Geography - Global Hazards

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  • Created by: Riya.b123
  • Created on: 09-02-19 14:34

Winds

- are large scale movements of air caused by differences in air pressure which is caused by differences in temperature between equator and the poles.

- move from areas of high to areas of low pressure.

- part of global atmospheric circulation loops.

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What are the different climate zones around the wo

- Polar - Temperatures low all year.

- Temperate - Moderate summers & winters, low pressure belt caused by rising air, frequent rainfall.

- Tropical - Hot all the time, high rainfall, usually near equator.

- Arid (dry) - Low rainfall most of the year.

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Extreme Winds

- Global Atmospheric Circulation makes some parts of the world winder than others.

- Weak in high & low pressure belts.

- Strong between pressure belts.

- Can be extremely strong when differences in between high & low pressure areas is large.

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Extreme Precipitation

- Ocurrs when warm, wet air rises and cools.

- Air rises in low pressure belts meaning rainfall is frequent & intense e.g rainforests (The Amazon).

- Extremely low in high pressure belts e.g. Sahara Desert.

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Extreme Temperatures

- Equator receives most energy from sun.

- Very high in high pressure areas - little clouds to block sun's energy.

- in polar regions temperature is very low. 

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Australia's weather compared to the UK's

- Australia - warmer than UK, hot summers & milder winters.

- Average summer temp - 33, over 40 extremely hot.

- London - Average summer temp - 23, over 30 extremely hot.

- Australia - much lower precipitation (465 mm) - Extreme (760 mm)

- UK has twice as much rainfall (1154 mm) - Extreme (1337 mm)

- Australia has stronger extreme winds than UK.

- Australia affected by tropical cyclones.

- Gales are rare in the UK.

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What are tropical storms and what do they do?

- Intense low pressure weather systems with heavy rain & strong winds that spiral around at centre. 

- Bring extreme weather conditions.

- Develop when sea temp is 27C or higher - warm ocean - warm moist air to cause precipitation.

- Condensation makes is powerful.

- Earth's rotation causes storm to spin.

- Storm gets stronger from energy from warm water - wind speeds increase (250km/h or more) - Damage & destroy buildings & plants. 

- Flooding & mudslides.

- Most occur north & south of equator - majority in northern hemisphere. 

- Number of tropical storms in Atlantic increased since 1984.

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El Nino

- Air & ocean currents change in the Pacific ocean.

- Every 3-4 years - weaken or reverse..

- Last for 9-12 months

- Pressure rises in Western Pacific - falls in East.

- Trades winds to weaken or reverse.

- Sinking air in Western Pacific leads to dry weather. (Drought)

- Rising air in Eastern Pacific - wet weather

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La Nina

- Normal conditions become extreme.

- Trade winds move to West strongly 

- Cold water rises in Eastern Pacific

- Heavy rainfall & floods in West

- Less rainfall & droughts in East

- Occur 2-7 years

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What is a drought & how is it caused?

- Long period when rainfall is below average

- Water supplies become depleted - people use them

- High temperatures increase rate of evaporation.

- High pressure weather system blocks depressions

- Areas most at risk - Central & Southern Africa, Middle East etc..

- Since 1950 - more droughts in Africa, Asia

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Bostcastle Flash Food - 2004

- 75 mm rain fell in 2 hours.

- Lots of rain in previous weeks - ground could not absorb water

- Steep-sided valley - surface water ran into river channels quickly

- Old bridge - low arch - trees & vehicles trapped under.

- 58 properties, 4 businesses, roads destroyed, 50 cars underwater

- People couldn't evacuate - sudden  

- Tourism dropped - 90% economy relied on it.

- 100 airlifted to safety, temporary accomodations, bridge rebuilt with higher arch

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Hurricane Katrina

- Tropical storm struck South-East USA

- Storm travelled over Gulf of Mexico - got stronger

- 1800 people killed, 300,000 houses destroyed - 80% New Orleans flooded, 3 million wothout electricity. 

- Coastal habitats destroyed

- 230,000 jobs destroyed, water supplies polluted with sewage & chemicals. 

- 70-80% Orleans residents evcuated 

- over 50,000 people rescued 

- US governemnt spend over $16 billion rebuilding homes.

- Repaired & improved flood defences.

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2003 - Heatwave

- Long period during which temperature is much higher than usual.

- Caused when anti-cyclones stay in the same place.

- Temperatures in UK higher than normal. 

- People suffered from heat strokes, dehydration etc. 

- 2000 died, 20 injured

- Livestock died - trains buckled & melted

- NHS & media gave guidance to cope

- Limitations on water use

- Speed limits on trains

- UK created "Heat Wave Plan"

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Millennium Drought - Australia

- From 2001 - 2009

- Naturally had low rainfall due to global atmospheric circulation.

- Low rainfall in South-East Australia

- Climate change may have contributed

- Temperatures higher than normal

- Water levels fell

- Large impacts on farming - crop yields fell

- Vegetation loss & soil erosion

- Water conservation measures introduced

- Desalination plants

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Describe the Earth's Structure

- Earth's surface (crust) split up into tectonics.

- Oceanic crust - thin & dense

- Continental crust - thick & less dense

- At centre is the core

- Inner core - solid iron & nickel

- Outer core - liquid

- Mantle around core - semi molten rock

 

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Convection Currents & Plate Margins

- Tectonics move due to convenction currents in the mantle 

- Low parts of mantle sometimes hotter than upper parts and become less dense & slowly rise

- Move towards top of mantle & cool down - more dense - slowly sink. 

- Place where plates meet are called plate boundaries or plate margins.

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What are the 4 different plate boundaries?

- Destructive - oceanic plate moves toward continental plate, dense oceanic plate forced into mantle - creates volcanoes & ocean trenches.

- Collision - both continental crust move towards each other, plates forced upwards - fold mountains

- Constructive - 2 plates move away from each other - magma rises & cools - new crust

- Conservative - 2 plates move sideways past each other - same direction - different speeds. Crust isn't created or destroyed. 

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Earthquakes

- Caused by tension that builds up at all plate boundaries. 

- Plates send shock waves (earthquake) - spread out from focus

- Waves stronger near focus - more damage

- Measured in magnitude (Mercalli Scale - effect), Richter scale (energy released) 

- Shallow focus earthquake - more damage, deep focus - less damage

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Volcanoes

- Found at destructive & constructive plate margins

- Emit lava & gases & ash, form pyroclastic flows

- Volcanic activity occurs at plate boundaries

- Hotspots - intense volcanic actvity not at any plate boundaries (Earth' s crust hotter than normal)

- Composite Volcanoes - at destructive PB, steep sided, erupts thick lava, deposits layer of ash. 

- Sheild Volcanoes - at hotspots or constructive PB, not very explosive, flows quickly, low gentle sided. 

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Pakistan Earthquake 2005

- Eurasion plate & Indian plate meet at collision PB. 

- Area prone to seismic activity

- 80,000 deaths - from collapsed buildings, 10,000 injured

- Water & electricity pipelines damaged

- Disease spread

- International aid from other countries

- Medical supplies distributed

- Government money to rebuild homes

- 40,000 to new settlement 

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How to manage impacts of tectonic hazards?

- Early Warning Systems for earthquakes - warnings can be communicated quickly to people when shaking detected. Useful - get under cover quickly

- Predicting & monitering volcanoes - gives time for evacuation, reduces number of deaths & injuries. Seismometers can detect indications of eruption. 

- Building design - earthquake/volcano resistant buildings, special foundations, specialsied pipeliness. 

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