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Chapter 4 - Natural Hazards: An Overview. Effects of hazards on humans scope: $50 billion/year average of 150,000 dead/year social loss - employment,

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Presentation on theme: "Chapter 4 - Natural Hazards: An Overview. Effects of hazards on humans scope: $50 billion/year average of 150,000 dead/year social loss - employment,"— Presentation transcript:

1 Chapter 4 - Natural Hazards: An Overview

2 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

3 Problems hazardous zones: geologically active good vs bad - depends on POV few if any places are free from all hazards

4 magnitude and frequency magnitude: size of event frequency: recurrence interval % chance per year hi magnitude, low frequency usually most dangerous

5 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

6 Evaluation of hazards purpose - to minimize loss methods: identify susceptible areas based on: past events - history of area studies of process physical location

7 Evaluation of Hazards media - human impact scientists conservative reluctant to make statements without disclaimers based on it is likely lack 100% agreement communication problems

8 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 prediction 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

9 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

10 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

11 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

12 Climate change, land use change, and hazards effects floods, erosion, landslides, drought, fires alters locations and probabilities normal, long-term change

13 Population increase and natural hazards increases demands on land and resources pushes people into marginal areas

14 Chapter 5: Earthquakes & Related Phenomena

15 EQ features epicenter hypocenter (focus) seismic waves fault rupture below ground surface

16 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

17 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

18 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

19 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

20 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

21 Seismic Waves Body waves - hi freq hz P-wave fastest S-wave thru solid only Surface waves - lo freq <1hz Love - shear (side to side) Rayleigh - oscillation - fig p 139

22 Seismology Measuring seismic waves seismograph seismic station seismogram Location by triangulation S&P wave arrivals Distance radios for 3 stations

23 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

24 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

25 Primary Effects of EQs ground motion Fault rupture - very localized Shaking collapse buildings knock things down bend things

26 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

27 Estimation of seismic hazard Max. magnitude/intensity effect at surface estimated fault location

28 EQ forecast recurrence interval expected magnitudes all based on fault assessment historical record earth materials stress field measurements

29 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

30 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

31 EQ Hazard perception denial acceptance why? education experience response move away prepare

32 Chapter 6: Volcanic Activity

33 Volcanoes Magma rises to surface eruption lava pyroclastics gas landform: ParicutinParicutin vent cone caldera rift

34 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

35 Origins: plate tectonics mid-ocean ridge hot spots subduction zones

36 Volcano Effects Lava flows Aa, slow blocky Pahoehoe, fast ropey

37 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

38 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

39 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

40 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

41 Identification of volcanic hazard activity active dormant inactive hazardous areas identify effects of previous eruptions examine current conditions

42 prediction of eruptions Geophysical monitoring seismic monitoring magnetic thermal hydrologic topographic changes tilting gas emissions geochemistry quantity geologic history

43 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

44 Chapter 7: Rivers & Flooding

45 Basics of rivers flowing surface water within a channel source of water – precipitation via: overland flow groundwater

46 Basics of rivers basin (watershed) area drained by stream characteristics size drainage density relief

47 Basics of rivers channel shape - width and depth gradient velocity discharge - volume/time pattern braided - bars sinuous/meandering - fig p 217 pools and riffles

48 Basics of rivers sediment load suspended load bed load dissolved load erosion and deposition

49 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

50 Flooding overbank flow causes precipitation rate (or snowmelt rate) exceeds infiltration capacity, affected by soil/rock type preceding rainfall freezing dam failure

51 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

52 types of floods upstream 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

53 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

54 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

55 identification of flood prone areas topography soils wetlands vegetation zones historical development historical floods

56 Magnitude and Frequency of Floods flow events - hydrograph gaging station stage & discharge

57 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

58 Importance of the flood record quality of the record more record = better analysis flood deposits vegetation climate change flood populations

59 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

60 Urbanization & Flooding alters rainfall to runoff relationship increases drainage density decreases permeability and infiltration capacity results increases frequency increases flood stages flashier floods

61 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

62 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

63 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

64 special flooding problems building in the path of over-land flow bank erosion

65 perception of flooding accurate knowledge does not inhibit all development maps not always effective communication upstream development is scapegoat personal knowledge varies

66 Chapter 8: Slope Processes, Landslides, and Subsidence

67 Mass wasting Down slope movement of material Dynamic material moving

68 Classification of slope failures basis material - rock vs soil water content - wet vs dry rate - slow vs fast shape - rotational vs translational

69 Classification of slope failures types flows - incoherent slides - coherent falls creep subsidence snow avalanche

70 factors effecting slope stability Forces on slope driving vs resisting weight vs shear strength load vs support

71 factors effecting slope stability Material Type Slope angle Climate Vegetation Water (Very important) Addition or removal of slope materials Time

72 What causes slope failure? long-term changes (core cause) trigger – immediate cause vibration (inc. earthquakes) rapid moisture increase addition or removal of slope materials

73 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

74 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

75 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

76 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

77 Response to unstable slopes Warning systems surveillance tilt meters geophones Landslide correction stopping active slide removal of water - drainage

78 What causes land subsidence? withdrawal of fluids - oil or water - p mining Karst limestone and dolomite > dissolving rock > loss of rock/H2O > surface collapse

79 Land subsidence effects large areas zones above mines & wells small areas sinkholes above mine shafts & caves

80 identification of subsidence- prone areas look for historical evidence look for danger signs mines soluble rock

81 Chapter 9: Coastal Processes

82 characteristics of the coast transitional zone – land & water population concentration coast types erosional vs “depositional” ocean vs Great Lakes

83 wave generation wind velocity duration fetch earth movement gravity

84 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

85 wave erosion water pressure abrasion with sediment entrainment forms - fig p 281 cliff platform

86 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

87 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

88 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

89 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

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94 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

95 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

96 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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