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Define earthquake
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Define earthquake
A release of pressure when two plates slip past each other suddenly sending out shocks or seismic waves
Earthquake: where
Plate boundaries
Earthquake: why
Forces in the earth slowly build up until they exceed the factors impeding fault motion causing sudden slip on the fault
Earthquake: convergent
When plates meet, friction causing pressure to build up creates earthquakes
Earthquake: divergent
When plates are pulled apart and are weakened and fractured, the tensional build up of pressure creates earthquakes
Richter Scale (magnitude)
A logarithmic scale for measuring the degree of shaking or number of oscillations
Mercalli Scale (intensity)
A scale that uses observations of people who experienced the earthquake
Earthquake: ground shaking
The longer the ground shakes (severity affected by strength, distance from epicentre, local geological conditions) the more damage caused, such as causing buildings to collapse and kill people
Earthquake: landslides, rock and snowavalanches
Occurs in mountainous areas where slops are weakened by strong shaking and eventually give way, landslides may block roads and access routes
Earthquake: tsunamis
Occurs when earthquakes are beneath the sea and send seismic waves that travel very fast and cause destruction along the coast and very rapid flooding
Earthquake: liquefactionShock waves cause groundwater to rise to the surface turning soft ground to mud, any buildings built on clay may sink into the mud and collapseEarthquake: building safetyShear wall (reinforced concrete walls - strength and resist rocking), shear core (reinforced concrete - strong core), cross bracing (diagonal steel bars reinforce walls), base isolator (shock absorbers made from alternating steel and rubber, dampen impact up and down/side to side)Earthquake: land use planning and regulation"Red" high risk zones are avoided when planning building locations, "amber" mild risk ones allow buildings but with careful regulations and restrictions (e.g. one storey only, buildings far apart), "green" little to no risk zones allow planning agencies to build houses in any wayEarthquake: warning systemsScientists monitor active zones using sensitive instruments (measuring earth movement) to produce maps of earthquake probability or to give early warning of tsunamis, foreshocks occur before some large earthquakes, number of recent earthquakes are plotted to show if a major earthquake can be expectedEarthquake: population densityIn denser regions, there are more people in range of the earthquake so more people affected and there may be insufficient healthcare for everyone, and greater building density which are more vulnerable to collapseEarthquake: magnitudeA larger magnitude means it may be more violent so more damage is caused to buildings and more people dieEarthquake: wealth of regionIn poorer regions, local healthcare is poor, buildings are unstable, sanitation is poor so diseases spread, and people are often unpreparedEarthquake: time of dayIn the day, people are active and can respond more quickly by leaving the building BUT at night, people are sleeping and indoors so react slower or not all so buildings collapse on themEarthquake: under water?An underwater earthquake can spread over a further distance and cause tsunamis to destroy coastal cities, on land it may have less range and less people dieEarthquake: yearIn the present day, people are more likely to have the resources and understanding of what to do during earthquakesEarthquake: accessibilityIn isolated regions, it may take longer for aid to arrive or for signals for help to reach cities and so more people dieEarthquake: geologyOn consolidated surfaces, seismic waves remain at the same amplitude BUT on unconsolidated surfaces, seismic waves are amplified as particles... on each other, so there is greater damage and more people dieDestructive margin (subduction zone)When convection currents come together where an oceanic plate and continental plate meet, they collide as the denser oceanic plate submerges under the bouyant continental plate (point where this happens: subduction zone), forming a deep sea trench in the oceanExample of destructive marginNazca and South American - AndesCollision marginWhen convection currents come together where two continental plates meet, they collide and because neither plate is denser, the edges are forced upwards, forming fold mountainsExample of collision marginIndo-Australian and Eurasian - HimalayasDivergent marginWhen convection currents move away from each other where two plates meet, plates move apart, weakening and typically breaking along faults, gap allows magma to seep upwards and form new crust when it hardens into rockDivergent margin: rift valleyAs sides of the rift move apart, central sections drop down to form rift valleys (e.g. Great East African Rift Vlley)Example of divergent marginMid-Atlantic ridgeTransform marginWhen convection currents move in opposite directions parallel to two plates, the plates past each other, causing pressure to built up due to friction, causing earthquakesExample of transform marginSan Andreas fault, Pacific Coast of USABasic lava (constructive margin) featuresEffusive, runny, low viscosity, 1200 degrees, hotspot, shield volcano (layers of lava) with low gradient and large areaBasic lava hazardsPrimary: LAVA, gas, ash, secondary: poisoned water, fireExample of basic lava volcanoMauna Loa, Hawaii (North American and Eurasian)Acid lava (destructive margin) featuresExplosive, thick, high viscosity, 800 degrees, subduction zone, stratovolcano (alterating layers of lava and tephra)Acid lava hazardsPrimary: PYROCLASTIC flows, tephra, ash, gas and landslides, secondary: tsunamis, mudflows (lahars), poisoned waterExample of acid lava volcanoMount Etna, Sicily (African and Eurasian)Volcano: wherePlate margins (destructive and constructive)Volcano: how (convergent)When plates converge in subduction ones, FRICTION generates a lot of HEAT, causing the plate to dehydrate and melt, MAGMA RISES from a magama chamber as ACID LAVA, which is gaseous, thick and cools quickly, blocking its own path to the surface and causing pressure to buildVolcano: laharsPyroclastic flows mixed with waterVolcano: how (divergent)When plates diverge, crust is weakened and FRACTURES as it is pulled apart by convection currents, MAGMA RISES trough these faults as BASIC LAVAVolcano: hotspotsWhen a plate moves over an especially hot part of the mantle where a plume of hot material (the further away, the older the volcano)Volcano: geothermal energyUsing underground steam resources that have been heated up by the Earth's magmaVolcano: fertile soilAreas near volcanoes contain mineral rich soils, ideal for farmingVolcano: tourismCreates jobs including hotels, restuarants, gift shops and tour guidingVolcano: miningLava contains minerals that can be mined once lava cools, mining towns provide jobs, volcanic rock is a good building stoneVolcano: seismographDetects vibrations when magma rises towards the surface, any sudden activity give scientists time to sound warningsVolcano: ground deformationAs magma rises, it has to make space for itself so the ground bulges which can be detected by sensitive GPS instrumentsVolcano: gasesChanges indicate possible eruptionVolcano: discharge of waterChanges including density indicate possible imminent eruptionsDrought: whereBetween tropics (hotter, drier climate) towards the centre of large continentsDrought: anticyclone weatherProlonged period of high pressure, air holds less moisture, less rainfallDrought: global warmingWeather patterns changingDrought: hotter weatherEvaporation > precipitationDrought: el ninoRandom weather event reverses normal weather patternsDrought: sea temperatureA cool sea temp means water is less likely to evaporateDrought: overpopulationToo many people use up too much waterDrought: overcultivationGrowing too many crops so soil becomes infertileDrought: overextractionRemoving too much groundwater for farming so rivers dry up/water table fallsDrought: deforestationRemoving trees (which store water and hold soil together) so land exposed to erosionDrought: overgrazingRearing too many cattle so loss of vegetation and soil erosionDrought: politicsFighting over water or companies being greedy and sell water for profit, war or civil war prevents movement of people so they cannot get to water sourcesDrought: social impacts in LEDCsMany subsistence workers so droughts cause devastation for individual families who rely on one source of incomeDrought: social impacts in MEDCsDemand for water is greater as there are many different industries so affect more peopleDrought: economic impacts in LEDCsLess $ so cannot afford the resources the cope with droughts (cannot build wells or reservoirs) so more severe or prolonged water shortageDrought: economic impacts in MEDCsMore $ so can afford drought response schemes, supplying and storing water BUT use taxpayers' moneyDrought: climatic impacts in LEDCsLow rainfall so droughts, more $ spent on resolving droughts rather than on development, lowering Q of LDrought: climatic impacts in MEDCsLow rainfall so droughts, making land look exhausted, less tourism and need to invest in technology to secure water supplyDrought: political impacts in LEDCsHardship implementing to control use of water, corrupt governments or companies may take advantage of local people and use limited water unfairlyDrought: political impacts in MEDCsPeople can leave or migrate area with drought, so population declinesDrought: technological impacts in LEDCsLimited technology to deal with drought, affecting ability to store and supply water, prolongs water shortageDrought: technological impacts in MEDCsModern and advanced technology help allow countries to cope with droughts, but cost $Drought: use and users impacts in LEDCsSubsistence workers rely on rainwater for cooking, cleaning, drinking so drought lowers Q of LDrought: use and users impacts in MEDCsMore demand so affects more peopleDrought: benefitsWell drilling business, reservoir builders, bottled water companiesDrought: sufferFarmers, residents, government, restaurant workers and ownersSoil erosionTop layer of soil is exposed and is blown away by wind or washed away by rain (isolated heavy rain)DesertificationThe degradation of land in arid and semi-arid areas resulting primarily from human activities and influenced by climatic variationDrought: low tech responsesBuild low walls (built across fields to reduce runoff), areas created for tree planting (to conserve moisture in soil), using microdams/sand dams (to store water which can be used to irrigate farmland), using stone piles (used to irrigate farmland), planting drought-resistant crops (that withstand lack of water)Drought: high tech responsesDrip and sprinkle irrigation (focus water of small area where most useful/doesn't waste water which would flow again), use of concrete water coolers (to utilise hot groundwater), dig wells (to reach underground water) and reservoirs (to save water for future use), cloud seeding, desalination plant (remove salt from water)Drought: cloud seedingInjecting clouds with 'seeds' of silver iodide, salt or dry ice to make the cloud water or ice particles to evaporate sea water and produce freshwater for irrigationDrought: normalCool currents off Peru, East Pacific warmer than West Pacific, strong trade winds, moisture falls over AustraliaDrought: El NinoWarm currents off Peru, East and West Pacific waters at similar temps, weak trade winds, less omisure reaches AustraliaTropical storm: conditions27 degrees sea temp, 60m depth, between the tropics (e.g. carribean and central america, south asia, indian subcontinent)Tropical storm: Atlantic oceanHurricanes hits Caribbean and USATropical storm: Indian oceanCyclones hits India and AfricaTropical storm: WN Pacific OcaenTyphoons hits Japan and IndonesiaTropical storm: WS Pacific OceanWilly willies hits AustraliaTropical storm: problems (3)Heavy rain, strong wind, storm surge (rising of sea)Tropical storm: 1Under these conditions, water from the ocean EVAPORATES rapidly, hot water vapour rises and CONDENSES at dewpoint, forming CLOUDS ("cumulonimbus" large cloud formed by rapid growth in cloud size)Tropical storm: 2Because the air above the point of evaporation is rising, there is NO AIR PRESSURE (or as much) pushing down on the water so the SEA LEVEL RISES at low pressure, causing waves which create STORM SURGESTropical storm: 3Trade winds that converge between tropics causes the cumulonimbus cloud to spin at a high speed, "correlus effect"Tropical storm: coastsNear coasts when the water is shallower, there is less water which can get warmer more quickly, so evaporating takes place more rapidly, causing rapid growth in the cumulonibus cloud, allowing it to collect more waterTropical storm: factsTypically 700km diameter, can exceed 13km in height, northern hemisphere: anti clockwise, southern hemisphere: clockwise, fast rising warm air creates an area of very low pressure ("eye" of the storm) which sucks in air, rotating winds cause low pressure close to the equator and absorb the moisture from the oceans, creating hurricanes, tropical cyclones or typhoons