Natural Disasters midterm 3

Tsunami

Series of long period ocean waves caused by water displacement from impulsive events

Tsunami causes

• Earthquakes

• Volcanoes

• Landslides

• Meteors

Tsunami source: Earthquakes

Caused by EQs that disrupt sea floor, large vertical movement, mostly occur at subduction zone (ex. Megathrust EQs)

Tsunami sources: Volcanoes

Caldera collapse, pyroclastic flow/volcanic landslide entering ocean, explosive underwater eruptions

Tsunami sources: landslides

Terrestrial landslides into ocean, underwater slumps and landslides

Peaks and Troughs

Peak: water rises

Troughs: water recedes

Leading Trough

Water withdraws, sometimes for many minutes, draws people onto beach into path of wave

Tsunami propagation

• prograde elliptic particle motion

Deep water waves

D>lambda/2

Particle motion unaffected by seafloor

Shallow water waves

D<lambda/2

Particle motion affected by seafloor

Seafloor wavelengths

Lambda= 10-1000km

Period=10-60mins

Buildings in Tsunamis

• crushed by water pressure

• Collapse due to ground erosion

Other Tsunami Hazards

• contaminants spread by waves (sewage/hazardous materials)

• Leads to disease and fire

• Drowning

• Debris

Weather

Meteorological conditions at a current space/time

Climate

Meteorological conditions over a long period of time (trends, regional)

Climate change: natural causes

Plate tectonics, ocean circulation, orbital eccentricity

Orbital tilt

Change in inclination of earths spin axis

Orbital Wobble

Change in spin axis direction

Greenhouse effect

Solar radiation trapped by gag instead of reflected

Anthropogenic global warming

Burning fossil fuels, methane, nitrous oxide, ozone, chlorofluorocarbons

Global climate change

• uneven temperature increased

• More severe/frequent extreme weather events

Thunderstorm hazards

• lightning

• Fire

• Hail

• Winds

• Rain/flash floods

Thunderstorm: early stage

Warm, moist, air heated near ground rises. Water vapour condenses

Condensation releases uplifting air mass

Thunderstorm: mature stage

Droplets/ice crystals become heavy and precipitate

Updrafts and downdrafts occur causing winds, hail, rain, lightning, etc

Thunderstorms: dissipating phase

• downdrafts drag in cool, dry air

• Thunderclouds evaporate

Lightning

100 strikes per second

Electrical charge separation in thunderclouds

Collisions transfer

Tornadoes

• most intense with winds up to 500km/hr

• Most in summer months

• Fujita scale (classification. F0=Light, F5=complete destruction)

Hurricane

Powerful rotating low pressure system

Hurricane formation

Warm sea surface

Warm humid unstable air

Weak upper level wind

Coriolis force from earths rotation

Coriolis force

Because of earths rotation

Increases towards poles

Moving objects directed right in N hemisphere, left in S hemisphere

Cyclonic flow

Pressure gradient

Coriolis force

Centrifugal force

Friction

Stages in hurricane formation

1. Tropical disturbance

2. Tropical depression

3. Tropical storm

4. Hurricane

Hurricane eye

Circular region of calm weather in centre of hurricane, surrounded by eye wall

Storm surges

Rise in sea level due to

• strong onshore winds

• Low pressure

• Great damage