natural hazards - #dlsgeo · 25/08/2005 · natural hazards are extreme natural events that can...
TRANSCRIPT
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.