tectonic hazards Flashcards
buildings designed to withstand or minimise destruction during an earthquake
aseismic buildings
- the upper mantle layer of the earth. itis semi-molten and approximately 2000km wide
- largely composed of silicate rocks, rich in iron and magnesium
- temperature gradient (towards the core) generates convection currents
asthenosphere
fine particles and dust ejected during an eruption, which can remain airborne as clouds or accumulate on the ground
ash
- crust that forms the continents of the lithosphere, on average 35km thick
- high density of rock, mainly granite, thick, old
continental crust
the movement of tectonic plates, due to varying weights of crust. it was originally thought that convection currents caused the movement of the plates, but now Slab Pull is though of as the primary driving force
continental drift
the circulation of magma within the mantle (asthenosphere). magma is heated by radioactive processes in the core and cools at the surface, and so circulates between the two places.
convection currents
this model shows that a hazard becomes a disaster if it affects a vulnerable population
degg’s model
the point on the surface, directly above the earthquake’s origin
epicentre
the place in the crust where the pressure/seismic energy is released
focus
the sequence of governance of a natural hazard: monitoring and prediction, mitigation, preparedness
hazard mitigation cycle
- volcanoes found away from the plate boundary, due to a magma plume closer to the surface.
- localised area of the lithosphere which has an unusually high temperature due to the upwelling of hot molten material from the core
hotspot
a sudden glacial flood caused by a glacier on top of or near a volcano melting due to the heat from the eruption
jokulhaup
a flow of mud and debris
lahar
the upper crust of the earth (average thickness = 100km)
thinnest, least dense, lightest
lithosphere
- a surface earthquake wave with horizontal displacement
- only travel through crust
love waves
parting oceanic plates at a constructive plate boundary creates a ridge, with new land at the base of the oceanic valley
mid-ocean ridge
a measure of an earthquake’s energy released, considered the most accurate measure
moment magnitude scale
- crust, usually thinner than continental crust, forms the sea floor. it is on average 7km thick.
- low density of rock, mainly basalt, newly created
oceanic crust
- the study of rocks that show the magnetic fields of the earth.
- the alternating polarisation of new land created. as magma cools, the magnetic elements within will align with the earth’s magnetic poles, which can alternate over thousands of years
- each time these switch the new rocks being formed at plate boundaries allign in the opposite direction to the older rock
- evidence of sea floor spreading
paleomagnetism
a model describing the decline and recovery of a country over time, following a natural disaste
park’s model
elements within the lithosphere have different melting points, and so rock is partially melted, partially solid
partial melting
an earthquake wave causing compressions within the boddy of rock
primary rocks
a mixture of gases and rock fragments, at high temperatures travelling at rapid speeds
pyroclastic flow
a surface earthquake wave causing both horizontal and vertical displacement due to compressions caused in the ‘rolling’ earth’s crust
rayleigh waves
a logarithmic measure of earthquake’s intensity
richter scale
- an earthquake wave causing vertical displacement within the body of rock
- longer wavelength than and arrives seconds after primary waves
secondary waves
the energy released during an earthquake, in the form of primary, secondary, love and rayleigh waves
seismic waves
- the force contributing to the movement of the tectonic plates.
- slab pull is due to the weight of the plate
- as it subducts, it pulls the rest of the plate (slab) with it, causing further subduction
- primary mechanism for plate movement but used to be thought that it was convection currents
slab pull
oceanic plate is forced below continental plate, due to the oceanic plate being more dense than the continental plate
subduction
initial vertical water displacement (often from a submarine earthquake) creates waves, with large destructive powers
tsunami
a measure of the magnitude of a volcano’s eruptions
volcanic explosivity index (VEI)
a series of volcanoes (often in the shape of an arc) that are formed consecutively, as a tectonic plate moves across a magma plume.
volcanic island arc
a region of the subducting plate, most affected by pressure and friction, where most destructive margin earthquakes originate
wadati-benioff zone
what is a hazard
2 parts
- potential threat to human life and property
- can be either hydro-meteorological (caused by climatic processes) or geophysical (caused by land processes)
geophysical hazards
2 parts
- occur near plate boundaries
- these plates move at different speeds and directions which can cause collisions, earthquakes and volcanic activity
intra-plate earthquakes
3 parts
- earthquakes that occur near the middle of plates
- causes not fully undertstood but assumed that plates have pre-existing weaknesses which become reactivated, seismic waves.
- may occur if solid crust which has weakened over time, cracks under pressure
tectonic trends since 1960
4 points
- total number of recired hazards has increased
- number of fatalities has decreased but there are some spikes during mega disasters
- total number of people being affected by tectonic hazards is increasing due to population growth
- economic costs associated with hazards and disasters has increased significantly - partly due to increased in development as infrastructure is more developed so costs more to repair and also the number of insurance policies heightens the cost
why is reporting disaster impacts difficult and controversial
4 points
- depends on whether you look at direct deaths so those killed in the disaster straight away or indirectly by looking at people who died of a disease spread after the disaster - some impacts take time to become apparent
- location is important as rural and isolated areas are hard to reach and so it may be hard to collect data from them. similarly, data may be difficult to collect in areas with high pop densities
- different methods used by different organisations to different sources may quote different figures
- number of deaths quoted by the government could be subject to bias - maybe to show they are doing a good job in terms of aid, protection etc.
- dense, semi-molten rocks containing iron and nickel alloys
- at a depth of 2890km-5150k bello earths surface
outer core
- similar composition to the outer core.
- it’s over 5150km below the earth’s crust.
- solid due to extreme pressures itt experiences
- high temperatures
inner core
constructive plate boundaries
3 parts
- away from each other
- continental / continental forms volcanoes, earthquakes and rift valleys
- oceanic / oceanic causes volcanoes earthquakes and ocean ridges
conservative plate boundaries
2 parts
- parallel to each other in the same direction at different speeds or in opposite directions
- no plates destroyed so no landforms created
- lots of pressure built up when they move
- can displace lots of water on oceanic crust
- fault lines can occur on continental crust where ground is cracked by movement
- cause earthquakes
destructive plate boundaries
4 parts
- move towards each other
- continental / continental causes fold mountains and earthquakes
- oceanic / oceanic causes ocean trenches, island arcs, volcanoes and earthquakes
- continental / oceanic causes volcanoes, fold mountains and earthquakes
destructive continental and oceanic plate boundary
7 parts
- dense oceanic plate subducts below continental
- platee subducting leaves deep ocean trench
- oceanic crust is melted as it subducts into the asthenosphere
- extra magma created causes pressure to build up
- pressurised magma forces through weak areas in the continental plate
- explosive, high pressure volcanoes erupt through the continental plate, known as composite volcanoes
- fold mountains occur when sediment is pushed upwards during subduction
destructive oceanic and oceanic plate boundary
3 parts
- heavier plate subducts, leaving an ocean trench. fold mountains will also occur
- built up pressure caused underwater volcanoes bursting through oceanic plate
- lava cools and creates new land called island arcs
destructive continental and continental plate boundary
4 parts
- both plates are not as dense as oceanic so lots of pressure builds
- ancient oceanic crust is subducted slightly, but there is no subduction of continental crust
- pile up of continental crust on top of lithosphere due to pressure between plates
- fold mountains formed from piles of continental crust
constructive oceanic and oceanic plate boundary
3 parts
- magma rises in between the gap left by the two plates separating, forming new land when it cools
- less explosive underwater volcanoes formed as magma rises
- new land forming on the ocean floor by lava filling the gaps is known as sea floor spreading (as the floor spreads and gets wider) - evidence from paleomagnetism
constructive continental and continental plate boundary
4 parts
- any land in the middle of the separaetion is forced apart, causing a rift valley
- volcanoes form where the magma rises
- eventually the gap will most likely fill with water and separate completely from the main island
- the lifted areas of rocks are known as horsts whereas the valley itself is known as graben
ridge push
2 parts
- slope created when plates move apart has gravity acting upon it as it is at a higher elevation.
- gravity pushes the plates further away, widening the gap (as this movement is influenced by gravity, it is known as gravitational sliding)
density of plate
determines whether a plate subducts or is forced upwards which determines the landscape and hazards the margin is vulnerable to
Wegner’s contintental drift theory
3 parts
- the shapes of south america and africa seem to fit together so were once part of a supercontinent
- as plates moved the continent separated
- further verified by similar fossils found where these plates could have fit but are now separated by oceans
earthquakes
4 parts
- most powerful at destructive and conservative
- constructive: plates move at different speeds, builds pressure until plates crack causing fault lines. this results in the release of energy in the form of seismic waves which causes earthquakes
- destructive: one plate forced under other, gets stuck due to friction which produced energy, plates suddenly jerk past each other, energy quickly released as large seismic waves, forming powerful earthquake
- conservative: plates lock, when pressure is built it produces sudden seismic waves
earthquake waves that causes immediate shock
primary waves
tsunamis
4 parts
- produced by sub-marine earthquakes at subduction zones, causing water displacement and deep trough waves
- always secondary to earthquakes, adding to death tolls
- present additional damage to vulnerable communities such as accelerating coastal erosion, which is a case in malibu/santa monica in california
- movement of plates under the ocean causes an uplift of ocean water, disrupting sea bed
volcanic hazards
7 parts
- world’s active volcanoes found at destructive and constructive plate boundaries and hotspots
- eject magma, gases, ash and dust
- constructive: less dense than the plate so rises above it, forming a volcano such as those within the rift valleys
- destructive: subduction causes the melting of the oceanic plate, allowing for magma to rise on the crust to form a volcano - produces explosive volcanoes
- shape of volcano determines its destructive ability - super volcano is most destructive but seldom occurs, composite more dangerous than shield
- primary hazards involve lava flows and phreatic eruptions, pyroclastic flows
- secondary hazards involve water in the form of lahars and jokulhlaups
