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Chapter 4 - Natural Hazards: An Overview Effects of hazards on humans scope: $50 billion/year avg 150,000 dead/year social loss - employment, anguish, productivity humans located in the way of natural processes Problems hazardous zones complex response & threshold crossings dramatic effect of “small”hazard effects between tectonic plates between land and water - population centers biological geological meteorological 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 Service functions: natural results of processes nutrients to flood plains sediment to beaches flushing of pollutants (often end up elsewhere) landslide dams for lakes sinkholes form ponds volcanoes create new land add nutrient rich ash support life earthquakes affect ground water lift mountains 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 importance is debated by geologists esp. with respect to long term development of earth’s surface and uniformitarianism table p 106 Evaluation of hazards purpose - to minimize loss methods identify susceptible areas - probability of occurrence based on past events - history of area studies of process understanding of geology linkages physical location scale global regional local Evaluation of Hazards prediction forecast general location magnitude range chance of occurrence not specific ratio = 1:100 or 100 yr flood percent - 50% over next 15 yrs warning – this will happen specific time place magnitude based on precursors non or pseudo science beware ie heavy rain = flood often wrong certain to be correct occasionally dangers boy who cried wolf affects people and businesses Scientists, media, & Hazards media - human impact scientists conservative reluctant to make statements without disclaimers based on it is likely lack 100% agreement communication problems Risk assessment probability x consequences qualitative - determine factors quantitative Acceptable risk based on assign # values to risk # values may be hard to determine 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 land use planning identification and probability predictions and forecasts risk assessments 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 types Dip slip former plate boundaries Addition or removal of material 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 Seismic activity Identification of activity date movements of soils and other features study stress field and measure stain trench across fault other portions (segments of fault) top seds are not offset 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 S-wave fastest 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 ground acceleration material - most intense in unconsolidated material!!! directivity - most intense in direction of fault rupture acceleration of ground as EQ waves pass horizontal & vertical distance depth of focus horizontal distance 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 Primary Effects of EQs ground motion Fault rupture - very localized Shaking collapse buildings knock things down bend things Secondary effects of EQs liquefaction landslides fires - broken power and gas lines - result loss of life water bodies water saturated material material acts as a liquid tsunamis - long wavelength, fast seiches changes in land elevation disease Estimation of seismic hazard Max. magnitude/intensity soil/bedrock conditions estimated fault location Probability 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 radon gas release may increase seismic gaps (locked fault magnetic fluctuations electrical resistivity rates of uplift or subsidence varies with earth materials, groundwater, and others changes before EQ animal behavior not reliable could relate to other precursors EQ prediction Prediction models stress buildup and avg recurrence med to long term probabilities not certainties 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 lava extruded - eruption Eruption type Gas content (hi gas = explosive Si content (hi Si content = explosive hi viscosity = explosive pyro clastic landform vent cone caldera rift volcano types and eruption manner - table p 176 Shield - quiet Cinder - explosive Composite - quiet/explosive Volcanic domes - explosive Flood basalts - quiet Origins mid-ocean ridge hot spots subduction zones 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 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 Identification of volcanic hazard activity active dormant inactive hazardous areas identify effects of previous eruptions examine current conditions prediction of eruptions Geophysical monitoring hydrologic topographic changes tilting gas emissions seismic monitoring magnetic thermal 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 engineering/legal definition formed by migration of river overbank deposition includes natural levees 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 warming 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 - mat’l moving down) Elements - fig p 243 crest - convex free face debris slope wash slope - concave Classification of slope failures basis material - rock vs soil water content - wet vs dry rate - slow vs fast shape - rotational vs translational types flows - incoherent slides - coherent falls creep subsidence snow avalanche factors effecting slope stability Forces on slope driving vs resisting weight vs shear strength (W + Mass X Gravity load vs support Material Type soil & weak rock - rotational and frequent strong rock - translational & infrequent orientatation of layers - (esp w/ planes of weakness factors effecting slope stability Slope and topography slope angle - steeper = more slides low = slips = slow processes steep = falls, avalanches - fast processes more energy Climate moist flows, wet, weathering, material removal factors effecting slope stability Vegetation positive & negative provides cover roots – binding & breaking removes water adds weight concerns vegetation type hydrophobic soils: infiltration retarded due to fire causing waxy organics to accumulate loss of vegetation factors effecting slope stability Water (Very important) weathering reduces shear strength quantity - dry, moist, saturated increase = >pore pressure - decrease shear strength, > weight rainfall & snowmelt liquefaction of clay loss of shear strength due to disturbance seepage of water onto slopes removal of slope by erosion, and humans Time seasonal changes reduction in strength What causes slope failure? long-term changes (core cause) trigger – immediate cause EQ’s vibration rapid moisture increase What causes slope failure? external increase shear stress loading steepening shock internal reduce shear strength increase water pressure decrease in cohesion slopes and humans humans building in the way enhanced by humans - humans induce longterm changes and triggers timber harvesting urbanization/development - fig p 256 septic fields loading toe removal humans create unstable situations Hazard recognition slope stability maps geology slope angle % of slope 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 Preventiing 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 compaction due to lower fluid pressure cannot reverse uniform materials mining - coal, fluid, salt, other Karst - limestone and dolomite, dissolving rock, loss of rock/H2O Land subsidence effects large areas - zones above mines & wells sinkholes identification of subsidenceprone areas look for historical evidence look for danger signs mines soluble rock Chapter 9: Coastal Processes characteristics of the coast Transitional zone - continent and coast 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 rip currents - fig p 279 wave erosion water pressure abrasion with sediment entrainment forms - fig p 281 cliff platform wave transportation longshore drift sediment moves along the coast because waves approach at a slight angle constant movement 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 high pressure push water onto coast added to tide waves on top moves waves farther on shore 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 types Groin seawall, revetment break water jetties 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