physical Flashcards
(15 cards)
1
Q
what is a divergent/constructive plate boundary
A
- plates going away from each other allowing magma to rise through the asthenosphere
- usually at mid-ocean ridges (long chains of mountains rising 3km above the sea bed)
- only volcanic activity
2
Q
what is a convergent/destructive plate boundary
A
- oceanic plates subducted under continental plates
- ocean trenches form so ocean gets deeper
- both volcanic and earthquakes occur
3
Q
what is a oceanic-oceanic plate boundary
A
- 2 oceanic plates collide
- slightly denser will subduct creating a trench
- descending plate melts and as magma rises to the top and forms island arcs
4
Q
what is a continental-continental/collision plate boundary
A
- little subduction
- mountain ranges form- Himalayas
- similar densities
5
Q
what is a conservative plate boundary
A
- 2 plates moving along side each other
- only earthquakes from the release of friction
- eg San Andreas fault
6
Q
3 ways as to why tectonic plates move
A
- ridge push- higher elevation new plate material being pushed outwards
- slab pull- plates being subducted pulling the rest of the plate with it
- solid convection- small amounts of liquid at the bottom of the mantle allow the plates to slide
7
Q
what is a hotspot
A
- volcanic activity away from a tectonic plate boundary
- in areas of the mantle where heat rises as a thermal plume from deep in the earth
- eg the Hawaiian islands
- as the plate moves the hotspot stays in the same place leading to the formation of multiple islands
8
Q
what is a Rift Valley
A
- magma rises through the crust creating cracks
- as the plates move apart rift valleys are formed
- a lowland region that forms where Earth’s tectonic plates move apart
- africa- 7000km length, east african rift valley
9
Q
what is a super volcano
A
- a volcano that erupts more than 1000km³
- exists as giant calderas such as Yellowstone caldera 75km across
- very rare, last one was 27,000 years ago
10
Q
proof of volcanic eruption at Yellowstone
A
- geyser- water under pressure which is heated and erupts often
- fumaroles- mud spots which are heated, hydrothermal
- hot springs- water which emerges from the ground and is heated, hydrothermal
11
Q
what are some hazards associated with volcanoes
A
- lava flows- streams of molten rock
- pyroclastic flows- dense, fast moving flow of solidified lava piece, volcanic ash and hot gases
- tephra- all the rock ejected into the air
- toxic gases- CO, CO2, SO₂
- lahars- a hot or cold mixture of water and rock fragments that flows down the slopes of a volcano
- floods- eruption below ice causes rapid melting
- tsunami- violent eruptions can cause the displacement of water
12
Q
why do people live near volcanoes
A
- economic- jobs, cheap energy, no income to move, cheaper housing
- social- low perception of risk, low frequency of hazard, family connections, technology
- environmental- fertile soil, good views
13
Q
ways to manage risk
A
- government- provide money, expertise, provide information
- scientists provide research and monitoring capacity
- intergovernmental- WOVO
- charities, NGOs
- people themselves- emergency kits, first aid training, up to date with developments, knowing what to do
14
Q
what is seismicity
A
- the frequency of earthquakes
- 750,000/year
15
Q
what are types of hazards posed by earthquakes
A
- ground shaking
- liquefaction- loosely packed water-logged sediments this causes the ground to lose strength and things can fall through
- landslides and avalanches
- tsunamis
