why are some locations more at risk from tectonic hazards? Flashcards
the global distribution of plate boundaries can be explained by what?
plate boundaries and other tectonic processes
describe the earth’s structure
the inner core, outer core, mantle, crust
what are the two main tectonic plates? and what’s the difference between them.
oceanic: -underwater -thinner than continental crust -dense so it sinks -newer rocks continental -on land -thicker than oceanic crust -less dense (so it floats) older rocks
what are seismic waves?
shock waves released by tectonic movements
what are the four theories explaining plate tectonic movement?
Mantle Convection
Slab pull
Subduction
Seafloor spreading.
describe was is meant by mantle convection
Heat produced by the radioactive decay of material in the earth’s core heats the lower mantle-creating convection currents. These hot liquid magma currents are thought to move in circles through the asthenosphere causing the plates to move.
describe what is meant by Slab Pull
Newly formed oceanic crust at mid-ocean-ridges become denser and thicker when it cools. this causes it to sink into the mantle under its own weight- pulling the rest of the plate further down with it.
describe what is meant by subduction
As two oceanic plates (or one oceanic and one continental) move towards each other, one (usually the denser one) slides under the other into the mantle- where it melts in an area known as a subduction zone
describe what is meant by seafloor spreading
in the middle of many oceans are huge mid-ocean ridges (underwater mountain ranges). These are formed when hot magma is forced up from the asthenosphere and hardens (cooled). This forms a new oceanic crust which pushes the tectonic plates apart in a process called seafloor spreading.
what are the three different plate margins?
Destructive
Constructive
Conservative plate boundary
what happens at the conservative plate margin and what do they form?
Plates slide past each other
earthquakes
what happens at destructive plate margins and what do they form?
Plate slides under another plate
forms volcanos and earthquakes
(destructive collision zones)
Plates move towards each other
both plates are forced up and form fold mountains
what happens at constructive plate margins and what is formed?
plates move away from each other
forms volcanoes
what are some theories of plate motion?
- Alfred Wegener’s continental drift hypothesis in 1912 suggested that now-separated continents had once been joined as a continent names Pangea
- Arthur homes suggested in 1930 that the earth’s internal radioactive heat was the driving force of mantle convection that could enable the movement of tectonic plates
- the discovery in 1960 of the asthenosphere, a weak, deformable layer beneath the rigid lithosphere on which the lithosphere moves
- paleomagnetism involving ancient magnetism which causes the plates to move
what are transform zones?
where conservative plate boundaries consist of transform faults. These faults join up as they traverse the earth’s surface in a zig-zag pattern. Long transform faults like the San Andreas fault creates an area of frequent earthquake activity.
what are the causes of earthquakes?
Earthquakes are a result of a sudden release of stored energy. As tectonic plates attempt to move past each other along fault lines, they inevitably ‘stick’. This allows pressure to build up over time which is suddenly released (stick-slip behaviour). energy radiates out in all directions from the earthquake’s focus. in some cases, the earthquakes motion displaces the surface, creating a fault scarp.
what are the three types of waves earthquakes create?
P-waves: primary waves (fastest and cause the least damage)
S-waves: secondary waves (second fastest and shake ground violently causing damage)
L-waves: love waves (slowest, have a large amplitude and cause significant damage, Inc. fracturing the ground’s surface).
what are some secondary impacts of earthquakes?
landslides- most prone in areas of geologically young (and therefore unstable) earthquakes such as the Himalayas
liquefaction- areas where the ground consists of loose sediment such as silt, sand or gravel that is also waterlogged (often found near sea of rivers).
what are six secondary hazards of volcanos?
- LAVA FLOW: extensive areas of solidified lava which can extend several kilometres from the volcanic vents
- PYROCLASTIC FLOW: very large, dense clouds of hot ash and gas of temperatures of up to 600°C.
- ASHFALL: ash particles and larger tephra particles can blanket huge areas in ash, killing vegetation, collapsing buildings and poisoning water sources
- GAS ERUPTION: the eruption of carbon dioxide and sulphur dioxide, which can poison people and animals in extreme cases
- LAHAR: volcanic mudflows, which occur when rainfall mobilises volcanic ash. They can travel at high speed down river systems and cause major destruction.
- JÖKULHLAUP: devastating floods caused when volcanoes erupt beneath glaciers, and ice caps, creating huge volumes of meltwater. They are common in Iceland.
which of the volcanic secondary hazards occur in a composite volcano/subduction zone?
- lava flow
- pyroclastic flow
- ashfall
- gas eruption
- lahars
which of the volcanic secondary hazards occur in a shield volcano?
- lava flow
- gas eruption
which of the volcanic secondary hazards occurs on a constructive plate margin?
- ashfall
- Jökulhlaup
what are ways in which a tsunami is formed?
- landslides
- eruptions of volcanic islands
- (most commonly) sub-marine earthquakes in subduction zones.
describe how a tsunami is formed as a consequence of a sub-marine earthquake
Tsunamis are generated when a sub-marine earthquake displaces the sea bed vertically (either up or down) as a result of movement along the subduction zone or along a fault line.
The violent motion displaces a large volume of water in the ocean water column, which then moves outwards in all directions from the point of displacement.
the water moves as a vast ‘bulge’ in open water, rather than as a distinct wave.
what are some characteristics of a tsunami?
- wave height of typically less than 1m
- wavelengths are usually more than 100km.
- speeds are 500-950km/h.
what’s the difference between tsunamis in the open ocean and close to shore?
- out at sea: barely noticeable
- close to shore: wavelength drops but wave height increases making them noticeable.
