natural hazards Flashcards
what are natural hazards
an event beyond human control that could threaten life and property
e.g. mount popocatepetyl
what is a natural disaster
a hazard that has already happened causing death and destruction
e.g. japanese tsunami
what is a natural event
an event that occurs such as a volcanic eruption or storm that do not pose a threat to humans
e.g. japanese island
what factors affect the impact of hazards
- size of event
- preparedness
- duration
- population (density)
- relative wealth
- links
what is the risk equation
hazard risk =
(vulnerability x hazard (type, frequency and magnitude) ÷ capacity to cope
what are the large pieces the earths crust is broken down into called
tectonic plates - move a few cm each year
what is the theory ab moving tectonic plates called
continental drift
who discovered continental drift
Alfred wegener
what are the 3 reasons Alfred Wegener thought the plates were moving
1) shells and salts up mountains
2) fossil mates across continents
3) uncanny “fit” between continents
what are the diff layers of the earth
- crust: relatively thin and rocky
- mantle: properties of a solid but can flow very slowly
- outer core: made from liquid nickel and iron
- inner core: made from solid nickel and iron
what if the diff. between continental and oceanic crust
- oceanic crust: younger, denser, thin (up to 10km), mainly has ocean on it
- continental crust: older, less dense, thick (up to 70km), mainly has landmass on it
what is the lithosphere
crust and upper part of the mantle
what is the area where the mantle and crust meet called
moho discontinuity
what are convection currents
- movement (caused by heat) in the mantle cause the plates to move v. slowly each year
how do convection currents cause plates to move
1) radioactive decay in the core heats the mantle
2) particles in the mantle close to the core become less dense as they are heated
3) particles rise nearer to the crust
4) as they move away from the core they cool and sink back down again
5) this creates a convection current
what is ridge push
magma pushes up the plate boundary causing the plates to be pushed apart
how does ridge push cause plates to move
1) the rising hot magma heats the surrounding rocks, causing them to expand and rise above surrounding land
2) where the plates move apart, the plates are pushed up. this means that gravity and the wight of the plate makes them move
what is slab pull
pull of gravity on a plate that is being subducted
how does slab pull cause plates to move
1) the oceanic plate is denser and heavier so is subjected beneath (forced under) the continental plate
2) as the plate sinks, it pulls the rest of he plate along with it
what are the 4 types of plate boundary + examples
- constructive = mid-Atlantic ridge
- destructive = japan
- collision = himalayas
- conservative/ transform = California
How do constructive plate margins work
- Convection currents in the mantle cause hot magma to rise, heating the rocks above them
- The tectonic plates move apart from each other bc of ridge push, the molten magma rises in between cools and forms new rock. This forms part of the new oceanic plate. The new plate sometimes fractures ad it is moved causing shallow usually small non-violent earthquakes.
- Most of the magma doesnt reach surface but pushes crust up to form ridges, magma that does rise spreads and solidifies forming shield volcanoes
How do destructive plate margins work
- Pressure of oceanic and continental moving towards each other - sudden jolts cause major earthquakes
- Denser oceanic plate is subducted and sinks under the continental plate - forms ocean trench
- As oceanic plate sinks deeper into mantle it causes part of plate to melt. Hot magma forms in a magma chamber under pressure. Eventually rises up and can erupt forming violent volcanoes. Magma is viscous so solidifies to form steep sided composite volcanoes.
How do collision plate margins work
- Two plates collide and bc they are made of same rock type neither gets subducted under, and as result compression forces plates to collide and form fold mountains. Earthquakes can occur here.
How do conservative plate margins work
- Pressure builds up at margin as plates are being pulled along as they are pushed by convection currents. Eventually pressure becomes too great, rock fractures in an earthquake and jolts into a new position
- Land is neither created or destroyed so no volcanoes.
Where else do volcanoes from
Hotspots where the crust is thin and magma is able to break the surface
Where are most earthquakes and volcanoes found
Ring of fire
- 70% of all earthquakes
- 90% of all volcanoes
Where did the 2016 New Zealand earthquake occur
North of South Island in Kaikoura, close to Christchurch
What were the effects of the New Zealand earthquake
- farmland destroyed = loss of money
- secondary earthquakes/tremors
- landslides
- homes destroyed
- £1bn in damages
- blocked roads
- 2 people died
Where did the 2015 Nepal earthquake occur
Close to capital Kathmandu
What were the effects of the Nepal earthquake
- 9000 dies
- 22k injured
- landslides and avalanches
- lack of clean water led to outbreaks of typhus
- 7.8 magnitude led to smaller earthquakes
- displacement of people
what were the primary effects of the Nepal earthquake
- damage to buildings
- crops destroyed
- landslides
- masonry crushing people
- explosion (gas station)
- comms cut off
what were the secondary effects of the Nepal earthquake
- food shortages
- delayed death - dehydration/disease (j: may be bigger in poorer countries)
- longer term power shortages
what caused the New Zealand earthquake
- magnitude 7.8 on nov 14 2016
- occurred near city of kaikoura, tectonically complex area w/ conservative and destructive plate boundaries
what caused the Nepal earthquake
- magnitude 7.8 28th April 2015
- shallow earthquake 15km below surface
- epicentre in gorkha district 80 km from capital
- indo-australian moving north at 45mm/year into eurasian
- multiple large aftershocks
