Natural Disasters Final

Flash Flood

Sudden flooding caused by intense rainfall; deadliest flood type in the U.S.

Regional Flood

Flooding over large areas after long lasting rainfall

Percent of U.S. on floodplains

10%

1972 deadly flash flood location

Rapid City, South Dakota

Flood frequency principle

Small floods occur more often than large floods

Causes of killer floods

Thunderstorms, prolonged rain, hurricanes, ice breakup, and snow melt

1993 upper Mississippi floods

Caused by persistent heavy rainfall and saturated soil

Why lower Mississippi not badly flooded in 1993

Ohio river input was low

1993 eastern U.S. conditions

High pressure and drought

Huang (Yellow) River nickname

River of sorrow

Avulsion

Sudden change in river course

Living successfully with floods requires

Understanding stream discharge, sediment, slope, and channel shape

independent stream variables

Water discharge, sediment load, and slope

Dependent stream variables

Velocity, channel shape, erosion/deposition

Base level

Lowest elevation a stream can a road to (usually sea level)

Stream equilibrium

Balance between discharge, settle, slope, and sinuosity

Too much discharge response

Increased meandering and sinuosity

Too much sediment, too little water

Braided stream

Hydrograph

Graph of stream discharge vs time

Rising limb (hydrograph)

Water going up

Falling limb (hydrograph)

Decreasing discharge after peak flow (water going down)

Urban hydrograph

Higher, faster flood peaks

Rural hydrograph

Lower, slower flood peaks

Urban flooding causes

Pavement, buildings, storm sewers

Recurrence interval (RI)

Average time between floods of similar size

10 year flood meaning

10% chance of occurring in any given year, if a flood has a 10 year reoccurrence interval it means a similar flood has a 1/10 chance of occurring in the same year

RI formula, what N and M stand for

RI=(N+1)/M, M=Rank of flood event, N= Number of years of record

Why are levees controversial

They raise flood heights and increase damage if they fail

Channelization effect

Increases gradient and water velocity

Best flood management

Flood frequency curves, education, land use planning

Mass movement

Downslope movement of rock, soil, or debris due to gravity

Shear force

Force pulling material downhill

Normal force

Force perpendicular to slope

Friction

Resistance preventing movement

Effect of steeper slope

Shear force increases

External triggers of landslides

Rain, earthquakes, volcanoes, wildfires, floods, construction

Most catastrophic landslide trigger

Earthquakes

Factors controlling mass movement

Geology, climate, terrain, water content

Material most associated with earth flows

Clay minerals

Pre existing slope weakening conditions

Faults, fractures, bedding planes, clay layers, saturation

Basis of mass movement classification

Type of material, type of movement, speed

Rock fall

Free falling rock; fastest mass movement

Translational slide

Movement along flat plane of weakness

Rotational slide (slump)

Curved sliding surface

Earthflow

Slow, viscous flow of clay rich material

Debris flow

Fast moving mixture of water, rock, soil

Slowest mass movement

Creep

Translational slides move along planes of

Weakness

Translational slide example

Point Fermin, CA

Earthflow example

Portuguese Bend, CA

Slump example

La Conchita, CA

Long runout debris flow example

Blackhawk event (CA) and Elm, Switzerland

Rick fall example

Yosemite valley

Submarine landslide hazard

Tsunami generation

Snow related slope failures

Avalanches

Avalanche triggers

Snow load, slope angle, temperature change, vibration

Sinkholes occur in

Limestone and soluble rocks

Why limestone dissolves

Carbonic acid reaction with calcium carbonate

Houston-Galveston subsidence cause

Groundwater withdrawal

Landslide mitigation

Drainage, retaining walls, vegetation, slope avoidance, monitoring

Tsunami

Long wavelength waves caused by sudden sea floor displacement

Tsunami causes

Fault movement, volcanoes, landslides, meteor impacts

Fault movement example

2004 Sumatra earthquake

Volcanic eruption example

Krakatoa (1883)

Landslide example

Lituya Bay, Alaska

Canary Islands threat

Volcanic flank collapse could affect U.S. East Coast

2004 tsunami ocean

Indian Ocean

Most deaths in 2004

Indonesia

Tectonic setting

Subduction zone

1883 Indian Ocean tsunami cause

Krakatoa eruption

Why ships don’t notice tsunami in deep ocean

Very small wave height

Tsunami wavelength

Hundreds of kilometers

Tsunami speed

Up to 800km/hr (500mph)

Tsunami wave arrival

Series of waves every 10-60 minutes

Most destructive waves

Cannot be predicted

Why tsunamis grow near shore

Slowing speed increases wave height

Tsunami vs wind waves

Tsunami: long wavelength, full water column

Wind waves: short wavelength, surface only

1946 April fool’s tsunami epicenter

Aleutian Islands, Alaska

1960 M9.5 earthquake

Chile

Chile tsunami impacts

Chile, Hawaii (14hrs), Japan (22.5hrs)

1700 Pacific Northwest earthquake

Cascadia subduction zone

Why trees died after 1700 EQ

Land subsidence and saltwater flooding

Evidence of future Cascadia EQ

Tree rings, Japanese tsunami records

Largest tsunami run up

Lituya bay, Alaska

Tsunami warning signs

Sea withdrawal, loud ocean noise

Best tsunami response

Move to higher ground immediately

Weather

Short term atmospheric conditions

Climate

Long term atmospheric conditions

Radiation

Energy emitted as waves or particles

Why sun emits shortwave radiation

Higher temperature

Why earth emits long wave radiation

Lower temperature

Main greenhouse gases

CO2, CH4, N2O, H2O Vapor

Greenhouse effect

Trapping of heat in atmosphere

Greenhouse gases vs effect

Gases cause the effect

Largest contributor to global warming

CO2

Do greenhouse gases absorb long wave radiation

Yes

Why climate change is controversial

Economic, political, energy policy impacts

Anthropogenic climate change

Caused by human activity

Carbon isotope evidence

Fossil fuels have distinct 12C, 13C, 14C ratios

Low 18O/16O ratios indicate

Cold climate