Restless Earth

Restless Earth

1. Composition

   • Crust - 6km / 60km thick
     • "Lithosphere"
     • Oceanic
       • Thin, Dense Basalt, 6km - 8km
     • Continental
       • Thicker, denser Granite: 25km - 80km
   • Aesthenosphere - Part molten
   • Core
     • Outer: Liquid: Iron/Nickel 4000'c - 5000'c
     • Radioactive - decaying elements
     • Inner: Solid, Fe/Ni - 4000'c - 5000'c
   • Mantle : SOLID
   • Convection currents
     • Hotspots: Two sheets pulled apart by opposing currents
     • Lava-lamp!

2. Plate Boundaries

   • Constructive Margins
     • Magma rises and splits continental crust
     • Eurasian Plate separating from N. American Plate
       • Mid-Atlantic Ridge (Iceland, Mariana Trench)
   • Destructive Margnins
     • Oceanic collides with Continental
       • Denser basaltic sinks beneath Continental
       • Subduction
         • Creates deep ocean trench
         • Oceanic plate put under head + pressure
           • Lightweight material rises - Volcanoes form after 100km deep
       • Plate collision causes fold mountains - Andes
   • Conservative Margins
     • Two plates slide past (Diff directions)
     • No volcanoes, no new/destroyed crust
     • Sudden lurches in the fault line
       • EARTHQUAKES
       • San Andreas fault line - USA

3. Hazards + Causes

   • Variables:
     • Size of event
     • Vulnerability of population
       • Poverty
       • Density
     • Population's Capacity to cope
       • Drills
       • Infrastructure precautions
   • Volcanoes
     • Strato (composite) volcano
       • Alternating ash-lava layers
       • Pyroclastic flows
       • E.g. Mt. St. Helens
     • Shield Volcano
       • Gentle slopes, all-lava
       • Fluid, quick basalt-rich lava
       • Frequent gentle eruptions
       • E.g. Mauna Loa (Hawaii)
     • Cone Volcano
       • Tall, steep sided
       • Viscous, silica-rich lava
       • Explosive, unpredictable
       • Violent explosions
   • Earthquakes
     • Variable Factors
       • Magnitude (RIchter Scale)
       • Depth (Shallow=Destructive)
       • Distance from epicentre)
       • Time of Day
       • Preparedness
       • Response efforts!
       • Poorer countries -> Impact on people
       • Developed countries -> Economic cost
     • Primary impacts: Immediate mortality/destruction
     • Secondary impacts: Shelter, supplies, fires
     • Mercalli Scale
       • 1-12 in slowly increasing steps
         • 1: Only detected by instruments
         • 12: No buildings remain standing
           • Gas, electricity, water out
           • Ground shifts + Distorts
       • Measures seismic tremors
   • Tsunamis
     • Caused by earthquakes and volcanoes
     • Groups of waves converge
       • Travel at 900km/h
       • 20-30m high
     • E.g. 2004 Boxing Day Tsunami - Indian Ocean
       • [250,000] dead in 14 countries

4. Living with Disasters

   • Sakurajima Volcano - Japan
     • Benefits
       • Joined itself to nearby land in 1914 eruption
       • 40% Surrounding soil extremely fertile
         • Strong farming industry
       • Strong fishing industry
     • Risks
       • Destructive plate boundary - very dangerous
       • 200 eruptions/year
       • Pyroclastic flows [2 km] long
       • Ash: [30km3] a year
       • Lava bombs thrown [3km] from crater
       • High-density urban areas nearby
         • A large eruption could wipe out nearby city
       • 650,000 people live in hazard zone
     • Prediction:
       • Hot springs are monitored
       • Titlmeters detect volcano swelling
       • Boreholes measure underground water temp'.
       • Seismometers dug into volcano's side measure tremors
     • Protection:
       • Concrete channels divert mudflow
       • Evacuation drills and signposted escape routes
       • Concrete shelters protect against lava bombs
       • Japan is developed, can afford repairs
   • Prediction and Evacuation
     • Gas emission and tremors can be measured
     • Bulging flanks e.g. Mt. St. Helen's
     • 120,000 evacuated from Mt. Pinatubo (Philippines) before it erupted
     • Emergency plans
     • Well trained/funded emergency services
     • Evac. routes, warning systems
     • 'Mitigation'
       • Developed world:
         • Deep foundations
         • Shock Absorbers
         • Cross-Bracing
         • Anti-sway Pendulum
       • Developing World
         • Lightweight roofs
         • Hollow bricks
         • Strengthen weakpoints
         • Planned landuse
   • Mount St. Helens (1980)
     • Composite Volcano
     • Lies on DESTRUCTIVE boundary
     • Cryptodome formed when lava from prev. eruptions and ice blocked the magma chamber
       • Swelled at 6ft per day, global media attention
     • 5.1 magnitude tremor triggered largest landslide ever recorded
       • 1,300 feet of the cryptodome collapsed at 100mph
         • Pressurised magma chamber then exploded [20,000 atomic bombs]
     • Impacts:
       • Social
         • [58] deaths, mainly suffocation
         • [200] houses lost
         • [1000+] flights cancelled
         • Months of manual labour to clean ash
         • Fine ash and grit affected national grid
           • Blackouts nationwide
       • Economic
         • [200] houses destroyed
         • [15mi] railway track lost
         • [185mi] road lost
         • [$2 million] spent clearing up ash from parks, houses
         • Total recovery: $2 Billion
       • Environmental
         • Superheated 600'c ash and lava killed all within [17] miles
         • 60,000 acres of heavily forested land wiped out
           • Weakened timber industry
             • Responded by planting millions of trees on mineral-rich soil
   • Kobe Earthquake, Japan (1995)
     • Began 5:45am, lasted 20 seconds
     • One of the costliest disasters in history
       • $75 Billion worth of damage
     • Japans lies upon 3 subduction zones:
       • Eurasian, Phillipines + Pacific plate
     • Losses:
       • 6,500 dead
       • £7.5 Bil infrastructure damage
       • Electricity, water + gas disabled
       • Fast emergency response, but many areas trapped
       • Highrise landscape devastated
     • Kobe built on RECLAIMED LAND
       • 'Liquification' occured in wet foundations
         • Ground became unstable; Skyscrapers collapsed
     • MEDC
     • Magnitude 7.3
   • Sichuan Earthquake, China (2008)
     • Eurasian and Indian collision zone
     • Magnitude 7.8
     • LEDC
     • Losses:
       • 70,000 dead
       • 5 million homeless
         • Simple wood/mud huts
       • 400,000 injured
       • 80% Buildings collapsed
     • Strong Response:
       • Chinese military provided support
       • Parachutes provided aid
       • Cleanup operations removed bodies
       • Injured occupied hospitals for months
         • Disease spread

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