Tectonic-activity-and-hazards

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Tectonic-activity-and-hazards

  1. 1. 6GEO4 Unit 4 Tectonic Activity and Hazards
  2. 2. What is this option about?• The Tectonic Activity andHazards option focuses on therange of natural hazardsgenerated by plate tectonics• In addition to understandingwhy these hazards happen,you will need to understand:• The impact of tectonicprocesses on the landscape• The impact of tectonic hazardson people• The ways in which peoplerespond to, and try to manage,natural hazards.Primary hazards SecondaryhazardsEarthquakes TsunamiLandslidesLiquefactionVolcanoes LaharsLandslidesTsunami
  3. 3. 1. Tectonic activity and causes2. Tectonic hazards physical impacts3. Tectonic hazards human impacts4. Response to tectonic hazardsCONTENTSClick on the information icon to jump to that section.Click on the home button to return to this contents page
  4. 4. 1. Tectonic activity and causes• Tectonic activity can produce avery large range of hazard events• Not all of these events are‘disasters’• A natural hazard event becomesa disaster when the event causesa significant impact on avulnerable population.• These impacts could be human(death, injury) and / or economic(property losses, loss of income).• Definitions vary, but ‘significant’losses usually means 10+ deaths /100+ affected / $1 million losses.The Dregg disaster model
  5. 5. Event profiles• Not all tectonic hazards are the same• Event profiles are a common way of comparingdifferent hazards• In this example the 2004 Asian Tsunami and ongoingeruption of Kilauea on Hawaii are compared• Hazard profiles can be drawn for any event.
  6. 6. Earth’s heat engine• Tectonic processes aredriven by radioactivedecay in the core• This decay generatesheat inside the earth,which drives vastconvection currents• This convection islargely responsible forplate movement
  7. 7. Tectonic settings and plates• Most tectonic hazards are concentrated at plate margins(boundaries), although ‘hotspots’ are a notable exception.• Different types of boundary generate very different tectonichazards.
  8. 8. The range of volcanic hazards• Dangerous volcanichazards are foundalong subductionzones at destructiveplate margins• The most dangerousvolcanoes arethemselves multiplehazard areas.• Volcanoes atconstructive platemargins (Iceland) andoceanichotspots(Hawaii) aremuch less hazardousand destructive.
  9. 9. Magma generationMagmatypeGeneration Tectonic setting HazardsBasalticLow silica, low gas, lowviscosity.Dry partial melting ofupper mantleOceanic Hot spot (Hawaii)Constructive (Iceland)Lava flowAndesiticIntermediateWet partial melting ofsubducting platesDestructive plate margin(Andes)Island arc margin(Montserrat)Lava flow, ash and tephra,pyroclastic flow, lahar, gasemissionRhyoliticHigh silica, high gas, highviscosity.In situ melting oflower continentalcrust(very rare eruptions)Continental Hot spot(Yellowstone)Continent collision zone(Himalayas)Cataclysmic explosion,pyroclastic flow• Magma, molten rock in the earth’s crust, has an important relationshipwith volcanic explosivity and hazard level• Andesitic magmas, formed by wet partial melting at subduction zonesproduce highly explosive and destructive composite volcanoes
  10. 10. Measuring volcanic explosivity:• The VolcanicExplosivity Index (VEI)is used to measurevolcanic power.• VEI measures: Volumeof ejecta Height of theeruption columnDuration of theeruption.• Modern humans havenever experienced aVEI 7 or 8
  11. 11. Earthquakes• Earthquakes are a verycommon, sudden release ofenergy that generate seismicwaves• Most occur along faults (cracksin the earth’s crust) whichbecome ‘locked’• Opposing tectonic forces pushagainst the locked fault,building up strain, whicheventually gives way releasingstored energy• This energy spreads out rapidlyfrom the earthquake origin (thefocus) reaching the surface atthe epicentre, and thenspreading horizontally.
  12. 12. Tsunami• Tsunami are relatively rare events.• They are generated by submarine earthquakes, volcanic collapse, andcoastal landslides, which suddenly displace huge volumes of water• The 1993 Okushiri tsunami (Japan), 2004 Asian Tsunami and 2009 Samoaevents are all useful as case studies.• Tsunami waves are radically different from normal wind generated oceanwaves.• When a tsunami hits a coastline, the effect is more like a devastatingcoastal flood than a single breaking waves
  13. 13. 2. Tectonic hazards physical impacts• Tectonic processes play a keyrole in forming the landscapearound us• Volcanic activity and themovement of tectonic platescreate mountains, plateauxand other landscape features• These landscapes are thenmodified bygeomorphological processes(weathering, rivers, ice, windand slope processes)
  14. 14. Magma type and volcano morphology• Volcanoes are extrusive igneous landforms. The form of volcanoesis related to magma types, and therefore to different tectonicsettings:• Basaltic – huge, low relief shield volcanoes plus small scoria conesand fissure vents.• Andesitic – steep sided strato-volcanoes; layers of lava, ash andtephra.• Rhyolitic – central craters with lava plugs / domes, due to highviscosity of the lava. Calderas and collapse calderas.
  15. 15. Extrusive igneous activity• Large scale outpourings of basaltic magma, called flood basalts,have occurred at various times in the past.• These produce distinctive lava plateaux and stepped or ‘trap’topography
  16. 16. Intrusive igneous activity• The injection (intrusion) of magma below the surface canproduce characteristic landforms• Igneous rock normally resists weathering and erosion incomparison to surrounding rocks, which produces positive relieffeatures.• Large intrusions such as batholiths produce upland areas,whereas minor intrusions produce smaller landscape features
  17. 17. Earthquakes andfaults• Tectonic movements and movements along faults (whichgenerate earthquakes) also produce distinctive landforms andrelief:Note: diagram not to scale
  18. 18. 3. Tectonic hazards human impacts• A surprising number ofpeople live in areas ofactive tectonic processes• Major tectonic hazards canstrike with devastatingforce• The 2005 KashmirEarthquakes killed around85000, the 2008 Sichuan‘quake over 65,000 and200,000+ died in the 2004Asian Tsunami• It is important to considerwhy people live, in suchlarge numbers, in areas ofgreat risk
  19. 19. Impacts• Every hazard event is different, and therefore the specificimpacts of disaster vary• When researching case studies, it is important to be able toidentify specific impacts and be able to explain these• Some impacts are tangible and can be given a financial value.Others are intangible, such as the destruction of a temple orartwork.• Many losses are direct and immediate such as propertydamage, but others are indirect – these come later and areharder to quantify, such as stress and psychological damage.• Impacts are often considered as human (death, injury,illness), economic (property loss, loss of income, cost ofrelief effort) and physical (changes to landscape andtopography).
  20. 20. • Examine the two earthquakes below and consider how factors such aseconomic development, building types, the geography of the areaaffected and the relief effort may have affected the impacts(South Asian) EarthquakeOctober 2005, Kashmir(Wenchuan) EarthquakeMay 2008, Sichuan, ChinaDetails Magnitude 7.6. Huge number oflandslides accounting for 30%+of deathsMagnitude 8.0. Thrust fault at continentcontinent convergenceFaultdisplacementLargely horizontaldisplacement of up to 10mUp to 5m vertically and 4m horizontally at thesurfaceFocus depth 10 km 19 kmAftershocks 900+ over magnitude 4.0 250+ aftershocks over magnitude 4.0Deaths 80,000 70,000People affected 8 million3-4 million homeless15-30 million5 million homelessInjuries 200,000+ 380,000Damage estimate US$5 billion US$150 billionBuildings Around 1 million damaged/destroyed / severely damagedOver 2 million damaged200,000+ buildings destroyed
  21. 21. Developed versus developing world• It is often said thatdisaster impacts inthe developed worldare largely economic,whereas in thedeveloping world theyare human (death).• You should carefullyconsider if thisgeneralisation is true.(see the table, right)• The 1995 Kobeearthquake in Japanand 1991 eruption ofMt Pinatubo in thePhilippines are usefulexamples to considerDeath Toll Event Location Date5,115 Mount Kelut eruption Indonesia 199123,000 Nevado del Ruiz eruption Colombia 198525,000Spitak Earthquake Armenia 198830,000 Bam earthquake Iran 200335,000 Manjil Rudbar earthquake Iran 199036,000 Krakatoa eruption tsunami Indonesia 188366,000 Ancash earthquake Peru 197069,197 Sichuan earthquake China 200886,000 Kashmir earthquake Pakistan 2005100,000 Tsunami Messina, Italy 1908105,000 Great Kanto earthquake Japan 1923230,000Indian Ocean tsunami Indian Ocean 2004245,000 Tangshan earthquake China 1976
  22. 22. Impacts over time• A simplified version of Park’s hazard response model is shownbelow• Different hazard events have different impacts, shown by thespeed of the drop in quality of life, the duration of the decline,and the speed and nature of recovery.• The differences in the 3 lines might be related to type ofhazard, degree of preparedness, speed of the relief effort andthe nature of recovery and rebuilding.
  23. 23. 4. Response to tectonic hazards• People cope with naturalhazards in very different ways• The chosen ways are oftenrelated to wealth and accessto technology• Humans do have a capacity toignore or seriouslyunderestimate risk, even whenit seems obvious to others• Often it may seem obvious thatpeople should move out ofharms way, but in reality thismay be impossible.
  24. 24. Hazard modification• Several different approaches can be taken to reduce the impacts oftectonic hazards:Modify theevent(hazardmitigation)Modify humanvulnerabilityModify thelossTsunami Coastal defencesand engineering•Warming and prediction systems•Coastal zone management andlanduse planning•Provision of emergency kitsLoss modificationinvolves immediaterescue efforts,followed by reliefefforts which focuson food, shelter,water andsanitation.Insurance can helprecovery.Long termreconstruction isneeded.Earthquakes Not possible •Ground shaking and liquefactionrisk mapping•Aseismic buildings•Earthquake education and drills•Prediction not possibleVolcanoes Lava diversion •Monitoring, prediction warningand evacuation systems•Hazard mapping e.g. lahar risk•Education•Shelters
  25. 25. The hazard management cycle• Successful hazardmanagement involves a cycle(see diagram) which focuseson the 3 types of modificationfrom the previous slide.• A focus on modifying loss only,will not improve survivalchances when the next hazardstrikes• Long before a natural hazardevent, there needs to be afocus on mitigation andprevention (if possible) as wellas human preparedness.

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