold mountains also occur.
2) Built-up pressure causes underwater volcanoes.
3) Lava cools and creates new land called island arcs.
What movement occurs at a destructice plate boundary between two continental plates?
1) Both plates are not as dense as oceanic so lots of pressure builds.
2) Ancient oceanic crust is subducted slightly, but there is no subduction of continental crust.
3) There is a pile-up of continental crust on top of the lithosphere due to pressure between plates.
4) Fold mountains formed from piles of continental crusts.
How do young fold mountains form?
Fold mountains are produced where two or more of Earth’s tectonic plates are pushed together. The plates push layers of accumulated sediment in the sea into folds between them. (Occur on destructive plate boundaries)
How do rift valleys form?
A long, deep valley found in the centre of a spreading ridge. It is formed between parallel faults where a block of the crust has sunk down.
How do ocean ridges form?
Mid-ocean ridges form along constructive plate boundaries, where new ocean floor is created as the Earth’s tectonic plates spread apart.
How do deep sea trenches form?
Trenches occur through subduction, which occurs when tectonic plates collide and push one plate beneath eachother. Trenches can be found all over the surface floor of the ocean at subduction zones.
How do island arcs form?
Island arcs are created when two oceanic plates collide, forcing one plate beneath another in a subduction process. This forces the subducted plate deep below the surface where it melts, and the molten rock rises to form volcanoes that can emerge as islands.
How do volcanoes form?
Volcanoes form when one tectonic pare moves under another.
What are magma plumes and how do they relate to plate movement?
Hot spots form around the core of the Earth where radioactive decay is concentrated, this extreme heat creates magma plumes. These are upwellings of super heated rock that rise from deep in the Earth’s mantle towards the surface. They can break through the middle of a tectonic plate to reach the surface causing volcanic activity and the earthquakes far away from plate margins.
What is paleomagnetism?
Studying rocks containing minerals formed in underwater volcanic eruptions aligning themselves in direction of Earth’s magnetic pole. Mapping locations of rocks showed migration and how Earth’s magnetic poles periodically reverse. Newer rocks were found at plate boundaries whereas older rocks were found further away suggesting land was splitting – sea floor spreading.
What gives evidence for sea floor spreading?
Paleomagnetism provides evidence that the sea floor has gradually moved apart at a mid-ocean ridge. Lava cools and solidifies with the minerals lining up with the magnetic field. The direction of the minerals on either side is a mirror image.
What gives evidence for continental drift?
1) The continents ‘fit together’
2) Fossil remains are constant across continents.
Describe the theory of continental drift
1) In 1912, Alfred Wegener published a controversial theory which suggested that the Earth’s continents had once been part of a single landmass called Pangaea.
2) He believed that the continents had gradually drifted apart over millions of years.
3) He was unable to suggest a cause of the movement and many scientists reacted with scepticism.
4) Today the theory is widely accepted and is recognised as the basis of the modern theory of plate tectonics.
