Natural Hazards An Overview

							Chapter 4 - Natural Hazards:
An Overview
Effects of hazards on humans
   scope: $50 billion/year
   average of 150,000 dead/year
   social loss - employment, anguish,
    productivity
   humans located in the way of natural
    processes
Problems
   hazardous zones: geologically active
   good vs bad - depends on POV
   few if any places are free from all
    hazards
magnitude and frequency
   magnitude: size of event
   frequency: recurrence interval
       % chance per year
   hi magnitude, low frequency usually
    most dangerous
catastrophe potential
   Latin and Greek - overturn or overthrow
       extraordinary or violent change
       any great or sudden calamity, disaster, or
        misfortune
       any event that disturbs or overthrows the order of
        things
   complex response & threshold crossings
       dramatic effect of “small” hazard
   geologic importance is debated by geologists
   table p 106
Evaluation of hazards
   purpose - to minimize loss
   methods: identify susceptible areas
    based on:
       past events - history of area
       studies of process
       physical location
Evaluation of Hazards
   media - human impact
   scientists
       conservative
       reluctant to make statements without disclaimers
           based on
           it is likely
           lack 100% agreement
   communication problems
Evaluation of                         prediction
                                          warning – this will happen
Hazards                                   specific
                                              time
   forecast                                  place
       general location                      magnitude
       magnitude range                   based on
       chance of                             precursors
                                                   ie heavy rain = flood
        occurrence
                                              non or pseudo science -
           not specific                       beware
           ratio = 1:100 or 100                   often wrong
            yr flood                               certain to be correct
           percent - 50% over                      occasionally
            next 15 yrs                   dangers
                                              boy who cried wolf
                                              affects people and businesses
Risk assessment
   probability x consequences
       qualitative - determine factors
       quantitative
           assign # values to risk
           # values may be hard to determine
   Acceptable risk
       based on
           personal control
           public perception
   problems
   opportunities
Impact of and recovery from
disasters
   impact
       direct
       indirect
   recovery - figure p 115
       emergency work
       restoration
       reconstruction I: recovery to pre-disaster
       reconstruction II: may plan to decrease effects of
        repeat disaster
Adjusting to hazards
   reactive - after the fact
   proactive - before the fact
       avoidance
           identification and probability
           predictions and forecasts
           risk assessments
       land use planning
           hazard studies and zoning
           insurance
           evacuation plans
           disaster preparedness
           bear the loss - ride it out
       artificial control
           deflect/redirect the hazard
           stabilize problem areas
Climate change, land use
change, and hazards
   effects floods, erosion, landslides,
    drought, fires
   alters locations and probabilities
   normal, long-term change
Population increase and
natural hazards
   increases demands on land and
    resources
   pushes people into marginal areas
Chapter 5: Earthquakes &
Related Phenomena
EQ features
   epicenter
   hypocenter (focus)
   seismic waves
   fault
   rupture
       below ground
       surface
Magnitude
   amount of shaking
   normalized to set distance
   Richter magnitude
       largest amplitude S-wave
       logarithmic scale
       energy is 30X for each level
   Moment magnitude
       seismic moment based on
           average amount of slip on fault
           area actually ruptured
           strength of rx that failed
       more quantitative and accurate
Intensity
   based on personal observations of
    severity of shaking
   quantifies damage – mag. doesn’t
   Shows variation for different areas
    affected by EQ
   modified Mercalli scale
Faults
   cause
       plate boundary - may be far from actual boundary
       intraplate - weak zones
           former plate boundaries
           Addition or removal of material
   types
       Dip slip
           normal
           reverse & thrust
       Strike slip - right lateral, left lateral
       oblique slip
       buried/blind faults - no surface trace
   zone - related faults may be of several types
EQ causes
   EQ cycle - Elastic rebound theory
       stress builds up
       exceeds strength
       rocks snap back
       vibrations = EQ
       recurrence depends on rock strength
   Human induced EQs
       addition of water
           reservoirs (increases pressure and lubricates fault
           fluid injection
       explosions & nuclear tests
Seismic activity
   Identification
       plot foci
       date movements of soils and other features
       study stress field and measure stain
   tectonic creep - constant movement (small or
    no EQs)
   classification (table p 137
       active fault zone - Holocene (10K yr)
       potentially active - Quaternary (2M yr)
       inactive - no activity for 2M yr
Seismic Waves
   Body waves - hi freq 05 -20hz
       P-wave
           fastest
       S-wave
           thru solid only
   Surface waves - lo freq <1hz
       Love - shear (side to side)
       Rayleigh - oscillation - fig p 139
Seismology
   Measuring seismic waves
       seismograph
       seismic station
       seismogram
   Location by triangulation
       S&P wave arrivals
       Distance radios for 3 stations
    Shaking
   frequency
       building vs EQ wave
       harmonics - natural freq of vibration
           low building - hi freq
           tall buildings - low freq
   materials - natural freqs vary
   distance
       hi freq wave decay most quickly
       tall bldgs are damaged at greater distances
Shaking
   amplification
       material - most intense in unconsolidated
        material!!!
       directivity - most intense in direction of fault
        rupture
   ground acceleration
       acceleration of ground as EQ waves pass
       horizontal & vertical
   distance
       depth of focus
       horizontal distance
Primary Effects of EQs
   ground motion
   Fault rupture - very localized
   Shaking
       collapse buildings
       knock things down
       bend things
Secondary effects of EQs
   liquefaction
       water saturated material
       material acts as a liquid
   landslides
   fires - broken power and gas lines - result loss
    of life
   water bodies
       tsunamis - long wavelength, fast
       seiches
   changes in land elevation
   disease
Estimation of seismic hazard
   Max. magnitude/intensity
   effect at surface
   estimated fault location
EQ forecast
   recurrence interval
   expected magnitudes
   all based on
       fault assessment
       historical record
       earth materials
       stress field measurements
EQ prediction
   Precursors - don’t always occur
       micro earthquake swarms
       preseismic deformation of ground surface
           rates of uplift or subsidence
       radon gas release may increase
       seismic gaps (locked fault
       magnetic fluctuations
       electrical resistivity
           varies with earth materials, groundwater, and others
           changes before EQ
       animal behavior
           not reliable
           could relate to other precursors
EQ hazard reduction
   mapping
       active fault zones
       earth materials sensitive to shaking
   research to predict and control EQs
   develop and improve adjustment
       building design
       land-use planning & hazard assessment
           siting assessment for new facilities
           hazard assessment for existing facilities
       Insurance and relief
   warning systems
       small seismic sensors
       15sec - 1min warning
EQ Hazard perception
   denial
   acceptance
       why?
         education
         experience

       response
         move away
         prepare
Chapter 6: Volcanic Activity
Volcanoes
   Magma rises to surface
   eruption
       lava
       pyroclastics
       gas
   landform: Paricutin
       vent
       cone
       caldera
       rift
volcano types and eruption
manner - table p 176
   factors
       Gas content (hi gas = explosive)
       Si content (hi Si content = explosive)
       hi viscosity = explosive
   types
       Shield - quiet
       Cinder - explosive
       Composite - quiet/explosive
       Volcanic domes - explosive
       Flood basalts - quiet
Origins: plate tectonics
   mid-ocean ridge
   hot spots
   subduction zones
Volcano Effects
   Lava flows
       Aa, slow blocky
       Pahoehoe, fast ropey
Volcano Effects
   Pyroclastic activity
       tephra blown from vent into air
       ash fall
           wide spread
           buries, contaminates H2O, collapses structures,
            respiratory problems, kills vegetation
       ash flow
           supported by gas
           huee ardente
           lateral blast (one type Mt St Helens
           cloud collapse
Volcano Effects
   gases
       types
           water vapor
           CO2
           CO, SO2, H2SO4
       emission
           during eruption
           during dormancy
           1986 Lake Wios, Cameroon
               heavier than air
               dissolved in H2O
               released quickly due to agitation
Volcano Effects
   debris flows and mudflows (lahars)
       ash and water esp. from snow and/or ice
       landslide hazard
       may be large and fast
       may dam rivers or more far downstream
       during eruption and after eruption
   Fires
Volcano Effects
   Caldera - forming eruptions
       vary in size eg Crater Lake 7K yrs ago,
        Yellowstone, 600K yrs ago
       massive release of material
       collapse of overlying material
       dormant result may linger for a long time
       Long Valley, CA
   hot springs & geysers
Identification of volcanic hazard

     activity
         active
         dormant
         inactive
     hazardous areas
         identify effects of previous eruptions
         examine current conditions
prediction of eruptions
   Geophysical monitoring
       seismic monitoring
       magnetic
       thermal
   hydrologic
   topographic changes
   tilting
   gas emissions
       geochemistry
       quantity
   geologic history
Adjustment to and perception
of hazard
   mapping - land use planning
   evacuation
   warning system: table p 201
   diversion of lava flows
       bombing - of lava in a channel - blocks
        channel
       water - chilling creates lava wall
       walls
Chapter 7: Rivers & Flooding
Basics of rivers
   flowing surface water within a channel
   source of water – precipitation via:
       overland flow
       groundwater
Basics of rivers
   basin (watershed)
       area drained by stream
       characteristics
         size
         drainage density

         relief
Basics of rivers
   channel
       shape - width and depth
       gradient
       velocity
       discharge - volume/time
       pattern
         braided - bars
         sinuous/meandering - fig p 217
         pools and riffles
Basics of rivers
   sediment load
       suspended load
       bed load
       dissolved load
   erosion and deposition
Basics of rivers
   dynamic equilibrium
       describes relationship between all of the
        above
       disturbing one disturbs all
       stream will alter until a new balance is
        reached
         land use change - fig p 215
         dam - fig p 216
Flooding
   overbank flow
   causes
       precipitation rate (or snowmelt rate)
        exceeds infiltration capacity, affected by
         soil/rock type
         preceding rainfall

         freezing

       dam failure
floodplain
   plain adjacent to river, subject to
    flooding
   geomorphic definition
       formed by migration of river
       overbank deposition includes natural
        levees
   engineering/legal definition
       area covered by flooding
   stores water –esp. wetlands
types of floods
   upstream
       short intense rainfall
       small area
       dissipate downstream
   downstream ie. 1993 Mississippi flood
       long duration, wide spread storms
       cumulative effect of med-lg flows on many
        streams
       long duration of downstream events is done, in
        part, to flood plain storage (travel time)
       dam failure instant release of stored water
What hazards do floods pose?
   primary effects
       human injury and death
       water damage
       sediment damage
       erosion - note bank erosion
   secondary effects
       hunger
       disease
       displacement
       fires
What effects the amount of
damage caused by a flood?
   land use
   flood magnitude
   rate of rise
   duration - seepage behind levees
   season
   sediment load
   effectiveness of warning
identification of flood prone
areas
   topography
   soils
   wetlands
   vegetation zones
   historical development
   historical floods
Magnitude and Frequency of
Floods
   flow events - hydrograph
   gaging station
   stage & discharge
recurrence interval
   express as ___- year flood or % chance/year
   R = (N+1)/M
       N = number of years of record
       M = rank of flow in array: pick highest flow from
        each year and rank or rank all flows exceeding a
        given stage Plot on log-normal paper
   recurrence interval of largest flood is always
    years of record + 1
Importance of the flood record
   quality of the record
   more record = better analysis
       flood deposits
       vegetation
   climate change
   flood populations
floodplain development
   why develop the floodplain?
       good farming - soils - water
       near transportation
       flat
   flood control
       levees, dams, channelization
       restricts floodwaters, increases stage
       encourages more development
Urbanization & Flooding
   alters rainfall to runoff relationship
       increases drainage density
       decreases permeability and infiltration
        capacity
   results
       increases frequency
       increases flood stages
       flashier floods
     Channelization - fig p 229
   adverse effects
       habitat - consider biology with dynamic equilibrium
       flow
       erosion - incision and/or widening - alters dynamic
        equilibrium
       increases downstream flooding usually
   benefits
       improves navigation
       reduce flooding
       some try to mimic natural systems
       river restoration
       redirection of erosion and deposition
Flood prevention
   fight nature - often results in increase of flood
    magnitude
   methods
       levees
       dams
       channelization
       retention ponds
           mimic lost infiltration
           store water - fig p 228
adjustment to flood hazard
    work w/ nature
   flood proofing
   regulationss based on calculated magnitude
    and frequency
       flood hazard maps
       zoning areas
           floodway - provides passage of 20 or 100 yr flood without
            elevation increase and allows for few if any structures
           floodway fringe - limited development, subject to 100 yr
            flood back water
           relocation of people
special flooding problems
   building in the path of over-land flow
   bank erosion
perception of flooding
   accurate knowledge does not inhibit all
    development
   maps not always effective
    communication
   upstream development is scapegoat
   personal knowledge varies
Chapter 8: Slope Processes,
Landslides, and Subsidence
Mass wasting
   Down slope movement of material
       Dynamic
       material moving
Classification of slope failures
   basis
       material - rock vs soil
       water content - wet vs dry
       rate - slow vs fast
       shape - rotational vs translational
Classification of slope failures
   types
       flows - incoherent
       slides - coherent
       falls
       creep
       subsidence
       snow avalanche
factors effecting slope stability
   Forces on slope
       driving vs resisting
       weight vs shear strength
       load vs support
factors effecting slope stability
   Material Type
   Slope angle
   Climate
   Vegetation
   Water (Very important)
   Addition or removal of slope materials
   Time
What causes slope failure?
   long-term changes (core cause)
   trigger – immediate cause
       vibration (inc. earthquakes)
       rapid moisture increase
       addition or removal of slope materials
slopes and humans
   humans building in the way
   enhanced by humans - humans induce long-
    term changes and triggers
       timber harvesting
       urbanization/development - fig p 256
           septic fields
           loading
           toe removal
   humans create unstable situations
Hazard recognition
   slope stability maps
   landslide inventory
   landslide risk and land-use
   location of property
       base of slope
       top of slope
       mouth of valley - debris fan
What features are evidence of
an unstable slope?
   buildings - cracked, stuck doors
   crooked fences and retaining walls
   broken underground pipes
   uneven pavement
   uneven ground
   cracks in ground
   trees - tilted - buttressed
   rockfalls
   slump features
Preventing slope failure
   Careful planning of human activities AVOID
       sensitive slopes
       loading
       cutting
       wetting
   drainage and dewatering - gutters & french
    drains
   grading and benching
   retaining walls
   bolting, netting, spray crete
Response to unstable slopes
   Warning systems
       surveillance
       tilt meters
       geophones
   Landslide correction
       stopping active slide
       removal of water - drainage
What causes land subsidence?
   withdrawal of fluids - oil or water - p
    263-264
   mining
   Karst
       limestone and dolomite > dissolving rock >
        loss of rock/H2O > surface collapse
Land subsidence effects
   large areas
       zones above mines & wells
   small areas
       sinkholes
       above mine shafts & caves
identification of subsidence-
prone areas
   look for historical evidence
   look for danger signs
       mines
       soluble rock
Chapter 9: Coastal Processes
characteristics of the coast
   transitional zone – land & water
   population concentration
   coast types
       erosional vs “depositional”
       ocean vs Great Lakes
wave generation
   wind
       velocity
       duration
       fetch
   earth movement
   gravity
wave types
   open ocean
       oscillation
       movement is to a depth of ½ wave length
       advance until they hit coasts
   shallow water - fig p 275
       translation
       waves touch bottom
           turn toward coast
           focus on headlands
       break
wave erosion
   water pressure
   abrasion with sediment
   entrainment
   forms - fig p 281
       cliff
       platform
wave transportation
   longshore drift
       sediment moves along the coast
       constant movement
   rip currents - fig p 279
   littoral cell
       source: river, coastal erosion
       moves along beach
       moves off shore
   beach budget - seasonal/annual
beach form - fig p 278
   cliff or dune
   berms (old beach faces) if any
   beach face
   swash zone
   surf zone
   breaker zone (longshore bar
   note zone of littoral transport
Coastal Erosion
   causes
       storms
           storm surge
           waves
       human interference
       sea level rise: worldwide 2-3mm/yr, 1"/10yr,
        1ft/100yr
   effects
       sea cliff erosion
       beach erosion
           seasonal
           long term
storm surge
   local rise in sea level
       wind and low pressure push water onto coast
   added to tide
   waves on top
   moves waves farther on shore: may result in
    “overwash” of barrier islands
   solutions
       build well above sea level
       build barriers
tropical cyclones
   powerful storms
       tropical storms - winds up to 60 mph
       typhoons and hurricanes - winds greater than 60
        mph/100 kph
   damage
       initial damage (coastal
           high winds
           heavy rainfall - flooding
           storm surge - shoreline flooding
       secondary effects (inland
           heavy rains - flooding
           slope failure
Responses to coastal hazards
   bear the loss
   engineering: http://www.env.duke.edu/psds/
       types
           groin & jetties
           seawall, revetment
           break water
           beach nourishment & dune building
       problems
           enhanced erosion
           disruption of littoral drift
adapt behavior
   e-zones - p 297
   principles
       coastal erosion is a natural process
       shoreline construction causes change
       structural stabilization
         high cost
         limited benefit
         eventually destroys beaches
         encourages poor development trends