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Natural Hazards
1. (a & b) Natural Hazards: a general
survey
2. Tectonic plate boundaries
3. Earthquakes
4. (a & b) Why earthquakes have
different impacts
5. (a & b) Volcanic activity
6. (a & b) The costs and benefits of
volcanoes
7. (a & b) Climatic hazards – high winds
8. Cyclones and their effect on people
9. (a & b) Drought and desertification
10. (a & b) The ecosystem
11. Tropical rainforests
12. Impact of people on ecosystems
13. (a & b) Tropical rainforest clearance
14. Air pollution
15. Acid rain causes and effects
16. Global warming and the greenhouse
effect
17. Causes of land and water pollution
18. Sustainable use and development
of resources
1a. Natural Hazards: a general
survey
These are short-term, natural events that pose a threat to life and property
Causes
• Plate movements – these are the cause of earthquakes and volcanic activity. The
events themselves are unpredictable, especially earthquakes. The main areas where
plate movements are possible are known, but no-one can predict exactly when and
where an earthquake will strike, nor how strong it will be.
• Climatic extremes – these include high winds, floods and drought. There is more
chance of forecasting these, but it is not always possible to be accurate. Hurricanes
are tracked by satellites, but can change course at any time.
• Effects
• Primary (direct) effects – people are killed, buildings are destroyed and normal life is
disrupted
• Secondary effects – people experience shortages of safe water and food, disease
spreads and there is homelessness. These effects can be felt for weeks, months or
even years.
1b. Natural Hazards: a general
survey
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Floods – some warning but many
people live on floodplains
Earthquakes – happen without warning
Storms – Cyclones in the Tropics are
the worst killers
Volcanoes – often warning signs of an
eruption
Droughts and famine - mainly affect
the poor in African countries
Poor people are hit harder by hazards.
They cannot afford to prepare for them
and they do not have the resources to
recover quickly after the event.
Loss of life from different
natural hazards
Volcanoes
2%
Floods
19%
Storms
45%
Earthquakes
34%
2. Tectonic plate boundaries
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Tectonic activity is the movement of the large rock plates of the Earth’s crust. Energy
to move the plates comes from the Earth’s interior. Activity strong enough to cause
earthquakes and volcanoes is concentrated along plate boundaries. There are three
types of activity:Constructive or Divergent – two plates move away from each other. The gap where
they diverge is filled with molten magma from the Earth’s interior. The magma
spreads outwards and forms new crust. Landforms are basic lava or shield
volcanoes and a mid oceanic ridge.
Destructive or Convergent – two rock plates move towards each other and collide.
Sediments are compressed and folded up. One plate is destroyed as it sinks below
the other into the subduction zone. The crust melts and magma rises to the surface.
Landforms are acid lava or composite volcanoes and fold mountains.
Conservative – two rock plates move past each other. There are no characteristic
landforms; there is no loss or gain of land, but many earthquakes occur.
Plate boundaries are where most of the activity takes place.
3. Earthquakes
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An earthquake is the shaking of the ground. It is caused by shock waves from the
sudden movement along a plate boundary. Moving plates get stuck together,
especially along destructive and conservative boundaries. Pressure builds up until
eventually the friction between them is overcome and the plates jerk past one
another. The focus is the point underground where the earthquake occurs. Above it,
on the surface, is the epicentre. This is where the surface shaking is greatest. Its
magnitude is recorded on a seismograph and given a value between 1 and 10 on the
Richter scale.
Immediate effects include deaths and injuries, collapsed buildings and bridges, and
destruction of roads and power lines.
Short- term effects include trapped people needing to be rescued, injured people
needing treatment, shortages of medical supplies, food, clean water and shelter and
spread of disease
Long-term effects include homeless people living in tents and camps, lack of power
and high cost of rebuilding buildings, bridges,roads etc.
4a. Why earthquakes have different
impacts
“The stronger the earthquake, the greater
the impact “ is partly true. Other
factors include:
• The density of the population and the
number of people living close to the
epicentre
• The quality of construction of the
buildings
• How well prepared the people and
emergency services are
Two earthquakes of the same strength can
have very different impacts:
California, 22 December 2003
• Magnitude 6.5
A clock tower was toppled, killing three
people
Iran, 26 December 2003
• Magnitude 6.5
• A large part of the city of Bam was
flattened, killing an estimated 30,000
people
Why was the death toll in Iran was so
high?
• Poor building methods had been used
eg bricks were held together by mud
• Building regulations were inadequate
or ignored
• Rapid population growth had led to
cheap homes being built quickly and
without supervision
4b. Why earthquakes have
different impacts
Strategies to reduce the loss of life in an earthquake
Since earthquakes cannot be predicted, the only way to reduce loss of life is to make
preparations in advance.
How to make buildings earthquake resistant
• Use dampening and bracing systems to help absorb shocks
• Use steel frames
• Make foundation piles out of alternate layers of steel and rubber to make the
skyscraper flexible in an earthquake
How to prepare people for an earthquake
• Prepare leaflets with advice, such as: stand under a door frame; move to an open
space; keep emergency supplies of food and drink
• Hold regular emergency drills
• Train a team of rescuers within the emergency services
It is easier for rich countries to adopt these strategies than for poor countries because
they have the money, resources and trained people.
5a.Volcanic activity
A volcano is a cone shaped mountain formed by surface eruptions of magma from the
inside of the Earth. Volcanoes form along both constructive and destructive plate
boundaries, but the types of volcano formed are different.
Formation of volcanoes at constructive and destructive boundaries
Constructive
Destructive
Materials erupted Mainly lava
Lava bombs, ash, dust
Type of lava
Basic, runny, flows well
Acid, sticky and slow flowing
Eruptions
Frequent, rarely violent
Haphazard, can be violent
Shape of the cone Broad base and gentle sides Tall steep-sided, perfect cone
(shield volcano)
(composite cone)
Example
Mauna Loa in Hawaii
Mount Etna in Sicily
5b.Volcanic activity
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Formation of a composite volcano
At a destructive plate boundary one
plate is destroyed
Pressure and friction make rocks of
the crust melt
Magma rises through a pipe (vent) and
reaches the surface. It is forced out of
the crater as lava and other materials
to form a cone shaped mountain
More lava and ash build up around the
crater as a high steep cone
As with earthquakes, volcanic
eruptions are rare in areas away from
plate boundaries. There are more
active volcanoes in the Pacific Ring of
Fire, which includes Japan and
Indonesia, than anywhere else
6a.The costs and benefits of
volcanoes
About 500 million people live in volcanic
regions. What are the dangers for
people from active volcanoes?
Costs: negative effects of volcanoes
• Total destruction – buildings, roads,
farmland and everything else covered
by lava and ash
• Loss of life and injuries to people
working in the fields or caught
unawares
• Forced migration of people from the
affected area
• Global effects – dust clouds sent high
into the atmosphere, reducing
temperatures by blocking out sunlight
6b.The costs and benefits of
volcanoes
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Benefits: usefulness of volcanoes
Produce fertile soils (weathering of the
lava and ash gives some of the world’s
best cropland e.g. the plain around Mt.
Vesuvius
• Provide hot water for geothermal
power and heating buildings e.g.
Iceland and new Zealand
• Produce useful minerals e.g. Sulphur
• Provide great tourist attractions e.g. Mt
Vesuvius and Blue Lagoon in Iceland
(bathing in thermal baths)
Unlike earthquakes, volcanoes do have
advantages for human settlement.
Also there are often warnings that an
eruption may be about to take place,
so there are fewer deaths
7(a) Climatic hazards: high winds
In the UK gale force winds are linked to
depressions.
Damage includes trees uprooted, tiles
lifted off roofs and power lines brought
down. Travel by road, rail, ferry and air
is disrupted.
In the tropics cyclones have even lower
pressure, winds up to 200km per hr
cause devastation, especially in coastal
areas.
Formation of cyclones (hurricanes)
Hot sea surfaces above 27 degrees are
needed, found only in the tropics in late
summer. Hot, moist air rises in
convection currents, cumulonimbus
clouds form and heavy rain falls. Very
low pressure at the surface cause the
high winds
Areas affected
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Caribbean islands and costal areas
of central America and the USA are
worst affected by hurricanes.
Cyclones also found in Indian
Ocean and typhoons along east
coast of Asia
High winds are most dangerous in
coastal area. Moving inland, wind
speed is reduced by friction over
uneven land surfaces
7 (b) Hurricanes
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More than 80 degrees F = 27 degrees C
8 Cyclones and their effect on
people
Badly affected
Less affected
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Coastal areas – receive full force of
cyclone
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Inland areas – strength of cyclone
lost over land
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Densely populated urban areas
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Less densely populated rural areas
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Poor countries are less likely to
receive advance warnings and they
lack the resources needed to make
preparations
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Rich countries receive early
warnings through tv channels and
have shelters and emergency
procedures
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So in the Caribbean the islands
some islands are devastated whilst
those further away from the start of
the cyclone have longer to prepare
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Key case study – Hurricane Katrina
9a Drought and Desertification
Drought – periods of dry weather that
last longer than normal.
• Deserts are dry so don’t get
droughts!
• Lack of water means reduced crop
yields, lack of good grazing, lower
levels of water in rivers and
reservoirs.
• Land becomes overused – leads to
problems of soil erosion (loss of
fertile soil) and desertification
(spread of desert)
• When rains return water removes
even more soil.
• When drought strikes, people
overuse the land trying to survive.
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4 main human causes of
desertification – over-cultivation,
overgrazing, over-collecting of
wood for fuel and over-population
Many people migrating to areas
with more food – may be in same
country or may be international
migration.
Solutions –
small scale – use stones along the
contours of slopes to reduce soil
erosion
Keep fewer animals
Long term – birth control to reduce
rate of increase of population
Reduce impact of global warming
9b Sahel
Sahel, region in Africa to south of
Sahara Desert
• Eg Mali, Burkino Faso, Ethiopia
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Populations are increasing fast in
LEDCs of Africa; there are no food
surpluses even in wet years
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Global warming may be making the
climate of the area even more dry
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Ethiopia has been affected by
drought repeatedly by drought
during the last 20 years.
Problem would have been far worse
without food aid
10 (a) The ecosystem
Natural systems where climate and
soils (physical) are linked with
vegetation and animals (living)
Climate affects the type of vegetation
• On the equator – hot and wet all
year – tropical rainforests grow
• Where winters are too cold for tree
growth (UK) there is deciduous
woodland
Natural vegetation affects climate,
soils and animal life
• Trees intercept rain and return
water to the atmosphere, providing
water for more rain
• Dead leaves release nutrients back
into the soil
• Leaves and fruit provide food for
animals
10(b) Changes to ecosystems
Change to one component has knock
on effects
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Climate – there being less rainfall.
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Soils – they contain fewer nutrients
and are less fertile.
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Animal life – there is less food to
sustain it.
Natural ecosystems are under ever–
increasing pressures from growing
numbers of people. Human begins are
increasing their influence out of
proportion to that of all of other
animals in the system.
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11 Tropical rainforests
Characteristics
• Emergents – 40m+ above the forest
top
• Canopy – continuous layer of tall
trees 30 – 40m
• Discontinuous under canopy 10 –
30 m high
• Forest floor vegetation – shrubs
and ferns
Greatest biodiversity because of huge
number of plants and animals
Climate conditions are perfect for plant
growth – hot (27C) and wet (2000mm a
year). Competition for available light.
12 Impact of people on
ecosystems
Main reasons for greater impact
• Improved technology – machines
clear huge area quickly
• More people
• Areas are cleared for
• Farming
• Land for settlements
• Mining
• Roads
• Economic uses – building materials
fuel
Once vegetation is cleared, soil
structure is changed, even if people
abandon land same sorts of plants
unlikely to grow back
Rivers become full of eroded soil
13(a) Tropical rainforest clearance
Reasons for clearance
Economic
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To exploit resources – hardwood
timbers, iron ore, bauxite (for
aluminium), gold which are used for
exports to earn money and reduce
debt or for home industries to use
To build HEP stations to supply
cheap power to the cities
Social
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To open up new areas for
settlement to reduce pressure on
coastal urban areas
To give landless peasants the
chance to own land
Political
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Government wants more of the
country’s resources to be used
Opening up of new land diverts
people’s attention away from other
problems
What has been done in Brazil?
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Roads – Transamazonian Highway
Mining – Carajas region
Logging – removal of valuable trees
eg mahogany
Land cleared for cattle ranches and
to grow soya beans (exported for
animal feed in MEDCs)
13(b) Tropical rainforest clearance
For deforestation
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Miners
Loggers
Road builders
Dam builders (for HEP)
Government wanting economic
development
Cattle ranchers
Against deforestation
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Local people practising shifting
cultivation
Local people collecting wild rubber
Environmentalists
14 Air Pollution
Pollution is contamination of the
natural environment, as a result of
human action. There are three main
types: Air pollution, Land pollution and
Water pollution.
• Traffic is a major source of gases,
unburnt hydrocarbon and smoke
particles. Under certain weather
conditions, these pollutants are not
readily dispersed, e.g. where there
is;
• No wind to blow them away
• High pressure with sinking air,
which stops them rising to the
atmosphere
• Dry weather without rainwater to
wash them away
15 Acid rain causes and effects
Causes
• Rainwater is made more acid by
sulphur dioxide and nitrogen oxides
formed when fossil fuels are burnt.
Coal-fired power stations, vehicle
exhausts and factories are
important sources
• Once in the atmosphere, they are
carried by prevailing winds to other
places. Some is deposited straight
onto the surface – dry deposition,
some is converted to acids – wet
deposition
Effects
• Trees lose their leaves
• Fish and plants cannot tolerate
more acidic water in lakes
• Farmers have to buy more fertiliser
• Stonework seriously effected on old
buildings
16 Global warming and greenhouse
effect
Global warming – the rise in average
world temperature in 1850, this was
14.0°C. In 2000, it was 14.8°C.
There are natural and human causes of
global warming.
Natural- the climate keeps changing:
the earth has been warming up for the
last 10 000 years, since the ice age.
Human- cutting down trees and
burning fossil fuels releases more
carbon dioxide into the atmosphere.
In the atmosphere greenhouse gases
eg carbon dioxide trap some of the heat
radiated from the earth’s surface.
This keeps the earth’s surface warmer
than it would otherwise be. As the
amount of carbon dioxide in the
atmosphere increases, more heat is
trapped. – Greenhouse effect
17 Causes of land and water
pollution
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Farming – animal wastes, fertilisers
and pesticides when overused.
Surplus nitrates and phosphates
find way into rivers, cause rapid
growth of algae. Other plant and
animal life stops as algae dies and
decomposition uses up oxygen –
eutrophication
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Industries and urban areas – raw
sewage, domestic waste, toxic
waste from industry (lead, mercury
and arsenic) radioactive waste from
nuclear power stations
18 Sustainable use and
development of resources
Needs of future generations have to be
considered as well as those of people
living today –
Development should be
sustainable
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Using renewable alternative energy
(HEP, wind…) helps to conserve
resources of non renewable fossil
fuels
Recycling and reusing non
renewables- using scrap iron not
new iron ore
Protecting ecosystems against
destruction – preserving
biodiversity- by using selective
logging and by replanting