1b.2 DM - Destructive Plates and Composite Volcanoes Flashcards
What landforms could be found at a destructive plate boundary?
Ocean trench
Subduction zones
Composite volcanoes
What’s the difference between continental and oceanic crust?
Continental is thicker.
Oceanic is thinner.
Oceanic is denser
Continental is lighter.
Continental is granitic.
Oceanic is basaltic.
What happens when plates converge?
Gravity causes the denser oceanic crusts to subduct.
This drags the rest of the tectonic plate down.
What hazards happen at destructive plate boundaries?
Volcanoes (composite)
Tsunamis
Earthquakes
Why do tsunamis happen at destructive plate boundaries?
Undersea earthquake activity as the continental and oceanic plate scrape past each other
Why do earthquakes happen at destructive plate boundaries?
The plates converge
The oceanic subducts
It scrapes past the continental plate, building up tension, which is then released
How do volcanoes occur on destructive plate boundaries?
Convection currents - the plates collide.
Denser oceanic crust is pushed downwards into the mantle, and melts.
Melted crust has greater gas content
Magma is viscous / andesitic
Composite / explosive volcanoes forms
What’s the shape of a composite volcano and why?
Steep, and tall.
Viscous lava doesn’t run very far before it cools, so you get steep sided volcanoes.
The crater is filled with a plug of cooled rock.
The volcano is made up of layers from lava and ash.
Why do earthquakes happen on conservative plate boundaries?
Plates slide past each other Friction occurs Build up of pressure -- the release of that pressure causes the earthquake. This point is called the focus.
What’s the difference between the focus and epicentre?
Focus is underground - where the earthquake begins.
The epicentre is above the ground - where the EQ waves reach the surface.
Why are some earthquakes more hazardous?
Higher magnitude (Richter scale)
The focus/epicentre is closer to densely populated area
Shallow focus
Can create secondary hazards - tsunamic landslides etc
What can cause a tsunami?
Earthquakes Landslides Underwater volcanic eruptions Large meteor strikes Upward movement of a tectonic plate / movement of plates
How do earthquakes cause a tsunami?
Plate movement causes the EQ
Energy is transferred to the water, causing it to move - the water column is displaced
This creates large waves
How do landslides causes a tsunami?
Water is displaced
This creates large waves
What is the focus and epicentre of an EQ
Focus - where the EQ starts
Epicentre - where the waves reach the surface
