NATURAL HAZARDS - Weebly

NATURAL HAZARDS

What are natural hazards?Natural hazards are extreme natural eventsthat can cause loss of life, extreme damage to property and disrupt human activities.Some natural hazards, such as flooding, can happen anywhere in the world (flooding) happen in specific areas (tropical storms) need climatic or tectonic conditions(tropical storms, volcanic eruptions)

Tropical storms A tropical cyclone is a very powerfullow-pressure weather system whichresults in strong winds (over 120km/h) and heavy rainfall (up to 250mm in one day). In the US and the Caribbean they areknown as hurricanes, in South Asia cyclones, in East Asia- typhoons andin Australia they are known as willy-willies.

Hurricanes need a lot of heat to form and a sea surface temperature of at least 26 C, which iswhy they usually occur over tropical seas.The eye of the storm is formed because thisis the only part of the hurricane where coldair is descending.The air then cools and condenses to formtowering cloudsRising warm air evaporates and starts to spinWarm ocean heats the air aboveIntense low pressure sucks in air, causingvery strong winds

ANATOMY OF A HURRICANECONVECTIONCURRENTSEYEHURRICANE WINDS AND RAINCOOL DENSEAIRWARM MOIST AIR

What are the hazards associated withtropical cyclones? Storm surges Strong winds Torrential rain and flooding

Prediction and preparationRich countries : have resources and technology to predict and monitor storms, ex. using satellites andspecially equipped aircraft. train the emergency services appropriately and to educate people about necessaryprecautions.

Prediction and preparationPoor countries : rely on aid (sometimesreluctantly) from MEDCs intense winds of tropicalstorms can destroy wholecommunities, buildingsand communicationnetworks take longer to recover

Hurricane Katrina Hurricane Katrina was the costliest storm in U.S. history, and its effects are still felt today inNew Orleans and coastal Louisiana.

Katrina first formed as a tropical depressionin Caribbean waters near the Bahamas onAugust 23, 2005. It reached hurricane status two days later,when it passed over south eastern Miami as aCategory 1 storm. The tempest blew through Miami at 80 milesper hour, where it uprooted trees and killedtwo people. Katrina then weakened to a tropical storm,since hurricanes require warm ocean water tosustain speed and strength and begin toweaken over land. However, the storm then crossed back intothe Gulf of Mexico, where it quickly regainedstrength and hurricane status.

On August 27, the storm grew to a Category3 hurricane. At its largest, Katrina was sowide its diameter stretched across the Gulfof Mexico. Before the storm hit land, a mandatoryevacuation was issued for the city of NewOrleans, which had a population of morethan 480,000 at the time. Tens of thousands of residents fled. Butmany stayed, particularly among the city'spoorest residents and those who wereelderly or lacked access to transportation. Many sheltered in their homes or madetheir way to the Superdome, the city's largesports arena, where conditions would soondeteriorate into hardship and chaos.

Officials initially believed NewOrleans was spared. But later that morning, a leveebroke in New Orleans, and asurge of floodwater beganpouring into the low-lying city. An estimated 80 percent ofthe city was soon underwater. The city of New Orleans was ata disadvantage even beforeHurricane Katrina hit. Some ofthe city is below sea level so isparticularly prone to flooding.Low-income communities tendto be in the lowest-lying areas.

Katrina was the most destructive storm to strike the United States and the costliest storm inU.S. history, causing 108 billion in damage. An estimated 1,833 people died in the hurricaneand the flooding. The rescue and recovery efforts following Katrina became highly politicized, with federal,state and local officials pointing fingers at one another. an aging and neglected federal levee system and a slow state and local response following thedisaster

FloodingThere few places onEarth where floodingis not a concern. Anyarea where rain falls isvulnerable to floods,though rain is not theonly cause.The definition of aflood is land coveredby water that is notusually covered bywater.

Causes of floodingNATURAL CAUSES long periods of rain snowmelt impermeable rock(doesn't allow waterthrough) steep slopes overflowing rivers

Causes of floodingCHANGING LANDSCAPE urbanisation (surfaces oftowns and cities areimpermeable ex. tarmac) deforestation broken dams increase in populationdensity (leads to buildingon inappropriate land)

Flooding in BangladeshBangladesh is a low lying country that isincredibly vulnerable to flooding.It has 3 major rivers flowing through it (theGanges, Brahmaputra and Meghna) and isvulnerable to coastal flooding as it is so lowlying and flat.

Flooding in BangladeshBangladesh is a country that has both river and coastal flooding. River floods result from heavy rainfall an melting of snow in the Himalayas. Farmersrely on the floods to supply fine silt (fertile sediment deposited from rivers Coastal floods are created by cyclones which push water in the Bay of Bengal towardsthe land, causing a storm surge. This floods low-lying coastal areas.

WildfiresHow do wildfires start? A fire needs three things: fuel,oxygen and heat. Firefightersoften talk about the fire trianglewhen they're trying to put out ablaze.

On a hot summer'sday when droughtconditions peak,something as small asa spark from a trainwheel striking thetrack can ignite araging wildfire. Sometimes, firesoccur naturally,ignited by heat fromthe sun or a lightningstrike.

Common causes forwildfires include: Arson Campfires Discarding litcigarettes Improperly burningdebris Playing with matchesor fireworks Prescribed fires

Why can they spread so quickly? Once it's started a wildfire can be wind driven, slope driven orfuel driven. Low rainfall causing a drought, searing hottemperatures and wind all make the perfect recipe for a wildfire.

Benefits of wildfires tree cones need to be heated before they open and release their seeds some seeds require fire before they germinate wildfires also help keep ecosystems healthy. They can kill insects anddiseases that harm trees. fires can make way for new grasses that provide food and habitat foranimals and birds they add nutrients to the soil, and open up space to let sunlightthrough to the ground. That sunlight can nourish smaller plants and givelarger trees room to grow and flourish.

AvalanchesMany people think of a snow capped mountain as apeaceful scene, but things can get ugly pretty quick if anavalanche comes!

Avalanches are mostcommon during thewinter, December toApril in the NorthernHemisphere, but they dooccur year-round. To get an avalanche, youneed a surface bed ofsnow, a weaker layerthat can collapse, and anoverlaying snow slab.The highest risk period isduring and immediatelyafter a snow storm.

What causes avalanches?Humans trigger 90 percent of avalanche disasters, with as many as 40 deaths in NorthAmerica each year. Most are climbers, skiers, and snowmobilers.Avalanches are usually triggered by : Heavy snowfall Rise in temperatures People skiing off-piste Strong winds Earthquakes Layers of snow which are not compacted Glacier movement

If you get trapped in an avalanche, it is basically likegetting buried alive. Since the snow is so heavy, avalanche victims are rarelyable to dig themselves out. Once the avalanche stops,the snow settles like concrete and makes it nearlyimpossible to move. Victims of avalanches are also at risk for frostbite, apotentially deadly disease that occurs when the humanbody is exposed to extremely cold temperatures for anextended period of time. Victims are much more likely to survive an avalanche ifthey are rescued within 15 minutes, but after 45minutes the survival rate drops drastically. Besides being dangerous to humans, avalanches canalso cause flash floods and changes in weatherpatterns.

Predicting avalanches

Explosives usedto start smallavalanchesForests to trapsnowRamps and moundsto slow downavalanchesFences to stopavalanchesConcretewedges toprotect pylonsBuildings withreinforced roofs andwalls

Galtur avalancheGaltür is a popular ski resort in Austria. Avalanches happen most years, but don'tusually reach the village of Galtür. On 23 February 1999, an avalanche raceddown the mountain.

Mudslides and landslides A landslide includes a wide range of ground movement, such as rock falls,deep failure of slopes and shallow debris flows. The biggest reason for a landslide is always that there is a slope andmaterial goes down the slope because of gravity.

What triggers landslides? erosion by rivers, glaciers, or ocean waves makes slopestoo steep saturation by snowmelt or heavy rains earthquakes create stresses that make weak slopes fail volcanic eruptions produce loose ash deposits, heavy rain,and debris flows vibrations from machinery, traffic, blasting and eventhunder may trigger failure of weak slopes weight from much rain or snow, or from buildings maystress weak slopes groundwater pressure making the slope unstable removal of deep-rooted plants that bind the soil tobedrock

Vargas tragedyVargas tragedy is one of the worst disaster that struck the Venezuelan country's Vargas state on15 December 1999. It was a result of heavy downpour of rain, flash floods and mudslides

What are natural hazards? Natural hazards are extreme natural events that can cause loss of life, extreme damage to property and disrupt human activities. Some natural hazards, such as flooding, can happen anywhere in the world (flooding) happen in specific areas (tropical storms) need climatic or tectonic conditions (tropical storms, volcanic eruptions)