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 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

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