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Chapter 4 - Natural Hazards: An Overview
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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
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Problems hazardous zones: geologically active
good vs bad - depends on POV few if any places are free from all hazards
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magnitude and frequency
magnitude: size of event frequency: recurrence interval % chance per year hi magnitude, low frequency usually most dangerous
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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
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Evaluation of hazards purpose - to minimize loss
methods: identify susceptible areas based on: past events - history of area studies of process physical location
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Evaluation of Hazards media - human impact scientists
conservative reluctant to make statements without disclaimers based on it is likely lack 100% agreement communication problems
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Evaluation of Hazards prediction forecast warning – this will happen
specific time place magnitude based on precursors ie heavy rain = flood non or pseudo science - beware often wrong certain to be correct occasionally dangers boy who cried wolf affects people and businesses Evaluation of Hazards forecast general location magnitude range chance of occurrence not specific ratio = 1:100 or 100 yr flood percent - 50% over next 15 yrs
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Risk assessment probability x consequences Acceptable risk problems
qualitative - determine factors quantitative assign # values to risk # values may be hard to determine Acceptable risk based on personal control public perception problems opportunities
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Impact of and recovery from disasters
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
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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
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Climate change, land use change, and hazards
effects floods, erosion, landslides, drought, fires alters locations and probabilities normal, long-term change
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Population increase and natural hazards
increases demands on land and resources pushes people into marginal areas
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Chapter 5: Earthquakes & Related Phenomena
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EQ features epicenter hypocenter (focus) seismic waves fault rupture
below ground surface
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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
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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
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Faults cause types zone - related faults may be of several types
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
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EQ causes EQ cycle - Elastic rebound theory Human induced EQs
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
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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
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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
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Seismology Measuring seismic waves Location by triangulation
seismograph seismic station seismogram Location by triangulation S&P wave arrivals Distance radios for 3 stations
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Shaking frequency materials - natural freqs vary distance
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
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Shaking amplification ground acceleration distance
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
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Primary Effects of EQs ground motion Fault rupture - very localized
Shaking collapse buildings knock things down bend things
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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
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Estimation of seismic hazard
Max. magnitude/intensity effect at surface estimated fault location
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EQ forecast recurrence interval expected magnitudes all based on
fault assessment historical record earth materials stress field measurements
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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
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EQ hazard reduction mapping research to predict and control EQs
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
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EQ Hazard perception denial acceptance why? response education
experience response move away prepare
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Chapter 6: Volcanic Activity
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Volcanoes Magma rises to surface eruption landform: Paricutin lava
pyroclastics gas landform: Paricutin vent cone caldera rift
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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
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Origins: plate tectonics
mid-ocean ridge hot spots subduction zones
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Volcano Effects Lava flows Aa, slow blocky Pahoehoe, fast ropey
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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
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Volcano Effects gases types emission water vapor CO2 CO, SO2, H2SO4
during eruption during dormancy 1986 Lake Wios, Cameroon heavier than air dissolved in H2O released quickly due to agitation
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Volcano Effects debris flows and mudflows (lahars) Fires
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
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Volcano Effects Caldera - forming eruptions hot springs & geysers
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
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Identification of volcanic hazard
activity active dormant inactive hazardous areas identify effects of previous eruptions examine current conditions
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prediction of eruptions
Geophysical monitoring seismic monitoring magnetic thermal hydrologic topographic changes tilting gas emissions geochemistry quantity geologic history
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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
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Chapter 7: Rivers & Flooding
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Basics of rivers flowing surface water within a channel
source of water – precipitation via: overland flow groundwater
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Basics of rivers basin (watershed) area drained by stream
characteristics size drainage density relief
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Basics of rivers channel shape - width and depth gradient velocity
discharge - volume/time pattern braided - bars sinuous/meandering - fig p 217 pools and riffles
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Basics of rivers sediment load erosion and deposition suspended load
bed load dissolved load erosion and deposition
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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
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Flooding overbank flow causes
precipitation rate (or snowmelt rate) exceeds infiltration capacity, affected by soil/rock type preceding rainfall freezing dam failure
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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
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types of floods upstream downstream ie. 1993 Mississippi flood
short intense rainfall small area dissipate downstream downstream ie 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
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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
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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
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identification of flood prone areas
topography soils wetlands vegetation zones historical development historical floods
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Magnitude and Frequency of Floods
flow events - hydrograph gaging station stage & discharge
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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
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Importance of the flood record
quality of the record more record = better analysis flood deposits vegetation climate change flood populations
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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
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Urbanization & Flooding
alters rainfall to runoff relationship increases drainage density decreases permeability and infiltration capacity results increases frequency increases flood stages flashier floods
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Channelization - fig p 229 adverse effects benefits
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
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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
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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
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special flooding problems
building in the path of over-land flow bank erosion
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perception of flooding
accurate knowledge does not inhibit all development maps not always effective communication upstream development is scapegoat personal knowledge varies
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Chapter 8: Slope Processes, Landslides, and Subsidence
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Mass wasting Down slope movement of material Dynamic material moving
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Classification of slope failures
basis material - rock vs soil water content - wet vs dry rate - slow vs fast shape - rotational vs translational
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Classification of slope failures
types flows - incoherent slides - coherent falls creep subsidence snow avalanche
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factors effecting slope stability
Forces on slope driving vs resisting weight vs shear strength load vs support
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factors effecting slope stability
Material Type Slope angle Climate Vegetation Water (Very important) Addition or removal of slope materials Time
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What causes slope failure?
long-term changes (core cause) trigger – immediate cause vibration (inc. earthquakes) rapid moisture increase addition or removal of slope materials
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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
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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
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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
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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
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Response to unstable slopes
Warning systems surveillance tilt meters geophones Landslide correction stopping active slide removal of water - drainage
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What causes land subsidence?
withdrawal of fluids - oil or water - p mining Karst limestone and dolomite > dissolving rock > loss of rock/H2O > surface collapse
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Land subsidence effects
large areas zones above mines & wells small areas sinkholes above mine shafts & caves
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identification of subsidence-prone areas
look for historical evidence look for danger signs mines soluble rock
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Chapter 9: Coastal Processes
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characteristics of the coast
transitional zone – land & water population concentration coast types erosional vs “depositional” ocean vs Great Lakes
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wave generation wind velocity duration fetch earth movement gravity
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wave types open ocean shallow water - fig p 275 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
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wave erosion water pressure abrasion with sediment entrainment
forms - fig p 281 cliff platform
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wave transportation longshore drift rip currents - fig p 279
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
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beach form - fig p 278 cliff or dune berms (old beach faces) if any
swash zone surf zone breaker zone (longshore bar note zone of littoral transport
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Coastal Erosion causes effects storms human interference
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
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storm surge local rise in sea level added to tide waves on top
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
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tropical cyclones powerful storms damage
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
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Responses to coastal hazards
bear the loss engineering: types groin & jetties seawall, revetment break water beach nourishment & dune building problems enhanced erosion disruption of littoral drift
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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
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