What’s it all

about?

DE LA SALLE COLLEGE Geography Department

Ms.Diane Sammut

TOPIC 2

NOTES

Natural Hazards

2

We will be focusing on...

Page

What are natural hazards? 3

Understanding tropical storms 4

Hurricanes—Preparation and prediction 7

CASE STUDY—Hurricane Katrina 8

Investigating flooding 10

CASE STUDY—Flooding in Bangladesh 12

Burning wildfires 15

Moving snow —Avalanlches 17

CASE STUDY—Galtür avalanche 19

It’s raining mud —Mudslides 20

CASE STUDY —Vargos tradgedy 21

Glossary 22

This topic will be addressing the following learning outcomes :

8.1 I can research a case study to describe the characteristics and effects of any one of the following types of natural disasters such as hurricanes, flooding, tsunami, wildfires, sandstorms, avalanches and blizzards.

3

What are NATURAL HAZARDS ?

Imagine you're swimming on a beautiful summer day

at the beach, building a funny-looking snowman in

winter, or strolling through the woods on a crisp

autumn day. In scenes like these, the natural world is

wonderful, beautiful and as enjoyable as can be. But

nature can also be terribly harsh. Things like monster

storms, volcanoes, major earthquakes, tremendous

floods and fires are examples of natural disasters that

cause widespread destruction and often turn deadly.

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. Other natural hazards, such as

tornadoes, can only happen in specific areas. And

some hazards need climatic or tectonic conditions to

occur, for example tropical storms or volcanic

eruptions.

Human activities can

influence how often

certain natural hazards

occur and how severe

they are. Understanding when, where, why and how

natural hazards occur can help us to understand how

to minimise their impact on our lives.

TYPES OF NATURAL HAZARDS

Natural hazards can be placed into two categories -

tectonic hazards and climatic hazards.

Tectonic hazards occur when the Earth's crust

moves. For example, when the plates move, friction

can cause them to become stuck. Tension builds until

the plates release, which leads to an earthquake.

Climatic hazards occur when a region has certain

weather conditions, for example heavy rainfall can

lead to flooding.

4

Understanding TROPICAL STORMS A tropical cyclone is a very powerful low-pressure

weather system which results in strong winds (over

120 km/h) and heavy rainfall (up to 250 mm in one

day). Tropical cyclones have different names

depending on where they occur in the world. In the

US and the Caribbean they are known as hurricanes,

in South Asia - cyclones, in East Asia- typhoons and

in Australia they are known as willy-willies. They all

develop in the same way and have the same

characteristics.

In appearance, a tropical cyclone is like a huge

whirlpool - a gigantic mass of revolving moist air.

Tropical cyclones (or storms) are between 482-644

kilometres wide and 6-8 km high. They move

forward at speeds of 16-24 km/h, but can travel as

fast as 65 km/h.

In an average year over a dozen hurricanes form over

the Atlantic Ocean and head westwards towards the

Caribbean, the east coast of Central America and the

southern USA (Florida in particular), and may last as

long as a month. Tropical storms are defined by their

wind speeds and the potential damage they can

cause, using what is known as the Saffir Simpson

scale.

Map showing the area which are most prone to tropical storms.

5

HOW HURRICANES FORM?

Hurricanes need a lot of heat to form and a sea surface temperature of at least 26°C, which is why they

usually occur over tropical seas. They also need to be between 5 and 20° north or south of the Equator. It works

like this:

A

B

C

D

E

6

WHAT ARE THE HAZARDS ASSOCIATED WITH

TROPICAL CYCLONES?

When a tropical cyclone arrives at a coastline, it is

potentially fatal and can cause damage to property.

This is because tropical cyclones bring with them:

Storm surges – these are huge surges of high

water up to 3 metres in height that sweep inland

from the sea, flooding low-lying areas.

Strong winds – winds of over 120 km/h (75 mph)

blow inland, which are capable of causing

significant damage and disruption, for example by

tearing off roofs, breaking windows and damaging

communication and transport networks.

Torrential rain and flooding – the warm, humid

air associated with a tropical cyclone produces

very large amounts of rainfall, often in excess of

200 mm in just a few hours. This can cause short-

term flash flooding, as well as slower river

flooding as the cyclone moves inland.

The damage in the Bahamas caused by hurricane Dorian (2019)

ANATOMY OF A HURRICANE

Hurricane Dorian (2019)

7

HURRICANES—Preparation and prediction Preparation and prediction techniques can be very

different in MEDCs and LEDCs (more/less

economically developed countries).

MEDCs have the resources and technology to

predict and monitor the occurrence of storms, ex.

using satellites and specially equipped aircraft. They

are also equipped to train the emergency services

appropriately and to educate people about

necessary precautions.

Storm warnings can be issued to enable the

population to evacuate or prepare themselves for

the storm. People can prepare by storing food and

water or boarding up their windows.

LEDCs are often less prepared. They may rely on

aid (sometimes reluctantly) from MEDCs for the

rescue and recovery process. The intense winds of

tropical storms can destroy whole communities,

buildings and communication networks. As well as

their own destructive energy, the winds generate

abnormally high waves and tidal surges. Sometimes

the most destructive elements of a storm are the

subsequent high seas and flooding.

MEDCs are better placed to reduce the effects of

tropical storms because they have more financial,

educational and technological resources to help

deal with them. They better able to observe and

predict storm behaviour and can invest in

infrastructure to withstand storms - as well as

spending more money on repairing the damage

caused.

People fixing window shutters in preparation of hurricane season. People stocking up their needs for when the hurricane hits.

8

CASE STUDY—Hurricane Katrina

Hurricane Katrina is tied with Hurricane Harvey (2017) as the

costliest hurricane on record. Although not the strongest in

recorded history, the hurricane caused an estimated

$125 billion worth of damage. The category five hurricane is

the joint eight strongest ever recorded, with sustained winds of

175 mph (280 km/h).

The hurricane began as a very low-pressure system over the

Atlantic Ocean. The system strengthened forming a hurricane

which moved west, approaching the Florida coast on the

evening of the 25th August 2005.

IMPACTS

Katrina was a category 4 storm.

Storm surges reached over 6 metres in

height.

New Orleans was one of the worst

affected areas because it lies below

sea level and is protected by levees.

These protect it from the Mississippi

River . The levee defences were unable

to cope with the strength of Katrina,

and water flooded into the city.

Despite an evacuation order, many of

the poorest people remained in the

city.

People sought refuge in the Superdome

stadium. Conditions were unhygienic,

and there was a shortage of food and

water. Looting was commonplace

throughout the city. Tension was high

and many felt vulnerable and unsafe.

1 million people were made homeless

and about 1,200 people drowned in the

floods.

Oil facilities were damaged and as a

result petrol prices rose in the UK and

USA. The storm caused oil spills .

1.3 million acres (5,300 km2) of forest

lands were destroyed costing about

$5 billion.

The lands that were lost were breeding

grounds for marine mammals, brown

pelicans, turtles, and fish

Racial tensions were exposed and

intensified, as many of the victims were

black African Americans. Four days after Hurricane Katrina made landfall on the Gulf Coast, many parts of New Orleans remain flooded.

9

RESPONSES

There was much criticism of the

authorities for their handling of the

disaster. Although many people were

evacuated, it was a slow process and the

poorest and most vulnerable were left

behind.

Of the 60,000 people stranded in New

Orleans, the Coast Guard rescued more

than 33,500.

$50 billion in aid was given by the

government.

However, only one-fifth of the housing

units requested in Orleans were

supplied, resulting in an enormous

housing shortage in the city of New

Orleans. To provide for additional

housing, government has also paid for

the hotel costs of 12,000 individuals and

families displaced by Katrina.

The UK government sent food aid during

the early stages of the recovery process

while Kuwait made the largest single

pledge, $500 million.

The National Guard was mobilised to

restore and maintain law and order in

what became a hostile and unsafe living

environment.

People wade through high water in front of the Superdome in New Orleans.

New homes built along the rebuilt Industrial Canal levee.

Police watch over prisoners who were evacuated to a highway.

Water spills over the levees in the aftermath of hurricane Katrina

10

Investigating FLOODING

There few places on Earth where flooding is not a

concern. Any area where rain falls is vulnerable to

floods, though rain is not the only cause.

The definition of a flood is land covered by water

that is not usually covered by water. Excessive

rain, a damaged dam or levee, rapid melting of snow

or ice, can make a river, spread over nearby land.

Coastal flooding occurs when a large storm

or tsunami causes the sea to surge inland.

Most floods take hours or even days to develop,

giving residents time to prepare or evacuate. Others

generate quickly and with little warning. So-

called flash floods can be extremely dangerous,

instantly sweeping everything in their path

downstream.

Climate change is increasing the risk of floods

worldwide, particularly in coastal and low-lying

areas, because it is increasing extreme weather

events and rising seas. The increase in temperatures

that accompanies global warming can contribute

to hurricanes that move more slowly and drop more

rain. Meanwhile, melting glaciers and other factors

are contributing to a rise in sea levels that has created

long-term, flooding risks for places ranging

from Venice, Italy to the Marshall Islands. More than

670 U.S. communities will face repeated flooding by

the end of this century, according to a 2017 analysis;

it's happening in more than 90 coastal communities

already.

People walk on a catwalk in a flooded St. Mark's Square during a period of seasonal high water in Venice, Italy .

NATURAL FACTORS CHANGES IN LANDSCAPE

Flooding can occur as a result of natural factors or be influenced by changes made to the landscape.

What are the main effects of flooding?

PRIMARY EFFECTS (immediate) SECONDARY EFFECTS (long-term)

11

Flooding often leads to loss of life as a result of

heavy flooding, causing emotional trauma for those

who have gone through it. Even if people have not

been directly affected by the loss of life, losing

property, houses, or land can cause physiological

damage. Especially if the people affected are unable

to rebuild due to the houses being too badly damage,

farm land being filled with salt water, or lack of

resources to rebuild, many find the recovery to be

more than just physical.

Damage to property during flooding is often

extensive. Vehicles should not be driven through

flooded areas, but often they are caught unaware,

creating the need for replacement or extensive

repairs. Houses that have been flooded mildly might

survive with just a good cleaning, but big floods often

render homes unlivable without massive repairs or

restructuring. Many personal items are lost forever,

such as paper documents, photographs, clothing, and

household items. Furniture and woodwork are often

damaged beyond repair and must be replaced entirely.

In severe floods, communication systems can fail

due to lines being broken. Power is often hindered if

power generators and transmission is in some way

destroyed or damaged. Getting power restored after a

flood is challenging as water transmits electricity and

can hurt anyone standing in water. If sewage or water

systems are compromised during flooding, water

supplies can be contaminated. This can result in

waterborne diseases such as typhoid or cholera

among others.

Land that has be saturated often cannot grow new

crops for some time. If the water was saline, such as

in flooding near the sea, land will not be able to be

cultivated for some years. Loss of livestock can also

result in farmers losing their livelihood and needing

to start over with young animals means losing the

profit that would have come during that time. Any

livelihood that depends on farming or ranching can be

seriously affected by floods as farms and ranches

often need to be near a body of water in order to live.

South Dakota residents are dealing with a flooding nightmare.

Cattle in a flooded field in the UK.

2015 South Indian floods .

12

CASE STUDY—Flooding in Bangladesh Bangladesh is a country that has both river and

coastal flooding.

River floods result from heavy rainfall an melting

of snow in the Himalayas. Farmers rely on the

floods to supply fine silt (fertile sediment

deposited from rivers) to the land, making it fertile

and good for the growth of crops.

Coastal floods are created by cyclones which push

water in the Bay of Bengal towards the land,

causing a storm surge. This floods low-lying

coastal areas.

THE 2004 FLOODS

The 2004 floods were devastating to Bangladesh.

At their peak they covered over half of the country

and affected wo-thirds of the population. In many

places only the tops of trees and buildings could be

seen.

THE IMPACTS

Serious river flooding occurred after heavy rainfall

in July and August which resulted in :

destroyed over 8.5 million homes and made 35

million people homeless.

The official death toll was put at over 760 with

many others reported as missing. Most deaths

were due to drowning but others were to occur

later from diseases such as cholera.

Then in September, Bangladesh had its heaviest

rainfall for 50 years. In just one day Dhaka, the

capital had 35cm of rainfall (two-thirds of

London’s average annual total).

This led to :

Floodwater up to 2 metres deep covered

the city.

Electricity was cut off for several weeks;

Water in wells was polluted making it

unsafe to drink and children caught fish in

the city streets;

Small villages were cut off;

Rice plants , sugar cane and vegetable crops

washed away and lost;

Thousands of kilometres of roads, a third of

the railway and Dhaka’s international airport

were all flooded. This made it impossible to

deliver emergency food and medical

supplies.

There was little immediate help from overseas as

global attention was fixed in flooding caused by

hurricanes in the USA.

13

WHAT HAS BANGLADESH DONE TO COPE WITH

FLOODING?

Bangladesh is a very poor country and so has less

money to spend on flood defences than richer

countries. Most people in Bangladesh do not earn

enough to pay for insurance against flooding, so

when there are floods they risk losing everything.

SHORT-TERM RESPONSES TO FLOODING

Food aid from the Government and other

countries.

Water purification tablets.

People repaired embankments and helped to

rescue people.

Free seeds given to farmers.

LONG-TERM RESPONSES Building embankments.

Building raised flood shelters.

Introducing flood warning systems.

Emergency planning.

Dams planned.

Reducing deforestation.

Unfortunately, many of these long-term responses are

difficult to pay for and maintain. They are not always

People cut off due to flooding.

City roads completely flooded in 2004.

14

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15

Burning WILDFIRES

A wildfire is an uncontrolled fire that burns in the

wildland vegetation, often in rural areas. Wildfires

can burn in forests, grasslands, savannas, and other

ecosystems, and have been doing so for hundreds

of millions of years. When a heat wave or drought

dries out the plants in an area, a fire can start and

spread quickly. Fires can be accidental or they can

be caused by arson or even lightning strikes.

Because fires can be very destructive, fire-fighters

have developed lots of strategies for extinguishing

or controlling wild fire. However, fire can also

play an important role in the life cycle of plants

and habitats.

WHERE DO THEY HAPPEN?

Wild fires take place all over the world. Major

fires happen every few years in the forests of the

United States and Indonesia, and in the bush in

Australia, however they are also common in

Europe.

WHERE DO THEY START?

The weather has to be really hot and dry for a

wild fire to start. When there has been no rain and

it has been very hot all the branches and twigs on

the ground are very dry. This is called a drought.

They can be started through natural causes such as

a lightning strike or in very rare cases a volcano

erupting. 4 out of every 5 wild fires are started by

people. Sometimes it is an accident, for example

people leaving a small fire burning or throwing a

cigarette away.

The dry twigs and branches on the forest floor provide

fuel for the fire. Winds can fan the fire and make it

spread quicker by pushing embers into part of the

forest that wasn’t burning yet.

HOW CAN THEY BE STOPPED?

One of the first things firemen do is to dig a gap

between the fire and parts of the forest that are not on

fire. They remove all of the trees and bushes in this

gap. Helicopters pick up water from lakes and drop it

on the fire. They also spray a coating of chemicals on

the trees that aren’t on fire. This stops the fire from

spreading.

Amazon forest fire covering half of Brazil.

Wildfire caused by lightning in California.

16

HOW CAN WILDFIRES BE BENEFICIAL?

Still, wildfires are essential to the continued survival of some plant species and can help keep ecosystems

healthy;

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17

Moving snow—AVALANCHES

A snow avalanche begins when an unstable mass

of snow breaks away from a slope. The snow picks

up speed as it moves downhill, producing a river of

snow and a cloud of icy particles that rises high into

the air. The moving mass picks up even more snow

as it rushes downhill. A large, fully developed

avalanche can weigh as much as a million tons. It

can travel faster than 320 km/hr.

During an avalanche, a mass of snow, rock, ice, soil,

and other material slides swiftly down a

mountainside. Avalanches of rocks or soil are often

called landslides. Snowslides, the most common

kind of avalanche, can sweep downhill faster than

the fastest skier.

EFFECTS OF AVALANCHES

An avalanche is able to obstruct anything in its path.

Roads and railways can be blocked. Power supplies

can be cut off. A powerful avalanche can even

destroy buildings and

people can also be

killed. 90 percent of

people who die in

avalanches trigger

them themselves.

People usually die

from a lack of oxygen

when buried in snow,

rather than from

getting too cold.

WHAT CAUSES AVALCHES?

______________________________________

______________________________________

______________________________________

______________________________________

______________________________________

______________________________________

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_ Skiers surprised in off-piste avalanche .

18

PREDICTING AN AVALANCHE

People try to predict when avalanches are going to

occur. The Alps has an 'avalanche season' between

January and March when most avalanches happen.

Where avalanches are going to occur is hard to

predict. Historical data, weather information and

information about the actual snow on the

mountainside is collected together to try and

forecast the likelihood of an avalanche.

Explosions

Avalanches can be started deliberately in order to

prevent the snow building up. This is one of the

most important ways of preventing avalanches.

Communicating the risk of an avalanche

Signs of the risk of avalanches can be displayed in

villages and also by the ski lifts. In the Alps the risk

is assessed on a five-point scale. Areas can be

sealed off which are considered too dangerous to

ski on. Early warning systems are also used.

Land-use zoning

Land can be grouped into red, yellow and green

areas. The red areas are considered too dangerous to

be built on. The orange areas can be built on with

restrictions, such as reinforcing buildings. Roads

and railways can be protected by tunnels over them

in the areas where an avalanche path is likely to

travel.

Snow fences and barriers

These can be used to divert and break up the path of

the avalanche.

Reforestation

Trees can be planted, increasing stability of the

slope and helping to reduce the damage further

down the valley.

Avalanche hazard sign .

19

CASE STUDY— Galtür avalanche Galtür is a popular ski resort in Austria.

Avalanches happen most years, but don't usually

reach the village of Galtür. On 23 February 1999,

an avalanche raced down the mountain.

CAUSES

The Galtür avalanche was a powder avalanche- due

to a period of heavy snowfall brought on by a

series of low pressure weather systems. Eventually,

the older layers of snow could not support the mass

of new snow, and a 50 feet high wall of snow was

formed, travelling at 200 kilometres per hour.

AFTERMATH

It travelled at 200 miles per hour, taking 50

seconds to reach the village.

31 people died, 26 of whom were tourists and 5

were locals. Rescuers saved 26 people in the

following 24 hours.

People in Galtür were stranded as roads were

blocked. 16 buildings were destroyed or

severely damaged.

Ski resorts were closed in the region, costing

the industry £5 million for each day they were

closed.

RESPONSE

Austria had devised a new zoning system, with red

being an area where construction of any type is

prohibited, and yellow, where certain safety measures

are put in place. Galtur was in the yellow zone. As a

result of the avalanche, Austria has invested in the

creation of steel fences near the area to break up the

impact of the avalanche, along with trees- deforestation

was one of the possible causes of the avalanche. A 300

metre long avalanche dam protects the village, and the

zoning of at risk areas has been made stricter. More

avalanche resistant buildings have been created.

Devastating disaster.

Galtur Avalanche search for missing persons.

A snow mass from the avalanche penetrated the interior of a house.

20

It’s raining mud!—MUDSLIDES

A mudslide, also called a debris flow, is a type of

fast-moving landslide that follows a channel, such as

a river. A landslide, in turn, is simply when rock,

earth, or other debris moves down a slope.

Mudslides occur after water rapidly saturates the

ground on a slope, such as during a heavy rainfall.

This happens when the pull of gravity is strong

enough to bring down material that is made fluid

enough by water.

Mudslides are also often triggered by earthquakes or

by disturbances in hillsides caused by fires or human

activity.

In the United States, mudslides and landslides result

in an average of 25 to 50 deaths a year, according to

the Centers for Disease Control and Prevention.

HOW ARE MUDSLIDES PREVENTED?

Strategies to decrease the risk of mudslides include:

draining water off hillsides

armouring the bases of hills so they are not

undercut by rivers.

engineers put large rocks, at the base of a hill to try

to anchor the slope and prevent it from coming

loose.

It is recommended that people exercise caution around

steep slopes during rainfall. Immediate signs of a

pending slide include tilting trees and sudden increases

or decreases in rivers.

Deadly Colombia landslide engulfs highway near Medellin .

21

Vargas tragedy is one of the worst disaster that

struck the Venezuelan country's Vargas state on 15

December 1999. It was a result of heavy downpour

of rain, flash floods and mudslides that followed

on 14-16 December 1999 . This disaster led to an

complete collapse of the infrastructure of the state of

Vargas.

Many towns were swept away to the ocean due to

the floods. Whole towns like Cerro Grande and

Carmen de Uria completely disappeared. As much

as 10% of the population of Vargas perished during

this event. The coastal area of Vargas has long been

subject to mudslides and flooding: geologically

similar catastrophes occurred with regularity. The

most recent major flood was in 1951, however that

event did not cause as much damage.

In a 52-hour span during 14, 15 and 16 December

1999, 91.1 cm of rain (approximately one year's total

rainfall for the region) was measured on the north-

central coast of Venezuela. Even so, the coast

received much less rain than some regions upstream.

The disaster caused estimated damages of USD $1.79

to $3.5 billion. The death toll was considered to be

between 10,000 and 30,000—the exact number of

casualties is difficult to determine as there was no

reliable census data, especially about shanty towns and

small communities that were completely wiped out;

moreover, only some 1,000 bodies were recovered,

with the rest swept to sea by the mud or buried in the

landslides. More than 8,000 homes and 700 apartment

buildings were destroyed in Vargas displacing up to

75,000 people.

CASE STUDY— Vargas tragedy

A section of Los Corales, one of the neighbourhoods in the Vargas state which suffered the heaviest destruction

Remains after the mudslide.

Shanty towns hit hardest by Venezuelan Floods / Shacks, people on steep slopes

just swept away.

22

Glossary avalanche a mass of snow, ice, and rocks falling rapidly down a mountainside.

climate change a change in global or regional climate patterns.

cyclone a system of winds rotating inwards to an area of low pressure.

drought a long period of abnormally low rainfall, leading to a shortage of water.

flash floods a sudden floods, typically due to heavy rain.

landslide a collapse of a mass of earth or rock from a mountain or cliff.

levees a ridge of sediment deposited naturally alongside a river by overflowing

water.

mudslides a mass of mud and other earthy material that is falling or has fallen down a

hillside or other slope.

natural hazard a natural phenomenon that might have a negative effect on humans or the

environment.

tropical storm very intense low-pressure wind system, forming over tropical oceans and

with winds of hurricane force.

wildfire a large destructive fire that spreads quickly over woodland or bush.