hazards Flashcards
4 layers of the earth
inner and outer core, mantle and crust
whats the lithosphere
crust and upper-most solid mantle
whats the asthenosphere
lies beneath the lithosphere, this layer is semi-molten which the plates float and more
how thick is the oceanic crust
6-10km
how thick is the continental crust
30-70km
what was pangea and who founded it
alfred wegener published a theory in 1912 that a single continent existed 300 million years ago
what were the north and south of pangea called
north- laurasia
south- gondwanaland
geological evidence for pangea theory
- the fit of south america and west africa
-evidence of late carboniferous glaciation, deposits from which are found in south america , antarctica and india - striations on rocks in brazil and west africa
- rock sequences in northern scotland closely agree with those found in eastern canada indicating they were laid down under the same conditions
biological evidence for pangea theory
- fossil brachiopods found in indian limestone are comparable with similar fossils in australia
-fossil remains of the reptile mesosaurus are found in both south america and southern africa, it is unlikely that the same reptile could have developed in both areas or that it could have migrated accross the pacific - the fossilise remains of a plant which existed when coal was being formed have been located only in india and antarctica
what was wegeners theory unable to explain
continental movement, so when the mid-atlantic ridge was discovered sea-floor spreading was occcuring, so subduction must be occuring elsewhere
whats ridge push
when plates move apart ( constructive boundary) the magma rises from the mantle. it creates new hot and dense rock, it pushes the old rock out the way creating a ridge in the crust ( also called gravitational sliding )
slab pull
gravity pulls the old rock into the mantle because the rock has become colder and denser, this occurs at subduction zones in destructive boundaries
where are hotspots and magma plumes located
located along the plate boundaries and alot of them are along the mid-atlantic ridge. however there are a few hot spots in the centre of the pacific plate which are not along the plate boundary
how are hotspots formed
radioactive decay within earth core generates very hot temps
-if decay is conc hotspot forms
-hotpsot heat lower mantle creting localised thermal currents where magma plumes rise
- these plumes sometimes cause volcanic activity in the middle of plate boundaries
-can form islands such as hawaiian islands
physical causes of earthquakes
on plate boundary margins
some occur away from plate boundaries and are associated with the reactivation of old fault lines eg uk
human causes of earthquakes
buildings of large reservoirs
deep mining
fracking
whats the focus
the point at which pressure is released within the earths crust
whats the epicentre
the point on the earth surface immediately above the focus. this is where the earthquake is felt and where the most intense ground shaking takes place
how deep is a shallow focus
0-70km
how deep is a intermediate focus
70-300km
deep focus
300-700km
4 different types of shock waves
primary/pressure waves
secondary/shear waves
surface/love
rayleigh
3 scales in which earthquakes are measured
richter scale
mercalli scale
moment magnitude scale( mms)
mercalli scale
this measures how much damage is caused by observations
measured on a scale between I AND XII
good for insurance purposes
primary impacts of earthquakes
ground shaking of which the severity depends upon the magnitude, depth, distance from epicentre and local geological conditions
ground rupturing wich is a visible breaking/displacement of earths surface, poses a threat to large structures such as dams brides and nuclear systems
secondary impacts of earthquakes
solid liquefaction
landslides/avalanches
tsunamis
fires
destroyed infrastructure
whats soil liquefaction
when vibrations/water pressure within a solid cause soil to loose contact with other particles. as a result soil behaves like a liquid and has an inability to support weight
causes lack of access meaning aid cant get to people quickly
whats a tsunami
giant sea waves generated by shallow-focus underwater earthquakes involving movements of the sea bed, or landslides into the sea
whats the first warning of a tsunami
the wave trough in front of the tsunami which results in a reduction in sea levels , known as drawdown
what percentage of tsunamis are generated in the pacific basin
90%
when was tohoku region of japan earthquake
2011
what was the magnitude of japan earthquake of 2011 and how far offshore was it
magnitude of 9 , 70km offshore
how many death in japan earthquake/tsunami of 2011
nearly 16000
how far inland did japan tsunami of 2011 reach
10km
what nuclear power plant was shut down in japan tsunami 2011
fukashima
primary effects of wildfires
smoke
loss of vegetation and crops
loss of life and injury to people and animals
destruction of property and possesions
secondary effects of wildfires
health problems from smoke inhalation
loss of animal habitats, homelessness, increased soil erosion, insurance premiums rise, access to recreational areas is restricted
peoples circumstances on their perception of hazards
wealth, religion, education, past experiences, personality
what is risk sharing
involves sharing the cost of reducing a hazard, the benefits of preventing it or the costs of not preventing it- eg people buy insurance to help them repair their property after a disaster. most people wont be affected by an event so they wont claim insurance- this means lots of people contribute so the cost is shared
fatalism
some people believe hazards cannot be avoided so they must just be accepted
what does the park model show
shows how responses progress during a disaster, which may help lanners predict what resources will be needed at each stage
pre-disaster, disruption, relief, rehabilitation, reconstruction. line graph. can help planners to prepare for future hazards.
hazard management cycle
4 stages- mitigation, preparedness, responce, recovery. its a cycle because hazards keep happening so efforts to prepare for them or mitigate their effects are ongoing
what is the core made u of
iron and nickel
what is the mantle made up of
mostly silicate rocks
convection currents
- mantle is hottest close to the core so lower parts of the asthenosphere heat up and become less dense and begin to rise
- as they move towards the top of the asthenosphere they cool down become more dense and slowly sink.
- this creates a drag on the base of the tectonic plates causing them to move
sea-floor spreading
as tectonic plates diverge( move apart) magma rises to fill the gap, then cools and forms new crust.
-over time new crust is dragged apart and more crust formed and the sea floor gets wider.
- creates structures called mid-ocean ridges of higher terrain on either side of the margin
constructive margins
occurs when 2 plates are moving apart (diverge). the mantle is under pressure from the plates above. when they move apart the pressure is released which causes the mantle to melt , producing magma ( forming volcano ). if plates dont move apart in uniform way the pressure is too much and the plate cracks forming an earthquake
rift valley
where plates diverge beneath land, as the plates keep moving apart the crust between the parallel faults drops down to form a rift valley. eg east African rift system, a series of valleys that stretch 4000km from Mozambique to the red sea. volcanoes such as mt kilimanjaro and mt kenya can be found around rift valleys
destructive margins (oceanic- continental)
move towards each other( converge ), more dense oceanic crust forced under the continental crust ( its subducted ). forms deep sea trenches, eg Peru-Chile trench in the pacific ocean. FOLD MOUNTAINS also formed here- made up of sediments that have accumulated on continental crust which are folder upwards. VOLCANOES also formed as oceanic crust melted by mantle and magma rises. when the pressure builds up as they subduct EARTHQUAKES are also created.
destructive margins ( oceanic-oceanic )
most of the same processes occur, the denser of the 2 is subducted forming deep sea trenches and triggering earthquakes and volcanic eruptions. islands arcs like mariana islands are formed by underwater volcanic eruptions
conservative plate margins
Earthquakes occur here as plates get locked together and pressure builds up. Fault lines also form as plates moves past each other, eg Sam Andrea’s fault
Primary hazards of volcanoes
Pyroclastic flow, lava flow , volcanic gasses , ash fallout and tephra
Pyroclastic flows
Cloud of super-heated gas, ash, volcanic rock
Lava flow
Speed and instance depends on viscosity
Volcanic gasses
CO2 sulphur dioxide
Ash fallout and tephra
Any rock / ash material
Secondary hazards
Lahars , acid rain
Lahars
Mudflow, volcanic materials mix with water
Short term responses to hazards
Evacuation , exclusion zones, emergency shelter and supplies
Long term
Strengthened buildings , tourism , monitoring systems , shelter, education
Moment magnitude scale
Based on total amount of energy released, logarithmic,, more accurate than richter
Conditions for storms
50 m deep water, 26.5c , coriolis effect , disturbance near surface such as low pressure
