Please enable JavaScript.
Coggle requires JavaScript to display documents.
Geophysical Hazards, Risk Management: identify, assess, prioritise risks
…
Geophysical Hazards
-
-
Volcano
- At convergent, divergent, hotspots
- Mantle plume: long columns of hot rock from deep inside the earth's mantle = channel heat to surface = Hotspots
- Hotspots erupt periodically
-
On ocean floor
- Diverge beneath plates = overlying plate moves wrt plume = successive eruptions in linear series
- Youngest volcano above plume
Continental
- Plume reaches lithosphere = spread laterally + radial flow = uplifting/depression
- Cosgrove Volcanic Chain
Parts
-
-
-
Magma Chamber: reservoir of molten rock located beneath the earth's crust, fed by mantle
-
Lava Viscosity: stickiness, resistance to flow
Basaltic
- Runny
- Low-silica
- Longer to cool
- Retains gas = mobile
- Frequent gentle eruptions
- Hotter
- Sloping volcanoes
Acidic
- Viscous
- High-silica
- Cools quickly
- Loses gases quickly
- Violent eruptions
- Steep-sided volcano
- Less hot
Types of Volcanoes
Composite/Stratovolcano: steeper, larger than cinder-cones
- Acidic lava: more explosive, viscous
- Forms large ash clouds, pyroclastic flows
- Convergent boundaries
- Most common
- Successive eruptions of lava and pyroclastic material --> subsequent eruption covers soft ash, preventing erosion
- Mount St Helens: OP-CP of Juan de Fuca + N. America
- Mount Pinatubo: pacific ring of fire
Cinder Cone Volcano: steep, usually has crater
- Basaltic lava
- Rarely more than 1200m
- Form quickly from successive explosive eruptions
- Mix of gases + magma rises to the surface = violent upward explosion that blasts lava + tiny fragments = solidify = ash + cinders which fall back to the ground
- Cinders: gas-filled chunks of lava that cool rapidly as they sail through air --> accumulate in the cone
Shield Volcano: gently sloping sides + broad summit
- Basaltic lava: less explosive/viscous, flows easily + spreads over a large area
- Forms new sea floor, ocean ridges
- Divergent boundaries, hotspots
- Mauna Loa, Hawaii: Hotspot, pacific plate --> lava spills out of fissure in earth's crust
- Surtsey, Iceland: N. American, Eurasian = sea floor spreading
Volcanic Features
Caldera: collapse of the top of the volcano = large circular depression
- Crater lakes
- Violent eruption blasts off the top/sinks into magma chamber after major eruption
Lava Plateau: regional expanse of thick lava flow
- Lava flows out from narrow openings in the crust, solidifies and builds up layer upon layer
Hot Spring: a pool of hot water that has seeped to the earth's surface to form a small pond
- Fed by water in contact with hot rocks far below the surface
Geyser: special type of hot spring that ejects a column of hot water and steam to great heights at intervals
Volcanic Plug: mass of lava that solidified in the pipe of a volcano
- Volcano becomes extinct and erodes, leaving behind the pipe of solidified lava
Secondary Hazards
Pyroclastic Flows: fast moving mixture of hot blocks of lava pumice, ash, gases that have been exuded from volcanoes
- Stratovolcanoes
- Heavier fragments roll along ground (solid), smaller fragments float in a stream of hot gases
Tephra: flow or rocks, ash, gas
- 70-700km/h --> faster than Lahars
- 200-800 --> hotter than Lahars
- Burns, knocks over, shatters, buries
Lahars: liquid debris flow from pyroclastic material, rocks, water
- Eruption at cold areas + rivers = snow, ice melts = combines with materials, moves downhill
- Up to 200km/h = slower than pyroclastic flows
- 100 max temp = cooler
Landslides: large masses of rock and soil separate from the side of the mountain and slip downhill due to gravity
- Volcanic areas = steep, rocks weakened by leakage of gases beneath the ground
- Speed of 160-250km/h
Triggers
- Earth tremors: magma intruding upwards into neck of volcano
- Explosive eruption
- Earthquake
- Heavy, sustained rainfall: lubricates rocks, saturates the ground
Lava Flows: molten rock pours or oozes from erupting volcano, cools and solidifies
- Composite cone volcanoes: viscous lava flows slowly = not as dangerous
- Shield: less viscous = flows more quickly
Earthquake: vibration of the earth's surface caused by the sudden release of energy stored in the rocks of the earth's crust
- Plate movement = build up of stress on rocks on either side of the fault = cannot withstand increasing stress = slip and release
Parts
Focus: point where seismic waves are released
- Shallow: 0-70km
- Intermediate: 70-300km
- Deep: 300-700km
-
Magnitude: number that characterises the relative size of an earthquake
- Measurement of maximum motion recorded by
Seismic Waves
Body Waves: travel through the interior of the earth
- Arrive before surface waves are emitted
- Higher frequency than surface waves
P waves: fastest seismic wave
- Arrives at seismic station first
- Moves through solid rock and fluids
- Compressional waves: push and pull = particles move in the same direction as the wave
S Waves: arrives after P
- Moves through solid rocks
- Particles move up and down, side-side = perpendicular to wave propagation
Surface Waves: travels through crust only
- Lower frequency than body waves
- Easily distinguished on seismogram
- Almost entirely for damage + destruction
Love Waves: fastest surface wave
- Moves ground side-to-side
- Confined to surface = entirely horizontal motion
Rayleigh Waves: rolls along the ground
- Moves ground up-down, side-side = with wave direction
- Causes most of shaking felt
Causes
Physical
Tectonic Plates
- Compressional/tensional stress built up @ boundaries
Intense temperature
- Change in volume density of rocks and pressure in earth's interior = sudden slipping of rock fragments
Volcanic Activity
- Less severe, limited in extent than those caused by fracturing
Human
Deep Mining
- Leaves caverns at the surface + deep in the earth = stress
- Increased instability = chambers collapse
Crandall Canyon Mine, Utah, USA (2007):
- Pillars ruptured = major collapse over an area of 200,000 sqm
- Magnitude 3.9
- 6 men trapped
- 2nd collapse 4 weeks later killed 3 workers
Underground Nuclear Testing
- Pressure propagates through the ground = generates P waves
North Korea 6th Nuclear Test (2017)
- 250 kilotons explosion = magnitude 6.3
- Area above collapsed in underground cavity --> bomb exploded = 2nd magnitude 4
- Collapse of civilian buildings
- Damage to structures in nearby villages
- 12 killed, 150 injured, affected farmers
Reservoir Induced Seismicity: dams usually in areas under tectonic stress
- Change in stress due to the weight of water
- Increased groundwater pore pressure = decreased strength of rocks below to support
Zipingpu, China (2008)
- 320M tonnes of water over a well-known fault = magnitude 7.9
- 80,000 died/missing
Extraction of Fossil Fuels: fracking = faults slip
- Weight of fluid presses against fault
- Fluid lubricates/cracks faults
Sichuan, China (2019)
- Magnitude 4.9, 1km focus
- Killed 2, injured 12
Groundwater Extraction
- Reduced gravitational load on a fault = less force on rocks on sides of fault that keep it locked = collapse
Dead Sea Transform Fault (2018)
- Extraction = 50m decrease in groundwater level
- Magnitude 4.5
Artifical Induction
- Fluid pressures lubricate faults, counteracting frictional forces on faults
Oklahoma, USA (2011)
- Magnitude 5.6
- Destroyed 14 homes, injured 2
Secondary Hazards
Tsunami
- Large volume of water displaced = giant sea wave
- Large scale flooding, damage
- Only detected by sensitive measurements of changes in deep water pressure
- Reach shallow waters in coastal areas = wave height rises
- 700-1000km/h
Tohoku Tsunami (2011)
Landslides
- Ground vibrations = destabilise cliffs, steep slopes
- Worsened by heavy rain, melting snow, unconsolidated rock
El Salvador (2011)
- Caused a landslide in Santa Tecla
- Killed hundreds
Liquefaction: saturated soil loses strength and rigidity due to applied stress = behaves like water temporarily
- Vibrations/water pressure in a mass of soil = soil particles lose contact with each other
- Unable to support weight + flow down slopes
- EQ vibrates water-saturated/unconsolidated fill (loose, granular sediment/saturated by groundwater/strong shaking)
Palu, Indonesia (2018)
- 7.5 magnitude
- Building collapse
Impacts
Disruption of Services: pipes, electrical cables damaged
Kobe (2004): disruption to 1.2M residents
Fire: overturned stoves, ruptured gas pipes, damage to electrical cables
Kobe (1995)
- Toppled gas cookers, kerosene stoves = hundreds of fires ignited
- Ruptured water pipes = cannot put out
- 7000 buildings destroyed, 500 dead
Destruction of Properties + Infrastructure
Tohoku (2011): hundreds of thousands homeless = housing shortage = $300B USD to repair
Kobe (1995): Hanshin Expressway collapsed, port facilities damaged
- Emergency vehicles, food, medical supplies could not reach
Loss of Lives: due to collapse of buildings, fires, floods, landslides
- High: high magnitude, shallow focus, high population density
- Low: prepared communities, earthquake resistant infrastructure
-
Mass Movement: downslope motion of rock, regolith, snow, ice under the influence of gravity
- Weathered material accumulates on upper slope faster than it erodes = equilibrium disturbed
- Type of material
- Rate of motion
Mechanism of motion:
- Fall: drops vertically
- Slide: Moves as mass along sloping surface, without internal movement
- Flow: has internal motion (required liquid)
Types
Topple
- Forward rotation, movement of mass of rock debris out of slope
- Quick rate, comparable to falls
Creep
- Slow movement down a slope
- Very Slow: soil, overburden, ice mix and flow down
Slumping
- Block of material moves down slowly along a concave surface
- Slow (mm/cm per year)
- When slope is undercut, no support for overlying materials, too much weight on unstable slope
Mudflow
- Mass of loose, water-laden, poorly sorted debris of fragmented rock, soil and mud that surges down a slope in response to gravity
- Loose sediment (clay, silt) and water mix
- Relatively fast (cm/m per s)
Falls
- Rock dislodged by weather, surrounding soil eroded
- Unexpected release of rock/course material from steep slope
- More than 10m/s
Causes
-
Rainfall
- Adds weight
- Lubricates soil
Coastal Erosion:
- Waves collide with cliffs = wearing + cliff retreat = weight of overhang overcomes the strength of rock
Deforestation
- Less roots to stabilise soil
-
-
Risk Management: identify, assess, prioritise risks
- R = HPV
- Risk: probability of a hazard event causing harmful consequences
- Hazard: frequency and expected strength of hazard
- Population size: of exposed area
- Vulnerability: susceptibility of a community to a hazard event/secondary impacts
Measures of Intensity
Earthquake
- Higher magnitudes are less frequent as more time is required to accumulate sufficient stored energy
Richter Scale: each increase is 33x more severe than the previous level
- Minor: 3-3.9
- Light: 4-4.9
- Moderate: 5-5.9
- Strong: 6-6.9
- Major: 7-7.9
- Great: 8
Mercalli Scale
- (not felt) I, II, III, IV, V, VI, VII, VIII, IX, X (extreme)
Volcanoes
Volcanic Explosivity Index: logarithmic scale of 1-8 that quantifies the volume of tephra (rock fragments + particles emitted during an eruption)
- 1 point = 10-fold increase in volume of tephra
Hawaiian (0-1)
- Shield
- Lava pours out gently
- Erupts frequently
Strombolian (1-2) after Stomboli in Italy
- Mildly explosive (tephra up to 1km high)
Vulcanian after Vulcano in Italy
- Dense ash clouds up to 20km high
- Pyroclastic flow
- Rocks, volcanic bombs
Plinian/Vesuvian (3-6)
- High columns of ash/gas more than 25km into stratosphere
- Magma chamber depleted
- Caldera
Ultra-Plinian (>6) (supervolcanoes)
- Ash clouds 45km in stratosphere
- Change average global temperatures up to -0.5 for years
- Yellowstone, Wyoming/ Long Valley, California/ Toba, Indonesia/Taupo, New Zealand
Predicting
-
Volcanoes
Increased frequency, intensity of earthquakes
- Magma pushes upward into magma chamber = pressure on neighbouring rocks = tremors
Swelling of ground surface
- Magma and gas push upwards = slope swells
- Tiltmeters measure angle of slope of a volcano
Fumarolic gases from volcano
- Measure ratios of SO2, CO2, HCl, H2O
- Correlation Spectrometer
- Satellites
Remote Monitoring
- Satellites look for high temperature spots where volcano surfaces are changing
Underestimation
- Psychological denial of risk: deny risk due to benefits of living there
- Hazard occurs infrequently/lack long-term data = cannot assess accurately
- Complacency as hazard occurs frequently
- Little media attention/communication = misinformed
- Underestimated impact of secondary hazards (Tohoku tsunami, water-borne diseases after Haiti earthquake)
Allow for adjustments to be made using COST BENEFIT ANALYSIS:
- Stop hazard
- Modify impacts
- Spread the cost of potential losses
- Plan for losses
- Endure losses
E.g Govt surrounding Indian Ocean: decided that risk posed by a potential tsunami was not great enough to spend millions building an early warning system
200,000 people died in the Boxing Day 2004 Tsunami
-
Hazard Vulnerability Formula
Disaster = (H x V)/C
-Hazard
- Vulnerability: how at risk populations are to natural or human hazards
- Capacity: how able the country/region is to react and recover from a natural hazard
-
-
Adaptation to Hazards
Government Planning (Hazard mapping/land-use zoning)
- Buffer zone: building not permitted
- Defences: flood barriers, levees, lava diversion channels
- Shelters: against flood, avalanche, nuclear
- Evacuation
- Rebuild to new building standards
Eg California: cannot build across fault line, areas at risk of liquefaction
Eg Japan: prohibits construction on low-lying land vulnerable to tsunami
- Disadvantage: UK Flood Risk Map: lowers property value, increases cost of insurance
Personal Resilience
- Insurance: rebuild, receive money for lost income
- Premiums for older/at risk
Eg New Zealand: National Insurance Policy protecting houses against earthquake damageDisadvantages
- Not all can afford (esp LEDCs that need it most)
- Not offered everywhere
- Private companies may deny if risk is too high
- May be less willing to pay to prepare houses since insurance will repair
Home Preparedness
- Seismic retrofitting: modify structures to be resistant to earthquake movement
- Secure pictures/mirrors/furniture to wall
- Shatterproof windows
- Install a safe room (hurricanes + tornadoes)
Emergency Drills: practice steps to take when a hazard occurs
- Move to safe location
- Listen to instructions by trained personnel
- Practice first aid
- Awareness = less panic, irrational behaviour during event
Eg Japan Disaster Prevention Day (1 Sept): practice earthquake drills
Stockpiling: of essential supplies
- Water: pipes may rupture, contaminate supply
- Non-perishable food: production, processing, supply disrupted
- Tents/blankets: homes destroyed = exposed to cold/hot/wet
Pre-event Management
Building Design, Regulations
Damping devices: large weights at the top of tall buildings (water tank/metal ball)
- Swing in opposite direction to building (wind/earthquake)
- Eg Taipei 101
Steel/reinforced concrete
- Withstand earthquake better
- Eg Kobe EQ 1995: parts of highway that did not collapse = reinforced
Wide, heavy based buildings
- More stable foundation
- Eg: TransAmerica Pyramid, San Francisco
Buildings with steep sloping roofs
- Prevent volcanic ash from accumulating
Slope Stabilisation Measures: reduce the likelihood of mass movement events
- Revegetations
- Slope drainage
- Netting, snow fences
- Excavation, infilling of slopes
-
Post-event Management
Risk Perception
Decreased
- Voluntary Hazard
- Few fatalities: UK floods
- Familiar, understood
- Lack awareness
- Small scale, slow impact, low magnitude (flood, drought)
Increased
- Involuntary Hazard = no control = increased fear (earthquake)
- Many fatalities (Indian Ocean Tsunami 2004)
- Unfamiliar/not understood
- Awareness --> media repeatedly warns
- Large scale, fast impact, high magnitude (tsunami)
Responses
Short-term Rescue: days and weeks after
- Search and rescue
- Medical care
- Emergency food aid
Mid-term Rehabilitation: weeks and months after
- Provision of food, water, medicine
- Reopen transport links
- Fix water, electricity supply
- Establish longer-term refugee camps
Long-term Reconstruction: months and years after
- Rebuild destroyed infrastructure
- Kickstart local economy
Case Studies
Earthquake
Haiti, 12 January 2010
- Magnitude 7, 52 aftershocks
- Conservative: Carribean, N. American --> slippage
- Less developed (GDP, access to services, literacy, healthcare)
Impacts
- 200,000 killed, 300,000 injured, 1.3M displaced
- 70% buildings destroyed
- Broken electricity cables = fires
- Landslides blocked off rural areas
- Triggered flooding in coastal areas
- $7.8M in damages
- Agricultural industry destroyed = unemployment
- Damaged transport, communication infrastructure = cut international trade = expensive food prices
Responses: Habitat for Humanity (NGO): 5 year disaster recovery programme for over 250,000
- 24,600 emergency shelter kits
- Built 300 homes, repaired 683
- Constructed 5,000 shelters
- Created 2,100 jobs
- Implemented critical infrastructure --> 2,000 with clean water
- Trained 6,600 in construction, financial literacy, business development, health and hygiene = curb spread of cholera
Effectiveness
- Slow response
- New homes built to a higher standard
Vulnerability: High
- Poorest country in Western Hemisphere
- Vulnerable to natural disasters
- Deforestation = landslides
- Successive disasters take a toll on the Haitian economy = hinders sustainable development
Christchurch, 2010/2011
- Magnitude 7.1, aftershocks
- Convergence: Australian, Pacific --> movement along unknown Greendale (strike-slip) fault --> aftershock from oblique thrust faulting along another undiscovered fault
- More developed (GDP, access to services, literacy, healthcare)
Impact
- $25B for repairs, rebuilding
- 20% migrated from city
- Liquefaction
- Broken pipes = water, sewage flooded the streets
- Thousands of homes damaged
- More than 4500 vehicles stranded
- Schools closed, airport open only for emergencies
- 2010: no loss of life: sleeping at home
- 2011: 185 killed, thousands injured
Responses
- Declared a national state of emergency (2011)
- Cordoned off CBD
- Power companies restored 75% of electricity in 3 days
- Pop-up hospitals set up
- International aid ($6-7M)
- Construction of 10,000 homes + temporary housing
- Canterbury Earthquake Recovery Authority created to organise rebuilding
Effectiveness
- Hampered due to aftershocks
- People discontent with CERA = disbanded in 2016
Vulnerability
- Still many unknown faults
- Highest population in South New Zealand --> 50% deaths caused by building collapse
- Building regulations = reduced vulnerability
Volcano
Anak Krakatau, Indonesia (2018)
- Stratovolcano
- Convergence: Eurasion, Indo-Australian subducted
- Less developed
Impacts
- More than 882 houses, 73 hotels, 434 ships damaged
- Electrical disruption
- Tsunami caused by volcano collapse (killed 437, injured 32,000, displaced 6,000)
Responses
Red Cross Actions International Red Cross
- Mobilised 2.6M HKD to assist 7,000 people in one month
Indonesia Red Cross Society: deployed emergency response teams
- Distributed 5,000L clean water, 484 kitchen set, 350 blankets
- First aid, medical services (24 ambulances, 1 team of orthopaedic specialist doctors, 5 mobile clinics)
- 2 helicopters for search and rescue
Effectiveness
- Lacked funds, mostly international relief
- No long-term, sustainable systems to decrease vulnerability
Vulnerability: High
- Low proximity to coastline
- Early warning systems use ocean buoys = cannot detect tsunamis by landslides
- No buffer zone
- Volcano in active phase = likely to recur
- Along pacific ring of fire = 130 active volcanoes
Eyjafjallajökull, Iceland (2010)
- Stratovolcano
- Divergence: N. American, Eurasian (Mid-Atlantic Boundary)
- Unusual seismic activity, magma entering its magma chamber = pressure
- Interaction of magma and water = plume of fine volcanic ash + gas over 10km high, carried by wind
- More developed
Impact
- 0 fatalities, but irritation symptoms
- Ash covered N. Europe = 20 countries closed airspace (10M travellers affected, $1.7B lost)
- 500 families evacuated
- Ash became wet, compact = difficult to farm, harvest, graze
- Eruption melted glacier = flooding = 700 evacuated
- Ash contaminated water --> fluoride in water = deadly to sheep
Response
- Declared a state of emergency
- Closed the European airspace
- National Centre for Atmospheric Science mapped the volcanic plume to reopen air space
- Warnings issued
- Rescue teams, treatment, food, drink, shelter
- European Red Cross Societies
Vulnerability: Low
- Nordic Volcanological Centre: GPS, seismic monitoring and satellite radar interferometry = early detection and warnings
- Automated phone alert system to inform locals of evacuation plans
- Catastrophe insurance
- Full-scale evacuation exercise practiced in 2006
- But highly populated around the volcano
Effectiveness
- More funds = used technology to predict future eruptions + long-term responses
- Researchers watch volcanoes, monitor gases