3 - Hazardous environments

Tropical cyclone characteristics

• Rotating, low pressure system (<950mb)

• Known as hurricanes, cyclones + typhoons in different areas of world

• Heavy rain

• High wind speed (>119kph)

• High waves + storm surges

• Calm, clear eye

Tropical cyclone distribution

• Tropical regions

• 5-30° N and S of equator

• Sea temp > 27°C

Tropical cyclone measurement

Saffir-Simpson scale, 1-5 rating based on max sustained wind speed

Tropical cyclone causes

• Low pressure areas (<950mb) - air rises faster to fill low pressure area, so speed of cyclone increases

• Sea surface temp >27°C - warm air rises, forming low pressure area underneath for more air to rush in

• Between 5-20° N and S of equator

• Low wind shear - change in wind speed with height: upper level winds stronger, resulting in destruction of storm’s structure

• Coriolis force - rotation of Earth around its axis causes cyclones to rotate opposite direction + be deflected from their path

Tropical cyclone formation

• Warm, moist air rapidly rises forming area of low pressure

• Air from high pressure areas rushes in to take place of rising air

• Air rises forming continuous flow of rising air

• As air rises, it cools + condenses, releasing heat energy to help power cyclone

• Air at top of storm goes outwards away from centre of storm

• Coriolis force causes rising air to spiral around centre

• Some air sinks in middle, forming cloudless, calm eye

• Cyclone moves westwards from source

• When cyclone makes landfall, no longer has supply of warm, moist air so loses speed + temp

Tropical cyclone case study

Typhoon Haiyan, Philippines, 2013

Short-term impacts:

• 7000 killed, 1.9m homeless, 6m displaced

• Disease outbreaks due to lack of sanitation, food, water, shelter, medication

Long-term impacts:

• Estimated economic impact = $5.8bn

• City of Tacloban’s airport severely damaged, affecting business + tourism

Earthquake characteristics

• Sudden, violent shaking of ground

• Focus (underground) - origin of seismic waves

• Epicentre (surface) - point directly above focus

• Secondary hazards:

  • Liquefaction: wet soil is shaken; water from soil rises + turns soil into liquid mud, can cause buildings to fall

  • Landslides

  • Fires

  • Tsunamis

Earthquake distribution

• Shores of Pacific Ocean

• Many in Atlantic, Indian + Pacific Oceans

• Along plate boundaries/hotspots

Earthquake measurement

Magnitude:

• Richter (logarithmic)

• Moment Magnitude - measures amount of energy released (for every 1.0 amount of energy increases by 30x + amplitude increases by 10x)

Intensity:

• Mercalli - measures amount of damage caused

Earthquake causes

• Mostly at plate boundaries

• Occur at all plate boundaries: convergent, destructive, collision, conservative

• Weaker at constructive boundaries as plates moving apart

• Stronger at destructive, conservative + collision boundaries

Earthquake impacts case study (developed)

Tohoku, Japan, 2011

Short-term:

• Land subsidence in coastal areas as EQ dropped beachfronts by 50cm+

• 9m wave flooded plants, generators + electrical wiring - people lost energy immediately

• 4.4m households in N East Japan left without electricity

Long-term:

• Economic cost = $235bn (most expensive disaster in history)

• Damaged caused by EQ resulted in meltdown of 7 reactors. Radiation levels 8x the normal.

• Japan’s transport network suffered huge disruption. Sections of Tohoku Expressway damaged.

Earthquake management case study (developed)

Tohoku, Japan, 2011

Preparation:

• EQ + tsunami training drills for mag. 6 triggered tsunamis

• Cross bracing in skyscrapers + flexible pistons to absorb shock → buildings sway, not crumble

Short-term relief:

• 200,000 ppl evacuated from near Fukushima power plant

• 20km exclusion zone around Fukushima

Long-term response:

• Projects to improve roads, railways + airports

• Start to invest in renewable energy due to risk of nuclear plants

Earthquake management case study (developing)

Haiti, 2010

Preparation:

• Very little - only 1 malfunctional seismometer

Short-term relief:

• Many countries sent people to help (medical search + rescue, food + water)

• Many US troops flew over to distribute aid

• Mass graves filled with bodies to get them off streets + prevent spread of disease

Long-term response:

• World Bank cancelled half of Haiti’s debt + gave 5yr payment holiday on remaining half

• More health workers trained + given incentives to stay in Haiti

• New settlements built away from high-risk locations

General earthquake preparation methods

• Early warning systems: if EQ detected, warn people before ground shakes

• Building design: retrofitting, cross-bracing

• Geographic Info Systems (GIS): mapped info about prev. EQs - vulnerable areas, transport access etc. to prepare more effectively

• Remote sensing: satellite images used for EQ info e.g. damage caused, access problems, helping prepare for future EQs in that location

• Education + EQ drills: practice ‘drop, cover, hold on’, keep important supplies in EQ kit, fix heavy furniture to wall

General short-term relief methods

• Evacuation

• Temporary shelters

• Exclusion zones

• Provide food, water, medical care

General long-term response methods

• Hazard mapping

• Risk assessment

• Improve infrastructure

• Change building regulations to combat EQs

Volcano characteristics

• Magma chamber

• Lava flow - stream of molten rock

• Pyroclastic flow - mixture of rock, gas, ash that travels rapidly (high temp + mobility)

• Lahar - mudflow created when rainwater + volcanic ash mix

Volcano distribution

• Mostly on plate boundaries

• ‘Pacific Ring of Fire’ - concentration of volcanoes along destructive margins around Pacific

Volcano measurement

Volcanic Explosivity Index (VEI): 1-8 based on amount of material ejected, height of cloud + damage caused

Volcano causes

• Occur at constructive, destructive + hotspots

• Not at conservative or collision

How volcanoes form at constructive boundaries

• Plates moving away from each other

• Constructive boundaries often under sea

• Lava escapes through gap left when plates move away

• Lava cools + hardens forming new crust

• Lava is runny + eruptions less explosive

• Forms shield volcanoes with gently sloping sides

How volcanoes form at destructive boundaries

• Plates move towards each other

• Heavier, denser oceanic plate subducts under lighter continental plate

• In subduction zone, plates come together causing friction

• Friction causes heat + plate material melts forming magma

• Magma rises to surface through cracks in crust

• Cooling lava + ash builds up, forming volcano

• Lava is sticky + explosive eruptions

• Forms composite/stratovolcanoes

How volcanoes form at hotspots

• Tectonic plate passes over magma plume

• Magma rises to surface through cracks in crust

Volcano case study

Montserrat, 1995-2013

Short term impacts:

• 1997 - pyroclastic flow killed 19 people

• Largest settlement, Plymouth (4000 pop.) was covered in ash and abandoned

• 75% of island covered in ash

Long term impacts:

• High level of unemployment (>50%)

• Population decreased by 90%

• Housing shortages leading to 70% increase in rent

Constructive plate boundary

• Two oceanic plates ← →

• Magma rises to fill gap + turns into solid rock as it cools

• New crust forms mid-ocean ridge

• Both volcanoes + EQs here (caused by movement of magma through crust)

• e.g. Mid-Atlantic Ridge

Destructive plate boundary

• Oceanic + continental plate → ← due to convection currents in mantle

• Denser, heavier oceanic plate subducts under lighter continental plate

• Both volcanoes + EQs here (caused by friction of plates, when one slips past other, releases seismic energy)

• e.g. Nazca + S American plates

Collision plate boundary

• Two continental plates → ←

• Neither is dense enough to subduct so land pushed upwards

• Forms fold mountains

• Mainly EQs here

• e.g. Himalayas

Conservative plate boundary

• Two continental plates ⇆

• Plates move past at diff speeds in opposite directions

• Friction causes EQs

• e.g. San Andreas Fault

Why people live in areas at risk from volcanoes

• Minerals - valuable mineral resources such as diamonds, gold, copper emerge during eruptions

• Fertile soil - volcanic ash contains mineral that enrich soil

• Geothermal energy - water running through earth’s crust is heated by volcanic rock at plate margin. Hot water emerges as hot springs: can be used to heat homes, factories, business premises.

• Tourism - volcanoes interest many people + attract tourists
  e.g. Mount Vesuvius: hundreds of thousands of visitors each year

Reasons people live in areas at risk from natural hazards

• Lack of education + info - people unaware of real risks, particularly in poor, undeveloped areas

• People aware of risks but live there anyway - area may offer attractive benefits

• People unable to move away from hazardous areas due to lack of money, being worried they won’t find a job elsewhere or they’re settled/have family

• Cities in high-risk areas represent centuries of investment (human money + effort) - no society is rich enough to throw away all this investment and abandon those cities

Physical factors affecting vulnerability to natural hazards

• Global location - some areas experience more hazards because they’re near plate boundaries/in tropical regions

• Physical environment - steep slopes can increase chances of landslides; coastal areas more vulnerable to storm surges + tsunami

Social factors affecting vulnerability to natural hazards

• Pop. density - more people in area = higher number of deaths + injuries. High pop. density also means buildings are likely to be more densely packed.

• Education - people with higher level of education likely to be wealthier + able to afford better-quality housing. Education level also affects how informed people are about risks.

Economic factors affecting vulnerability to natural hazards

• Wealth + level of development - quality of buildings, healthcare, infrastructure depend on wealth of country

• Insurance - people in poverty can’t afford insurance + insurance companies only insure well-built homes/structures

• Buildings - planning control, poverty, building styles, quality of materials affect safety of buildings

• Technology - wealthier countries have more access to monitoring equipment so may get better warning of events