Natural Disasters

Major Concept:• Earth is a dynamic planet• How do physical events in the environment

affect our health

Although we cannot prevent most natural disasters, there are steps that scientists, engineers, governments, and citizens can take to resist damage and deal with the aftermath.

A landslide caused by the Great Sichuan Earthquake in Sichuan Province, China

EarthquakesEarth’s crust is broken

into large pieces called tectonic plates, which float on a layer of molten rock.

The plates move in different directions

Earthquakes tend to occur along active plate boundaries.

Earthquakes can damage structures and trigger landslides and tsunamis.

Plate TectonicsPlates move at the rate of a few centimeters per year – about the same rate as your fingernails grow.

Asthenosphere convection currents cause the continental plates to move

Plate TectonicsThere are three types of plate boundaries.

Convergent Plate Boundaries

This is when the plates collide

Divergent Plate BoundariesThis is when the plates separate

Transform BoundaryWhen plates slide by each other

California’s San Andreas Fault is a Transform Boundary

San Andreas FaultThe Pacific Plate

(left) west side moves north

The North American Plate (right) east side moves south

WEST

EAST

Oceanic - Oceanic Convergence

Continent - Continent ConvergenceA continent-

continent collision is like a train wreck - both sides end up taking severe damage. Neither side wants to subduct.

The entire Alpine-Himalayan mountain system from Spain to Thailand is behaving this way.

Seismograph

The 1994 Northridge Earthquake

The last major earthquake in Southern California occurred almost twenty years ago

Big quakes release more energy

Earthquakes are found along plate boundaries

Openings in Earth’s crust that eject molten lava and other materials

Ash and gases from volcanic eruptions can block sunlight, causing temperatures to drop.

Eruptions can trigger landslides and mudflows.

Molten lava can cover and destroy surrounding land.

Volcanoes

Did You Know? In 1991, Mount Pinatubo erupted in the Philippines, covering the area around the volcano with a layer of volcanic

materials up to 180 m (600 ft) thick.

VolcanoesMost of the Earth’s active volcanoes on land are located around the Pacific Rim

“Hot Spots”Hawaii and Yellowstone

StormsA storm is a violent disturbance in the

atmosphere4 major types of storms:

ThunderstormsTornadoesHurricanesWinter Storms

A meteorologist is a scientist who studies weather and tries to predict it

Storms

Tornadoes: Rotating funnels of air that can travel over 400 km (250 mi) per hr

Hurricanes: Storms that form over tropical oceans, with winds over 119 km(74 mi) per hour

Thunderstorms: Produce lightning and thunder, usually with heavy rain Did You Know? Hurricane Katrina, which struck

New Orleans in 2005, caused more than $80 billion in damage and killed 1800 people.

ThunderstormsA thunderstorm is a small storm often

accompanied by heavy precipitation and frequent thunder and lightning.

Form in large cumulonimbus clouds (also called thunderheads) on hot, humid afternoons

ThunderstormsWarm, humid air rises

rapidly and the air cools, forming dense thunderhead clouds

Heavy rain falls, sometimes along with hail

Within the thunderhead cloud there are strong updrafts and downdrafts

ThunderstormsLightning heats the air to 30,000oCThunder is the sound of the rapidly heated

air expanding suddenly and explosivelyLight travels faster than sound so you see

lightning before you hear thunder

LightningLightning is a sudden spark, or

electrical dischargePositive and negative charges jump

between parts of a cloud, or between nearby clouds, or between a cloud and the ground

Calculating Lightning DistancesWatch the sky for a flash of

lightning. Count the number of seconds until

you hear thunder. Divide the number of seconds by 5

to calculate the distance the storm is away from your location in miles (or divide by 3 for kilometers).

TornadoesA tornado is a rapidly whirling, funnel-

shaped cloud that reaches down from a storm cloud to touch Earth’s surface

Tornado FormationWarm, moist air flows in at the bottom of a

cumulonimbus cloud and moves upwardA low pressure area forms inside the cloudWarm air rotates as it meets winds blowing

in different directions at different altitudes

Tornado Alley is an area of the United States that has a high frequency of tornadoes because cold, dry air moves south from Canada to meet warm, humid air from the Gulf of Mexico

5 states that cross Tornado Alley are:TexasOklahomaKansasNebraskaIowa

The Fujita Tornado Damage ScaleTornadoes are ranked on the Fujita scale by

the amount of damage they cause

Tornado SafetyA tornado watch is an announcement

that tornadoes are possible in your area. Stay tuned to the radio or television news.

A tornado warning is an announcement that a tornado has been sighted. Take shelter immediately!

The safest place to be during a tornado is in a storm shelter or the basement of a well-built building

Hurricanes A hurricane is a tropical cyclone that has winds of 119 km/h or

higher Hurricanes form in the Atlantic, Pacific, and Indian Oceans In the western Pacific Ocean, hurricanes are called typhoons A hurricane begins over warm ocean water as a low-pressure

area, or tropical disturbance. A hurricane draws its energy from the warm, humid air at the

ocean’s surface As the air rises and forms clouds, more air is drawn into the

system Inside the storm are bands of very high winds and heavy rains Winds spiral inward toward the area of lowest pressure at the

center

Hurricane Formation

HurricanesHurricanes last longer than other storms, usually

a week or moreAfter a hurricane passes over land, it no longer

has warm, moist air to draw energy from so it loses strength

A storm surge is a “dome” of water that sweeps across the coast where a hurricane lands

For safety during a hurricane, people are told to evacuate

Evacuate means to leave the area immediately

                                                             

Winter StormsAll year round, most precipitation begins in

clouds as snowA large amount of humid air that cools below

0oC can produce a winter stormBlizzard = Blowing snow and reduced visibilityMain Hazards

Vehicle accidentsHypothermiaExertionImmobility

Avalanches

Masses of snow that slide down a slopeConditions favoring avalanches:

Slope greater than 30 degreesUnstable snowpackHeavy snowfallWarm temperatures

Did You Know? A big North American avalanche can contain 230,000 m3 of snow—about the equivalent of 20 football fields filled with snow 3 m (10 ft) deep.

ImpactsMain direct impacts

are deaths, injuries, and economic losses to communities affected.

Indirect impacts include wider economic losses to tourism industry, transport delays, and wider spatial economic losses.

Contributing factorsHeavy rainfall on snow

(more likely in Scotland than the Alps!)

Deforestation - reducing slope stability

Vibrations – skiers or more dangerous earth movements

Long cold winters then heavy snow falls in spring. i.e. slip plane created.

Snow-pack StressSnow lying on a slope is subject to stress : gravity is pulling it downwardsadhesion and weight is keeping it “stuck” to the

slope.Often these stresses are delicately balanced, and a

slight change can bring about failure, particularly where the snow-pack is under tension.

Powder snow avalanches

No warning.Up to 200mphUp to 50

tons/m 2 forceOccur at any

time in season.Example :Galtu

r, Austria.

Wet snow avalanchesUsually late in

season.Slow moving (5-

15mph).Considerable

weight of wet snow (up a million tonnes).

Example : Odda, Norway.

Slab avalanchesSlab avalanches

are most common occurrence.

Often started by human error.

Most frequent cause of death amongst skiers, snowboarders, and power-skiers.

Speeds up to 100mph.