global hazards

what causes wind?

• the sun heats the earth because light passes through the atmosphere and is absorbed by the earth’s surface

• when the earth is heated by the sun, it radiates heat and heats the air above it

• the air that is heated expands and becomes less dense

• air that is less dense will rise above air that is denser, this creates low pressure at the surface

• the rising air cools, this causes condensation, clouds and percipitation

• rising air eventually reaches the upper atmosphere and spreads out

• this creates high level winds

• the high level winds that have spread out in the upper atmosphere sink back down to create high pressure

• sinking air gets warmer and so there is no condensation, clouds or rain

• high pressure air at the surface moves towards low pressure air at the surface creating surface winds

outline the global circulation system

• the equator receives more energy from the sun and is therefore hot

• hot air rises from the equator, this creates low pressure

• as air rises it cools, this causes condensation- this creates clouds and percipitation

• high in the atmosphere above the equator the air moves north and south

• where it sinks it creates high pressure at 30° north and south

• winds blow from high pressure to low pressure areas

• winds don’t blow in straight lines because of the spin of the earth (coriolis effect)

• the trade winds are at the surface and blow from 30° north and south towards zero degrees at the equator

what are the effects of high and low pressure belts in creating climatic zones?

• the atmospheric circulation results in high pressure at the poles, so they are very dry (polar cell)

• a low-pressure belt runs around the globe at about 60°, making locations such as the uk wet (ferrel cell)

• there is a band of high pressure around the tropics, so they are dry, with most of the world’s hot deserts found in these regions (hadley cell)

how does the global circulation of the atmosphere cause extremes in weather conditions in different parts of the world?

• sub-tropical (desert) climate:

  -30° north and south of the equator there is high pressure as a result of sinking dry air as the hadley and ferrel cells meet

  -creates a belt of desert regions eg, sahara desert and desert in namibia (temps exceed 40°c in the day drop to below freezing at night)

• tropical climate:

  -belt of relatively low pressure, heavy rainstorms as a result of rising air in the hadley cell

  -eg, northern brazil in south america, malaysia in south east asia

• polar climate:

  -at the highest altitudes cold air from the polar cell sinks, producing high pressure

  -characterised by dry, icy winds caused by the spin of the earth

  -some places in antarctica reach wind speeds of 50 mph

• temperate climate:

  -in the mid latitudes, 50-60° north and south of the equator, warm and cold air types meet and low pressure is created from the rising of the warm

  -as this air rises and cools it condenses to form clouds and rainfall

what are the extremes in weather associated with temperature?

• coldest area on earth: vostok research station located in east antarctica reached -89°c , it receives very little sunlight and is located at a high altitude

• hottest area on earth: al-aziziyah, libya hottest recorded temp at 58°c, due to the dry climate and onshore winds do not have enough moisture to pick up so as the moisture depleted air falls it creates dry conditions

what are the extremes in weather associated with percipitation?

• driest area on earth: atacama desert, the andes, characterised by coastal mountains blocking pacific and amazonian air, are influenced by east-west winds, creating a rain shadow on the eastern side, resulting in a dry atacama desert- it recieves less than 1mm ppx annually

• wettest area on earth: puerto lopez in columbia receives an annual rainfall of 13,000 mm, this is because there is a constant moist tropical flow from the pacific ocean

what are the extremes in weather associated with wind?

windiest place on earth: commonwealthbay in antarctica experiences winds exceeding 240 km/h, montainous landscapes act as a funnel for winds increasing their speed

what is the distribution and frequency of droughts?

• a drought is a period of time with abnormally dry weather leading to a shortage of water

• droughs commonly occur in central africa and the mediterranean(every continent has them)

• there are more frequent droughts in south east australia and east asia

• there are less droughts in northern europe, west asia and south america

• droughts are becoming worse due to: building cities in arid areas, building dams, over farming and deforestation

• the met office have predicted there will be 10% more droughts in the uk

what is the distribution and frequency of tropical storms?

• a tropical storm begins as a low pressure system originating in the tropics known as a tropical depression- its characterised by high winds and heavy rain

• commonly located along the tropic of cancer

• distributed in south east asia and northern oceania(found over tropical waters between 5-30° north and south of the equator)

• the number of tropical storms has not increased significantly but the intensity has become stronger, the energy released has increased by 70% over the past thirty years

what are the causes of the extreme weather tropical storms produce?

• heavy rain

  -warm, moist air is rising due to the low pressure

• strong winds

  -large pressure differences between the eyewall (low pressure) and the high pressure elsewhere

• storm surge

  -low pressure at the earths surface allows the level of the oceans to rise

what is el niño?

• during el niño, trade winds weaken or stop

• the piled up warmer water around australasia makes its way back eastwards across the pacific leading to a 30cm rise in sea level around peru, this prevents the usual cold upwelling

• as a result there is more warm water over the coast of peru leading to rising air and low pressure, the water becomes 6-8°c warmer in the eastern pacific

• peru experiences more rainfall than normal

• in australasia the water becomes cooler and there is less air rising resulting in dry conditions

what is la niña?

• a la niña event may follow an el niño event

• la niña refers to unusually cold sea surface temperatures found in the eastern tropic pacific

• where australia would experience droughts during el niño there could be a chance of increasing flooding during la niña and peru would experience more droughts when beforehand they experienced more rainfall

what are the causes of the extreme weather conditions of el niño/la niña leading to drought?

• in el niño conditions, air pressure rises in the western pacific and falls in the east this causes the trade winds to reverse so they now blow west to east

• this pushes warm water towards south america preventing the usual cold upwelling

• as a result there’s more warm water over the coast of peru leading to rising air and low pressure

• peru experiences more rainfall however in australia the water becomes cooler leading to less air rising and dry conditions

how is a hurricane formed?

• rising air from warm ocean surface draws water vapor, which cools and condenses to form tall thunder clouds

• as the air rises, it releases heat, causing it to rise even more, smaller thunderstorms form a giant spinning storm, which becomes a tropical storm when surface winds reach 120km/h

• tropical storms can grow to over 300 miles wide, but their wind speeds are high, they travel at around 15mph over the earth's surface, but upon reaching land, they lose energy and weaken

• if they reach warm seas, they can regain strength

background information on the uk-based case study of extreme weather: boscastle floods, cornwall 2004

• boscastle experienced a flashflood (sudden localised flood due to heavy rain that falls too fast for the ground or drains to absorb)

• boscastle is a village in north cornwall, it experienced a flashflood on the 16th august 2004 where it received 70mm of rain in 2 hours

causes of the boscastle floods

• natural causes:

  -topography: steep hills and small narrow valleys meant the water was funnelled through boscastle

  -river was flowing 40 mph

  -there had been above average rainfall for the past 2 weeks which meant the ground had already become saturated, any later rainfall became surface run off flowing straight into the river

• human causes:

  -the pattern of the streets (eg, main street running down the bottom of the valley) made it worse

  -cars became trapped under the low-lying bridge through the village, this acted as a dam and water quickly found an alternative route around the bridge causing more damage to the village and its buildings

consequences of the boscastle floods

• environmental:

  -trees washed away

  -lots of soil erosion

  -animal habitats destroyed

• economic:

  -houses and vehicles destroyed

  -increased tourism

  -harbour light (oldest building) destroyed

  -20 bnbs were shut down

  -over £2 billion worth of damage to roads

  -25 businesses were destroyed including the witchcraft museum

• social:

  -6 people were injured and taken to hospital

  -worst injury was someone lost a thumb

  -people lost jobs as buildings were destroyed

  -84 cars recovered from the sea, 32 never found

responses to the boscastle floods

• short-term: (from RAF)

  -7 helicopters rescued people from roofs

  -120 people were picked up and taken to safety

  -local residents used sand bags to stop water entering houses

• long-term:

  -built flood defences, river valency was deepened and widened

  →culvert channels meant in the event of a flood water would return to the ocean

  -£10 million was spent on defence

  -new sewage system installed

background information on the non uk-based case study of extreme weather: the big dry

• the big dry (2002-09) was the driest period for 125 years

• bundurra received 10mm of rainfall per month compared to the average 50-80mm (annual ppx of 767mm)

• highest temp it reached was 36°c

causes of the big dry

• natural:

  -during el niño the trade winds over the pacific ocean weaken, less warm water is brought from south america so the sea water cools and rainfall diminishes

  -australia is located in a sub-tropical area of the world that experiences dry, sinking air leading to clear skies and little rain

• human:

  -the murray-darling river basin covers part of new south wales, victoria, queensland and south australia

  -it is home to over 2 million people and there is a lot of pressure on the river basin to provide the water needed to support agriculture in the region

  -over population has resulted in more pressure on water supplies

consequences of the big dry

• environmental:

  -energy produced from hydroelectric power was reduced leading to more pollution as australia resorted to fossil fuel use

  -the big dry included loss of vegetation, wildlife and biodiversity

  -soil erosion increased and grassland turned to scrubland

  -water quality reduced as toxic algae outbreaks occurred in depleted rivers, dams and lakes

• economic:

  -farmers having to sell their cattle as they couldn’t afford to feed them

  -food prices increased as they required more exports

  -water bills rose by 20% in 2008

  -tourism was negatively impacted

  -agricultural production sharply dropped

• social:

  -dairy farms reduced by more than half

  -10,000 people directly employed by the cotton industry were affected

  -the big dry caused rural-urban migration which put greater pressure on the cities

  -rural suicide rates increased

responses to the big dry

• short-term:

  -farmers were supported with payments of $400-600 in assistance from the government per fortnight

• long-term:

  -recycling waste water from showers, baths, wash basins and washing machines known as greywater was encouraged

  -water storage tanks for homes were subsidised and states introduced “drought-proofing”

  -more efficient irrigation systems were installed and a new multimillion-dollar destination plant was built in sydney

  -government was paying out $1.7 million a day in drought relief to farmers

  -laws were created to ban car washing and limiting showers to 4 minutes

  -states were urged to hand the responsibilites for managing the basin to the government

why do tectonic plates move?

• the crust moves because of the movements deep inside the earth

• heat rising + falling inside the mantle creates convection currents generated by radioactive decay in the core

• the convection currents move the plates

• where convection currents diverge near the earth’s crust, plates move apart, where convection currents converge, plates move towards eachother

• the movement of the plates, and the activity inside the earth is called plate tectonics

• plate tectonics cause earthquakes and volcanoes

describe and compare the pattern of earthquakes and volcanoes

• on the pacific plate boundaries, a large amount of volcanic and earthquake hazards occur

• on the convergent eurasian, south and north american plate boundary many major volcanic and earthquake hazards occur

• however volcanic hazards can occur in countries not located on destructive or collision boundaries eg, hawaii

what is the structure of the earth?

• the crust:

  -outer layer of earth

  -8-65km thick

  -made up of granite and basalt (light)

• the mantle

  -forms about half of the earth

  -it is 1,200°c

  -solid next to the crust, liquid next to the core

• the inner core

  -it is very solid

  -very hot: 5,500°c

  -made up of iron and nickel (heavy)

• the outer core

  -it is liquid

  -it is 3,700°c

  -made up of iron and nickel (heavy)

what are the differences between the continental and oceanic crust?

• the continental crust is 25-100km thick, less dense, older and is a mixture of all rock types(sedimentary, igneous and metamorphic)

• the oceanic crust is 5-10km thick, denser, younger and mainly igneous rock eg, basalt

how are hotspot volcanoes formed?

• hotspot volcanoes form above plumes of hot magma called hotspots

• a hotspot is formed when an oceanic plate moves over a hot area of the mantle, which creates a super-heated plume of magma rising up towards the crust

• eventually, this can punch through and when the plate becomes heated enough the magma will erupt to the surface, this leads to a chain of volcanic islands appearing eg, hawaii and azores

• the further away from a hotspot an island is, the older it is

what happens at a constructive plate boundary?

• at a divergent constructive plate boundary, the plates are moving apart

• this type of movement mostly happens under the oceans

• the gap left is filled by magma rising up from the mantle below to form volcanoes and new crust

• some volcanoes have grown high enough to form volcanic islands such as hawaii and iceland

what happens at a destructive plate boundary?

• at a convergent destructive plate boundary, the plates are moving together

• the denser oceanic crust sinks below the lighter continental crust

• the oceanic crust sinks into the mantle and it melts in the subduction zone

• energy is released by the movement which may be felt on the surface as an earthquake

• the molten rock called magma may rise upwards causing a volcanic eruption

• these may be found around the pacific ocean and up the west coast of south america

what happens at a conservative plate boundary?

• here the plates are sliding past each other

• the line of weakness where the two plates meet is known as a fault

• pressure builds up until the two plates can slide past each other

• this causes an earthquake and the land around it becomes crumpled and ridged, a good example is the san andreas fault in california

what happens at a collision plate boundary?

• at a convergent destructive plate boundary, if the two plates are both continental crust, because the crust is less dense it cannot sink downwards so the rocks between them are forced upwards

• the continental crust is crumpled up into fold mountains

• a good example is the himalayas where the austral-indian plate collided with the eurasian plate

explain how the movement of plates causes earthquakes

• tectonic plates are not smooth, they are jagged and rocky

• the edges grind together and stick, this creates stress and friction between the plates, this friction causes a build up of potential energy, which will eventually overcome friction and cause the rocks to jolt/slip and move

• this sudden movement releases energy through seismic waves, these radiate out like shockwaves through the rock

• the shockwaves spread out from the focus (the point in the earth where the earthquake starts)

  →near the focus the waves are stronger and cause more damage

• the epicentre is the point on the earth’s surface directly above the focus

• shallow focus earthquakes tend to produce more damage than deep focus earthquakes as the shockwaves have to pass through less crust to reach the surface

what are the two ways you can measure earthquakes?

• richter scale:

  -measures the energy of an earthquake

  -the scale is logarithmic which means that every jump up the scale you get a 10x increase in shaking amplitude, the higher the magnitude the less frequent they are

• mercalli scale:

  -measures the effects of an earthquake and runs from a scale of 1-12

  -the higher up the scale the more damage is experienced by people and buildings

  -the first 6 levels on the scale reflect mainly the impacts on people and the last 6 levels relect impacts on buildings and infrastructure

what are the primary and secondary effects of an earthquake?

• primary: happens immediately as the earthquake shakes the ground

  -people are injured or killed by collapsing buildings and falling debris

  -electricity cables, gaswater pipes, communication networks and sewage infrastructure are damaged

• secondary: happens after the earthquake has happened

  -repair and construction can be very costly and so can weaken a country’s economy

  -people are left homeless and could die from the cold or exposure

how are volcanoes formed?

• tensional (constructive): shield volcano

  -as the plates move apart, magma rises upwards from the mantle to fill the gap, this adds a new rock to the spreading plates, some of the magma may also be forced out to the surface through a vent, some volcanoes grow high enough to form volcanic islands

  -characteristics include: cone with wide base and gentle slope, made of lava only, regular with frequent eruptions, lava pours out with little violence eg, mauna loa, hawaii

• compressional (destructive): composite volcano

  -when the plates collide, the denser oceanic plate is pushed down into the mantle, here the plate melts and is destroyed in the subduction zone, in the subduction zone the plate forms a pool of magma, the great heat and pressure may force the magma along a crack where it erupts at the surface to build up a volcano

  -characteristics include: tall cone with narrow base and steep sides, made of alternate layers of lava and ash, irregular with dormant periods, violent explosions possible eg, etna, italy

what is the vei?

• vei (volcanic explosivity index)

• It’s a 0-8 log scale

• it assesses how far the ash plume travelled, the volume of material ejected and how often that type of eruption occurs

background facts on e15

• the erruption occurred on the 15th april 2010

  →continued intermittenly until the 21st when the lava stopped and only steam was released, it was declared over on the 28th october

• a level 4 on vei

• carried the ash 9km into the atmosphere

• iceland is an island created by volcanic activity and sits along a constructive plate boundary

• e15 is an ice cap covering a gently sloping volcano

causes of e15

• the island sits along a constructive plate boundary between the north american and eurasian plates

• these plates are moving apart at the mid-atlantic ridge

• the magma chamber under the volcano filled up, pressure increased and magma rose towards small cracks

• the lava erupted as fire fountains initially but after 2 weeks another source of magma from the mantle rose up more viscous and explosive

consequences of e15

• environmental:

  -flooding: heat from the eruption melted vast amounts of ice underneath the icecap

  -the glaciers were covered in dark ash which increased melting

  -200m of ice melted and caused a flood

• economic:

  -disruption to farming: in order to stop livestock eating grass or drinking water poisioned by ash farmers had to keep animals indoors

  -20 farms were destroyed

  -increased spending by tourists stranded away

  -ground air cargo flights stopped delivery of items such as food, flowers, medicines and mail

• social:

  -airport closure: keflavik airport from the 23rd of april was shut for several days

  -95,000 flights were cancelled across europe

  -there were some respiratory problems as ash settled in the lungs of humans and animals

responses to e15

• short-term:

  -iceland has a well trained national emergency agency which coordinates recovery and response tactics eg, replacing bridges immediately with temporary pre-built structures

  -putting animals inside to stop them eating grass poisoned by ash

  -two sections of route 1 were destroyed to allow the glacier to escape and not destroy the road

• long-term:

  -iceland has spent a lot of money on technology to detect eruptions such as thermal cameras and satellite imagery

  -put a local text message warning system into place

  -having volcano insurance for travel

what are some mitigation strategies for volcanoes?

mitigation- actions to make something less severe:

• emergency text message alert system

• spectometer to measure the build up of gases such as sulphur dioxide which is one of the driving forces of a volcanic eruption

• soil or water ph become more acidic as the sulphur content increases

• lahar sensors to measure earthquake activity as it increases prior to a volcano as magma and gas force their way up towards the surface

how would you plan for a volcano?

• pack an emergency kit including: medicines, food, flares, a first aid kit, sleeping bag

• make sure you know protocol:

  -listen to alerts

  -follow evacuation orders from local authority

  -avoid areas downward of the volcano

  -take temporary shelter from the volcanic ash

how would you prepare for a volcano?

• secure furniture so it can’t fall over or fall down

• plan safety measures to avoid injuries

• confirm the strength of your house and walls

• always be ready to extinguish fires

• take steps for fire prevention and early detection

• prepare emergency supplies