hazards Flashcards
what is a chaparral?
tangled shurbs and thorny bushes
what is a crown fire?
a forest fire that spreads from treetop to treetop
what are fohn winds?
a warm dry southerly wind developing in the lee of any mountain range
what is glowing combustion?
when the fire begins to slow down
what is preheating?
fuel dries out due to nearby flames or hot weather
what does pyrolysis mean?
wood breaks down chemically, releasing gases, oils etc
what are pyrophytes?
plants adapted to tolerate fire
what are retardants?
chemicals sprayed on to fires in order to slow them down
what are wildfires?
are unctrolled fires that occur away from urban areas
what two key factors are needed to cause and spread a wildfire?
-ignition source, e.g sunlight, lightning, out of control campire
-fuel:dry vegetaion, leaf litter, trees with a high resin content
what are the stages of widlefires?
-stage 1:preheating
-stage 2 :flaming cobustion
-stage 3:glowing combustion
what happens in stage 1 of a wildfire?
-before the fire lights
-materials now ready for ignition
what happens in stage 2 of a wildfire?
-after ignition
-burning gases cause fast,hot fire
-wood cracks, releasing more gases, resins, oils which are then ignited
what happens in stage 3 of a wildfire?
-after ignition
-wood burns more slowly at a lower temperature
-fire consumes the wood (instead of gases released by pyrolysis)
how can vegetation type effect wildfires?
-small twigs and leaves burn easily
-grassland fires=cooler than forest fires
-grases, shrubs and debris means fater spreading fires and cooler (900 degree c)
-canopies of trees means crown fires
-pine needles burn easily
-large volume to surface peices dont burn as easily
-savanna chaparal the vegetation is most flammable
-loose bark means fire spreads uptree
what is the speed and direction of movement of a wildfire dependant on?
the type of vegetation, climatic characteristics and the local topography
what are fuel characteristics?
-moisture content
-content of resins, volatiles oils, waxes
-arrangements of fuel elements
-size and distribution of fuel elements
-energy content of fuel
-quanity of fuel
how do cliamates affect wildfires?
-most wildfires occur after prolonged dry periods
-heatwaves and droughts and cyclical climatic events create favourable conditions for wildfires
-strong dry winds blowing from continental interiors or deserts exacerbate the drying process
what physical factors contribute to intense wildfires?
-winds of differing speeds
-high relief
-time of day
what are the causes of wildfires?
-physical and exacerbating factors:lightning, lava flows near forest
-human factors and exacterbating factors:careless disposal of cigarettes, out of control campfires, bbqs,arson,playing with matches, agricultural burning
-exacerbating factors:climatic conditions, proximity to urban areas, type of vegetation (and abundance of it)
what happens to the solar energy stored by plants in a wildfire?
returned to the atmosphere during the fire
what do you need for the formation of a tropical storm?
-ocean to be 27 degrees
-60m depth
what happens in the formation of a tropical storm?
-clouds form as air cools and condenses
-warm moist air is drawn in at the base
-a central vortex is created as air rises and starts to spin
-at 15-20km above sea level winds spiral outwards
why do storms rotate?
because of the coriolis effect
what are the charateristics of the eye of the storm?
-calm in the centre
-most dangerous part of the storm
-sinking air and high winds
what are the hazards associated with tropical storms?
-stray winds
-storm surges
-river and coastal flooding
-landslides
strong winds:
-average wind speeds in excess of 120 km/h (75mph)
-gusts of over 250km have been recorded at the eye wall
-capable of tearing off roofs, breaking windows and damaging communication networks
storm surges:
-a surge of high water, typically up to about 3m in height, which sweeps inland from the sea, flooding low lying areas
-it is caused by a combination of the intense low atmospheric pressure of the tropical storm together with powerful, driving surfae winds
coastal and river flooding:
-the warm humid air can generate torrential rainfall, often in excess of 20mm in just a few hours. this can trigger flash flooding at the coast when the surface water can overwhelm the drainage system
landslides:
-the intense rainfall increases pore water pressure, which weakens cohersion and triggerin slope faliure. the additional weight of water exacerbates the problem
what does frequency mean?
how often it occurs
what does regularity?
same time difference between the event
what is the storm return period?
time between the storms of varying magnitude
what are the primary impacts of tropical storms?
-loss of life
-destruction of buildings
-strong winds
what are the secondary impacts of tropicall storms?
-economic loss
-displacement
-reduced tourism
what are the environmental impacts of tropical storms?
-induction of salt waters
-desstruction of coastal environment
-pollution
what are the social impacts of tropical storms?
-death
-injury
-disruption if lives
what are th eeconomic impacts of tropical storms?
-finacial costs of tropical storms
-cost to government
-cost to insurance companies
what are the political impacts of tropical storms?
-political issues of command and control
-local/regional/international disaster
-international aid from governments
predictability of tropical storms?
-tropical storms mostly occur in predictable locations and at specific times of the year
-this enables us to predict the season and locations in which they are likley to occur
asthenoshpere:
central molten (solid lower down)
mantle:
-silicate rocks
-rich in magnesium
-extends to depth of 2100km
-temp may reach 5000 degrees c
-high temps may generate to convection currents in the asthenosphere
crust:
-oceanic 6-10km thick
-continetal crust up to 70km thick
lithosphere:
-crust and ridged outer layer of the mantle
moko (mokolorovic):
-discontinuing= seperates the crust from the mantle
gutenburg discovery:
seperates the mantle from the core
core:
-iron and nickel
-outer core=semi molten
-inner core= solid
-temp at the centre=6200 degrees c (hotter than the surface of the sun)
how old is the continental crust?
over 1500 million years old
how old is the oceanic crust?
less than 200 million years
what is the density of continetal crust?
2.6
what is the density of oceanic crust?
3.0
composotion of conitnental crust?
mainly granite,silican aluminium, oxygen
composition of oceanic crust?
mainly basalt , silican, magnesium and oxygen
mantle convection:
- radioactive decay of some elements in the mantle and core, e.g uranium, generates a lot of heat
2.when lower parts of the asthenosphere heat up they become less dense and slowly rise
3.as they move towards the top of the asthenosphere they cool down and become more dense and slowly sink
4.these circular movements of semi-molten rock are called convection currents
-convection currents in the athenosphere create drag on the base of the tectonic plates(which are solid and ridgid) and this causes them to move
slab pull ridge push:
hess connected convection currents to ridge-push and slab-pull; he suggested they seem to work together.(gravitational sliding)
gravitational sliding:
-gravitational forces acting within the crust that also contribute to plate movement
-gravitational sliding away from a spreading ocean ridge takes place with plate movement, driven because of higher elevation of plates at ocean ridges. as fresh magma wells up at mid-ocean ridges to form new young, oceanic lithosphere a higher elevation is formed at spreading ridges.the new oceanic crust gradually cools and thickens with age and is pushed ‘downhill’ as new magma emerges from the active zone of divergence behind it
-slab pull is thought to be the more significant gravitational force acting on the plates. in the current understanding of plate motion the movement is driven by the weight of cold, older, dense plate material sinking into the mantle at deep ocean trenches pulling the rest of the plate slab with them as gravity causes them to slide downwards
sea floor spreading:
-takes place at mid ocean ridges and produces basalt, the rock that makes up the oceanic crust
-one of the 2 major process of forming new ingeous rock at mid ocean ridges by injection of magma that forms new sea floor
-produces major characteristics of the sea floor 1) the age of the seafloor is progressivley older away from mid ocean ridges,2)the elevation of the seafloor is progressivley lower away from mid ocean ridges, 3) the magnetic history of the history of the sea floor bears the striped-pattern of the earth magnetic reversals, and 4) older parts of the sea floor have the greatest potential to have accumilated sediments over time
-sea floor spreading determines plate motion around a mid ocean ridge
-also drives the direction in which continents move
what is an example of a constructive oceanic- oceanic boundary?
atlantic ridge
what processes happen at a constructiv oceanic-oceanic boundary?
-divergence
-crustal uplift
-fracturing
-ridge push
-gravitational sliding
-tensional forces
-sismicity
-transform faulting
what landforms do you find at a constructive oceanic-oceanic crust?
-fissures
-sheild volcanoes
-mid ocean ridge
-abyssial plain
-central rift
-hydrothermal vents
what type of laval is found at constructive oceanic-oceanic boundaries?
-basalt (1100 degrees c)
-fast flowing and runny
what are the nature of eruptions like at constructive oceanic-oceanic?
-sheild volcano
-fissure eruptions
give an example of a divergent continental-continental boundary
east african rift valley
what processes occur at a divergent continental-continental boundary?
-divergence
-rifting
-crustal uplift
-magma plumes
-fissuring
-gravitational sliding
-ridge push
-sea floor spreading (early)
what landorms occur at divergent continental-continental boundaries?
-central horst
-divergent plate boundaries
-rift valley
-horsts (raised)
-graben (valley)
what types of lava are found at divergent continental-continental boundaries?
basaltic but some andesite due to taking silican from the rock
what is the nature of eruptions like at divergent continental-continental boundaries?
-lava
-ash
-tephra
-poisonous gases
what processes are at destructive continental-continental?
-convergence
-subduction
-frictional heating
