Hazards???

• Secondary hazards of earthquakes

  - large landslides= esp in mountainous areas
• Primary hazards of earthquakes

  - ground shaking= ranges in duration and severity based on mag of earthquake and distance from epicentre

  - crustal fracturing= visibly sepetare and deep fissures in ground created
• Earthquake waves

  - Secondary waves(S waves)= make ground shake violently

  -> only produced by some earthquakes

  - love waves(L waves)= cause most damage inc crustal fracturing

  -> only travel across surface and large amplitude

  - primary waves(P waves)= when tectonic stress is released

  -> fastest but least damage
• underwater earthquakes

  - move seabed= water displaced~> tsunami?

  - can be shallow=smaller or deep focus=bigger tsunami

  - waves travel fast in deep water= happen w/o warning
• Deep focus earthquakes

  - focus= 70 to 700km under earths surface

  - caused by previously subduct end crust moving towards core either heating up or decomposing

  - less damaging bc shock waves have to travel further= less shaking at surface
• Shallow focus earthquakes

  - focus= 0 to 70 km under earths surface
• Terminology

  - focus= where pressure is released underground and where energy radiates out from= place with strongest waves= most damage

  - epicentre= point directly above centre of earthquake on surface

  - seismic waves= energy released from focus in shock waves

  ->most damage=where shock waves are strongest eg close to epicentre
• Caused by relapse of built up stress

  - plates=always moving= tensions can build up

  - tension can be suddenly released when strain overcomes elasticity of rock

  - release of stress= parts of surface to expand intense shaking motion for a few seconds
• transfer of energy

  - large amounts of energy released

  - transfers vertically to surface and moves outwards from epicentr(point on surface above focus) as seismic waves

  - after fracture rocks may regain original shape but in new position
• Processes at conservative plate margins

  - no volcanic activity

  - earthquake= high magnitude shallow focus (<70km deep) and common

  -> eg San Andreas fault in California
• Process at collision margins

  - meeting of two continental landmasses making a fold mountain belt

  -> collision between indo austrialian and Eurasian plates= Himalayan mountain range

  - no volcanic activity

  - earthquakes= very rare, but when they do happen= high magnitude and low focus(<70km deep)
• Process at convergent margins

  - deep sea trenches and fold mountains

  - volcanic activity= violent bc of high viscosity lava

  - earthquakes= high magnitude and deep focus (up to 700km deep)

  ->eg in western South America
• Process at divergent margins

  - volcanoes= basaltic and parodic low viscosity lava

  - earthquakes= low magnitude and shallow focus(<70km deep)
• slab pull

  -convergent boundaries the high density ocean floor is being dragged down by gravitational force= slab pull beneath continental crust
• Wegener's continental drift hypothesis

  -1912= sepesre continents once joined as a supercontinent
• Gravitational sliding

  Elevated altitudes of oceanic crust at ridges at divergent plate boundaries - create a 'slope' down which oceanic plates slide
• Holmes' hypothesis

  -1930s= earths internal radioactive heat was driving force of convention currents in mantle which could move tectonic plates
• sea-floor spreading

  -1960s= discover magnetic stripes in oceanic crust

  -palaeomagnetic signals from past reversals of earths magnetic field prove that new crust is made at mid ocean ridges via sea floor spreading
• Lithosphere

  -consists of crust and upper mantle->tectonic plates

  80-90km thick

  -changes in thickness depends on if oceanic or not

  Ocean crust= 6-10km

  Continental crust= 30-40km
• Asthenosphere

  -part of the mantle

  -semi molten

  - below lithosphere(which floats on top)
• Mantle

  -semi molten

  - between core and crust
• The core

  -central part of earth

  -inner core= solid

  -outer core= liquid

  Both cores made from iron and nickel

  - source of radioactive heat
• Intraplate earthquakes

  -associated with ancient fault lines re activated by tectonic stresses

  -zones of weakness crested as plates move and stress increases
• Intra plate volcanoes

  -volcanoes can happen at hotspots

  -mantle plumes rise towards surface generating basaltic volcanoes

  -plume doesn't move the tectonic plate moves slowly over the plume

  -continued plate movement=chains Of volcanic islands which become extinct furtherest away from plume
• Causes of INTRA plate earthquakes=hotspots

  -hot mass of rising heat under a weakness in a plate

  -magma rise to surface thro weakness

  -eg Hawaiian islands formed bc of mid pacific hotspot
• Distribution of plate boundaries

  -tectonics hazards happen at SPECIFIC POINTS normally associated with plate margins

  -eg earthquakes can happen where into Australian plate collides with Eurasian plate=collision zone
• Tectonic hazards

  -natural/geophysical event with potential to threaten life n property

  -happen at ALL plate boundaries

  -uneven distribution of hazards some areas are high risk some are low risk
• Continental plates

  - thicker 25-75km

  - less dense

  -granite rock

  - do not subduct
• Oceanic plates

  - make up ocean floor

  - high density

  - made of basaltic rock

  - 7-10km thick

  - subduct under other plates
• Conservative plate margins

  -aka transform

  -plates slide horizontally

  -crust is not destroyed or produced

  -plates snag against each other

  -friction and pressure builds up=plates can't take stress= ground shaking
• Divergent plate margin

  -aka constructive

  -plates move apart

  -convection currents push plates apart= gap

  - magma fills gap

  - new crust generated as plates are pulled away
• Convergent plate margin

  -aka destructive

  -oceanic plate goes subducts under continental= crust destroyed

  -rocks catch against each other bc plates aren't smooth

  -pressure between plates builds up until stress can't be taken= plates split past move= ground shaking
• Secondary hazards of earthquakes

  mountainous areas= large landslides

  • Developing countries struggle to recover bc of lack of infrastructure and resources

  liquefaction= when eq compact loose sediment of silts sand and gravel that are waterlogged

  • compact ground forces water to rise to the surface and damage to buildings and infrastructure= common

  sub marine earthquakes-> tsunamis w/ devastating effects
• primary hazards of volcanoes

  ash falls(tephra)= solid material of varying rain size ejected into atmosphere

  • buildings collapse under weight of ask falling on their roofs
  • air= thick wi/ ash and difficult to breathe= respiratory problems
  • 2010 eruption of mount merapi in Indonesia eg where volcanic ashfall affected surrounding sarea
• PHOV

  volcanic gas= can be poisonous

  • eg carbon dioxide carbon monoxide, hydrogen sulphur and
  • 1986 lake
• PHOV

  pyroclastic flows

  • very hot >800 degrees c
  • high velocity >200km/hour
  • mixture of gases and tephra
  • can destroy everything in its path
  • eg AD70 eruption of Mount Vesuvius, Pompeii italy
  • 1980 eruption of Mount St Helens in usa
• PHOV

  Lava flows

  • usually not major threat if molten bc they are slow moving
  • Create extensive areas of solifided lava
  • land masses created by lava flows= Hawaii and Southwest Iceland
• secondary hazards of volcanoes

  Flooding

  • Jökulhlaup= flooding bc of glaciers or ice caps melting
  • originates from Iceland where subgalcial outburst floods happen at Vatnajökull
• SHOV

  lahars

  • fast mudflows that happen when rain mobilise deposits of volcanic ash
  • 1985 Armero tragedy happened when nevado del Ruiz volcano erupted in colombia
  • 4 Lamar’s came towards town of Armero and 20000ppl died
• Disasters and thresholds

  Disaster= hazard has significant impact on ppl

  -> consequence of hazard happening

  if this damage caused by a hazard exceeds a threshold level = disaster has happened