1.1 distribution of tectonic hazards Flashcards
1
Q
Types of plate boundaries - convergent: oceanic meets oceanic
A
- denser oceanic plate subducts under the lighter oceanic plate
- creates an ocean trench and earthquakes in the Benioff Zone
- creates earthquakes and tsunamis
- volcanoes form as mantle melts and creates submarine volcanoes
- over millions of years volcanoes form islands in a curved line (island arcs)
2
Q
Types of plate boundaries - convergent: continental meets continental
A
- plates are the same density so they don’t subduct
- as they collide they crumpled and are forced up creating fold mountains
- sometimes compressed denser layers subduct creating shallow (so severe) earthquakes
- eg Himalayas
3
Q
Types of plate boundaries - convergent: oceanic meets continental
A
- oceanic plate is denser so subducts under (lighter) continental plate
- this creates ocean trenches/fold mountains
- earth quakes are created in the Benioff zone
- friction created melts mantle causing volcanic eruptions as magma pushes through faults in the crust
4
Q
Types of plate boundaries - divergent: in oceans
A
- two plates move apart creating new crust
- forms mid ocean ridges (eg Mid Atlantic Ridge)
- minor shallow focus earthquakes are created
- submarine volcanoes along the ridge can create islands (eg Iceland)
5
Q
Types of plate boundaries - divergent: in continents
A
- two plates move apart
- creates rift valleys
- crust is stretched and breaks into parallel cracks (faults)
- land between faults collapses creating steep side rift valleys (eg the Great Rift Valley, Ethiopia)
6
Q
Types of plate boundaries - conservative
A
- two plates slide past each other
- results in major fault between the crust called a transform fault
- plates get stuck and pressure builds until it’s suddenly released
- this creates powerful shallow focus earthquakes
- eg San Andreas Fault, California
7
Q
How do intraplate earthquakes occur
A
- in the interior of the plate
- along old fault lines which reactivate
eg Ramsgate Kent 2015 - collision of plates can fracture the crust well away from the boundary
- eg Tibetan plate
8
Q
how are earthquakes distributed
A
- majority close to or on plate boundary
- ring of fire
- usually most powerful on convergent or conservative boundaries
- intraplate earthquakes are often linked to hotspots
9
Q
how are volcanoes distributed
A
- most active occur at or near plate boundaries
- 75% on ring of fire
- generally convergent and divergent
- hotspots (Hawaii)
10
Q
how are tsunamis distributed
A
- 70% in pacific ocean
- mostly at convergent boundaries
11
Q
how do intraplate volcanoes occur
A
- result of upwelling of hot molten material (mantle plume)
- high heat and low pressure at the base of the lithosphere enables rock to melt
- magma rises through cracks in the crust and erupts
- as the plate moves over stationary hotspot, new chains of volcanoes / volcanic islands form
