Hazards - Tectonic Plates Flashcards
Subduction Zone (one form of collision boundary)
1) What plates are involved and what is the cause of their movement?
2) Which plate gets subducted and why?
3) What increases the pressure of the subducted plate?
4) What causes the magma to rise and cause a volcanic eruption?
1) The convection current in the mantle moves the oceanic plate & continental plate towards each other.
2) The denser oceanic plate is subducted under the less dense continental plate, forming a ocean trench.
3) The crust on the oceanic plate starts to melt and increases the pressure that builds up in the mantle.
4) High pressure causes magma ro rise through the cracks in rocks to the surface as it’s hotter and less dense than surrounding rocks.
5) It then leads to a violent eruption, forming a composite volcano, which are volcanic mountain range.
Subduction zone - 2
1) Which force is transferred between the plates?
2) How to the plates get stuck on each other?
3) Which kind of build up causes an earthquake?
1) As plates move past each other, it causes friction and forms an earthquake.
2) As the continental plate continues to move towards the oceanic plate, its huge slabs of rock grind against oceanic plate and get stuck on each other and also gets dragged down.
2) During this, it builds up lots of energy and when they get unstuck, the continental plate violently jumps back up causing an intense shaking of the ground, causing an earthquake.
Composite volcano aka Stratovolcanoes
1) Where are composite volcanoes located?
2) What is at the bottom of the volcano and what happens there?
3) How does the eruption occurs?
Pressure, steam
1) These are mainly found on the destructive plate margins and have a conical shape.
2) At the bottom, there is a magma chamber in which the magma enters from the earth’s crust, and it keeps collecting until the pressure is built up high, causing gases to expand and water becomes steam.
3) With time, the pressure builds up so high and causes the magma to rise through the cracks and an explosion or a volcanic reuption occurs.
Composite volcano - 2
1) How does the magma from the volcanoes exit?
2) What do craters do during an eruption?
3) What are fumaroles?
Atmosphere, carbon dioxide,
- Most of the magma travels up the main vent and exits the crater; some of the magma creates its own vent and cone, called the Secondary vent.
- Craters can throw materials like thick ash, lava, and rocks (aka volcanic bombs) into the atmosphere.
- Fumaroles are openings on the surface that acts like a natural vent from deep within the earth, that allows volcanoes to release steam and gas (sulfur dioxide and carbon dioxide).
Composite volcano - 3
1) Describe the lava at composite volcanoes?
2) Describe the structure of composite volcanoes?
andesitic
- Due to its location, the lava is thick and viscous due to high silicon and gas content, meaning the eruptions are more violent but occur less frequently.
- After every eruption, the lava exits; lava cools and solidifies (slow flow due to andesitic magam) with the thick ash, forming steep sides of alternate layers.
Andesitic magma means it has high silica and gas content
Shield volcanoes
1) Where are shield volcanoes located?
2) Describe the features and explain why it’s like that?
3) Do they occur frequently or not, and why?
silica, basaltic
1) These are found on the constructive plate margins and on hotspots.
2) Due to its location, it has thin and runny lava with low viscosity and therefore it can travel easily longer distance before it solidifies.
3) As a result of its slow flow of the lava, it forms gentle slopes of the sides with a wide base.
4) The volcano has a basaltic magma, meaning it has low silica and gas content and therefore the eruptions are not that violent.
5) Due the thin and runny lava, the shield volcano eruptions are more frequent because the lava doesn’t get any blockage within the vent.
Conservative plate margin
1) Describe the movements of the plates
2) How do the plates get stuck?
3) What results into an earthquake?
1) The plates either move in same or opposite direction at different speeds.
2) As they slide past each other, the edges of the plates get stuck on each other as they grind past.
3) It then builds up lots of energy to release themselves and they jolt back in movement, resulting in an earthquake.
the plates are not being constructed or destroyed, they’re ‘conserved’.
Destructive plate margin (one form of collision boundary)
1) Which plates are involved in this collision and give a reason for their movement?
2) What happens when the plates collide? name the lines
3) What causes an earthquake?
4) What causes a volcano?
1) Occurs between two continental plate margins moving towards each other (due to the convection current in the mantle) with nearly the same density.
2) When they collide, the crust of both plates start to move upwards, making ‘synclines’ and ‘anticlines’, forming fold mountains.
3) As plates grind and crack, at times they get stuck on each other and when the plates gain lots of energy to get unstuck, they jolt back out in movement, causing an earthquake.
No volcanic eruption due to no magma
Constructive plate margin
1) Describe the movement of the plate and give a reason
2) Why do the plates start to move away?
3) What causes volcanic eruption?
4) Can earthquakes be caused?
1) The convection current in the mantle moves the constructive plates away from each other; the sea-floor spreading as they are mostly under sea.
2) The magma rises up from the mantle; it cools off and spreads out at the surface.
3) Some of the magma solidifies and creates new crust over time, and begins to slowly move apart as two separate plates.
4) The crust gets split as magma and gases rise through the cracks, that get released out to the surface, forming a volcanic eruption.
5) Only weak earthquakes occur, mainly because the plates are moving away and not grinding.
