312 2024 notes
Module 1 + 2: Catastrophe
Natural hazard: Geophysical processes that can impact human life and property
Risk: Vulnerability, mechanisms for hazards
Hazard: Probability that a specific hazardous event will happen in a given time frame
Vulnerability: Susceptibility to a given hazard based on exposure (uneven)
Humans have a role in their vulnerability to hazards by making choices of lifestyle and spaces they inhabit
Risk equation: Risk = (Hazard * Vulnerability) / Capacity
Natural hazards approach: action now to reduce vulnerability later 1.Assess, 2.Mitigate, 3.Prepare, 4.Respond, 5.Recover
Module 3 + 4: Earthquakes
E.g.: Denali earthquake, Nov 2002.
Elastic rebound model: Shear stress released at faults cause rocks to spring back as they let go
Hypocentre/focus: point location where fault rupture initiates within crust
Epicentre: spot above hypocentre on surface
Body waves (3D): P-wave (compression, good energy transfer), S-wave (shear, slower, no liquids)
Surface waves (2D): Love wave (surface side to side), Rayleigh wave (surface rolling)
Seismic wave order: P-waves, S-waves, surface waves (largest amplitude)
Intensity vs magnitude: shaking felt at a specific point (varies) vs energy at fault rupture
Qualitative scale: Modified Mercalli Index Quantitative scale: Richter scale
Seismic moment: How much force needed to generate waves (M0): M0 = µ*D*A
Moment magnitude: Measures earthquake magnitude using its seismic moment: Mw=2/3logM0-10.7
M9 megathrust (300-400 years sub zone), M6-7 deep (20-30 year rock slips), M3-7 shallow crustal (short)
Mitigation: Improving building design to withstand shear forces, educating safety through practice drills
Module 5: Tsunamis
E.g.: Tsunami in Palu, Indonesia, 2018. Death toll 1700 people, unexpected event after earthquake at a strike slip fault
Tsunami vs wind blown waves: Long WL and wave run up vs shorter WL and short wave run up in shore
Wave train: Waves travelling in groups, second or third waves may be the largest
Peak ground acceleration: How fast Earth’s surface goes from zero to max velocity as shaking begins
Triggers: Earthquakes (plate subsidence after snap = uplift), landslides (subaerial, submarine), eruptions
Risk distribution: Proximity to triggers, geography of location, proximity to escape routes/safety zones
Mitigation: Passive (warnings, education on signs and action), active (tsunami barricades and structures)
Module 6: Volcanoes
E.g.: Mt Pelée in Martinique.
Decompression melting: Mantle melting due to lowering pressure as magma rises to the plate separation area
Flux melting: Water that hydrated oceanic crust gets released + rises when sub. plate squeezes as it descends
Divergent zones: basalt (makes up oceanic crust) Convergent zones: granitic magma (plutons)
Felsic magma: higher Si and viscosity eruptions (caldera) while mafic magma: lower Si and lower viscosity (shield)
Volcanic Explosivity Index: Measures volcanic eruptions’ explosivity, type, plume height, frequency, tephra amt
Primary hazards of volcano: Forces that directly injure/kill people, property, habitats
Pyroclastic flows: Avalanches of volcanic rocks, ash, gases and can rapidly spread (deadliest volcanic hazard)
Lahar: Fast moving flows of volcanic debris and water, up to 50 km/h
Secondary hazards: Eruption induced environmental changes that lead to famine, distress, etc.
Mitigation: monitoring baseline conditions, measuring seismicity/temps creating reference model of behaviour
Module 7 + 8: Slope failures
E.g.: Garibaldi Barrier, formed due to lava flow meeting glacier and cooling as vertical rock wall, in area of significant topographical relief that experiences change in winder (freezing, warming, change in water), rock structure predisposed to failure
Slope failures characterised by material type (rock, unconsolidated material) and movement type (fall, slide, flow)
Causes: Climate, external forces, slope angle, slow move toward failure over time
Factor of safety: Quantifies and compares variables contributing to failure, allows us to judge needed means of mitigation
Forces acting on a slope: Driving forces (gravity), resisting forces (strength of slope materials), shear (resisting surface slip)
Cause: Prepares slope to fail (can be multiple) Trigger: Last push beyond threshold to fail (single)
Voluntary vs involuntary risk: Placing oneself at high risk as a choice vs not choosing to be at risk
Mitigation: prevent slope failures from occurring, reduce driving, increase resisting, limit development, contain before impact
Module 9: Avalanches
E.g.: Wellington, Washington, 1910. One of the worst in PNW for av. fatalities. Train trapped in snow storm, 96 passengers killed.
20-40 year old males and recreational users have higher exposure to avalanche risk
Highest proportion of avalanche fatalities are due to asphyxiation and not physical trauma
Critical burial: Head is buried beneath snow level/breathing obstructed (52% fatality rate)
Non-critical burial: Airway not obstructed/head above snow level (4% fatality rate)
Powder-type: Single triggering point (-release), form in loose snow, expands in V downhill (small local events)
Slab-type: Triggered from detachment crown, moves as a slab Avalanche safety: Shovel, av. probe, av. transceiver
Wet vs dry: Slow with no cloud, difficult to manually trigger vs fast with cloud of dust, usually triggered by people (stress)
Triggers: Snow accumulation, increased pressure, surface heating, gravitational creep, shaking (most happen after storms)
Preconditions: Slope angle (38˚-45˚ highest risk), loading (wind loading, cornice, cross loading), aspect (direction slope faces, N/NE most at risk due to buildup as it is more cold), hoar formation (crystals rapidly formed through change of water state, can’t support shear stress)
Avalanche problems: Storm slab, wind slab, persistent slab, deep persistent slab, wet slab av., loose dry av., loose wet av., cornices
Mitigation: Identifying avalanche problems and staying away from prone slopes, forecasting avalanche weather (publishing weather info, snowpack info, danger rating), testing for snow stability (extended column compression test [isolating section of snow, tapping with wrist, elbow, shoulder to grade stability], Rutschblock test [jumping on block], artificial triggering [explosives])
Module 10 + 11: Tropical cyclones & flooding
E.g.: Hurricane Matthew, 2016. Cat 5 hurricane devastated Florida, Georgia, Carolina coastlines.
Cyclones (hurricanes, typhoons): intense low pressure systems affected by Coriolis (deflect right in NH and move CCW), tropical cyclones form over tropical ocean waters and derive energy from warm water and evaporation/condensation process
Low pressure system to cyclone: Requires time, storm organisation, and continuous supply of energy
Tropical cyclone formation: Tr. disturbance (wind <63 km/h, 200-600 km dia.), tr. depression (more rotation around pressure centre), tr. storm (wind >63 km/h, high rainfall), hurricane (wind >119 km/h, strong low pressure centre)
Hurricane formation conditions: warm ocean water, large atm temp gradient, little vertical wind shear (allows storm organisation)
Saffir-Simpson scale: Hurricane intensity based on its wind speed
Steering winds: Low or high pressure systems that influence where storm will be pushed as it moves toward land
*Hurricane path pattern: Turn right and north once at Caribbean Sea and Gulf of Mexico due to steering winds
Risk: Intensity of hazard, level of population exposure, poverty, and governance Mitigation: Effective warning messages
Hazards: Wind (hurricane winds can be the strongest on earth, can create projectiles), storm surge (strong winds driving water close to shore and riding tidal level, can cause flooding, highest cause of death in Atlantic hurricanes because poorly understood by public), rainfall, rainfall-induced flooding
Annual flood: Greatest discharge event on stream for that year, used in stats analysis of expected frequency
1 in 100 year flood event is based on long term average of flood occurrence and are randomly distributed, each year has the same chance
Climate change on storm: Overall number decreased (global weakening of tropical circulation in summer) but intensity increased (warmer temperatures allows greater capacity to hold water vapour), also move slower (meaning more precipitation over same area for longer)
Mitigation: Dykes and levée systems, government response to provide assistance in rebuilding and providing new homes
Module 12: Wildland fires
E.g.: Okanagan, Kelowna, 2003. 13 000 hectares in 4 days, 33 000 people displaced.
Main components: Fuel, oxygen, heat
Pre-ignition process: Preheating (excess moisture evaporated through dehydration), pyrolysis (production of volatile gases)
Combustion phases: Pre-ignition, combustion (ignition of pre-ig material, drawing new oxygen to fire, flaming and smouldering combustion), extinction (fire has insufficient heat to sustain itself)
Speed and energy of a fire: Fuel, wind, slope
Pre-ignition rates: Surface material dries out faster than standing material, meaning smaller fuels burn more vigorously
Wind: Supplies oxygen to combustion Slope: Fire moving upslope enhances pre-ignition and intensifies fire
Secondary hazards: Hydrophobic soil layer, lack of vegetation, reduced air quality
Mitigation: Addressing warming and drier climate trends, different approaches to managing fuel, increasing population by creating model that focuses on adaptation to current conditions
Decision window: Time prior to the eruption where people learn about the situation, prepare accordingly, and find escape routes and shelter. More preparation time reduces number of fatalities, difficulties, and critical situations people can find themselves in after.
Access model: analyses the ability of people to deal with impact of hazards they may face (regarding access to resources after hazard)
Return period: n+1/rank Recurrence interval: 1/P