VOLCANOES
 A volcano is a conical hill or mountain
formed by material from the mantle being
forced through an opening or vent in the
Earth's crust.
 It is an opening of the earth’s crust from
which materials such as magma and gases
are ejected.
Figure 1: The Main Features of a Volcano
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Volcanoes form when hot material from below rises and leaks into the
crust. This hot material, called magma, comes either from the melted
subducted crustal material, which is light and buoyant after melting, or it
may come from deeper in the interior of a planet and is light and buoyant
because it is very hot.
Magma, rising from lower reaches, gathers in a reservoir, in a weak
portion of the overlying rock called the magma chamber. Eventually, but
not always, the magma erupts onto the surface.
Figure 2: Distribution of the World’s Major Volcanoes
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As seen in Figure 2, many of the world's active volcanoes are located
around the edges of the Pacific Ocean; the West Coast of the Americas;
the East Coast of Siberia, Japan, the Philippines, and Indonesia; and in
island chains from New Guinea to New Zealand--the so-called "Ring of
Fire" (Figure 4). Recently, active volcanoes were also found in Iceland, the
Kenya Rift Valley in Eastern Africa, Italy, and Hawaii.
Figure 3: Major Tectonic Plates of the World
 FACT 1: Volcanoes are usually found along or near the plate boundaries
(Figure 2).
 FACT 2: They occur where molten rock (magma) comes to the surface of
the earth. The magma rises to the surface through cracks in the crust called
vents.
 FACT 3: Volcanoes are formed along two types of plate boundary:
destructive and constructive.
 FACT 4: Volcanoes are concentrated in a belt around the Pacific Ocean.
The belt of volcanoes is called the Pacific Ring of Fire (See Figure 4 & 5).
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Figure 4: The Pacific Ring of Fire
Figure 5: Distribution of Active Volcanoes along the Pacific Ring of Fire
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Figure 6: Activities at the Destructive Plate Boundary
 FACT 5: As seen in Figure 4 and 5 volcanoes mainly occur along
destructive plate boundaries (where plates move towards each other). Along
the boundaries (refer to Figure 6), convectional currents of magma in the
upper mantle converge and sink, causing a continental plate and an oceanic
plate to collide. Along the subduction zone where the plates meet, magma is
produced by the melting of the subducted plate in the mantle. This magma
rises to the surface of the Earth forming volcanoes.
Figure 7: Activities at the Constructive Plate Boundary
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 FACT 6: Volcanoes can also occur along constructive plate boundaries
(where plates move away from each other). Along this type of boundary
(refer to Figure 7), the rising convectional currents of magma in the upper
mantle will drag the crust apart as they diverge (move away from each
other). This leads to the creation of a fissure/crack/gap. Magma is
injected into this fissure on the mid-oceanic ridges and this will lead to the
formation of volcanoes.
For example: Along the Mid-Atlantic Ridge, magma rises through the long
fissures created by plates moving apart. The lava cools and solidifies on
the ocean floor to form submarine volcanoes. If the volcanoes are high
enough to reach above the sea level, they form volcanic islands e.g.
Iceland.
 FACT 7: Volcanoes may also form at the centre of a plate and are called ‘hot spot’
volcanoes. Examples of volcanoes formed this way are the volcanoes on the
Hawaiian Islands in the Pacific Ocean and also in Africa. Hot spot is also known as
plume. A plume is an area of localized swelling and cracking of the earth’s crust due
to an upward welling of magma.
 FACT 8: Why do volcanic eruptions occur?
Rocks that lie beneath the earth’s crust are under great pressure and have very high
temperatures that keep them in a semi-liquid state known as magma. Crustal
movements create lines of weaknesses or fractures in the earth’s crust.
When pressure beneath the earth’s crust is released, the molten magma forces its
way out onto the surface of the earth as lava through the fractures and volcanic
eruptions occur.
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VOLCANOES
Important FACTS to know:
 There are THREE types of volcanoes:
1. Shield Volcano
2. Acid Cone Volcano
3. Composite Volcano
 Each type of volcano is made up of different types of lava. There are two types
of lava:
1. Basic Lava
2. Acidic Lava
 Basic lava is thin. It cools and solidifies slowly and therefore it is able to
spread or flow over a wide area. As a result, it forms a cone with gentle slopes.
 Acidic lava is thick. It cools and solidifies quickly and therefore it is unable to
spread over a wide area. Lava may even cool and solidify as it flows up the
vent. As a result, it forms a cone with steep slopes.
Shield Volcano
 When lava is runny and thin it can flow a long way before cooling and solidifying,
this causes shield volcanoes to have gentle slopes and wide bases built almost
entirely of low viscosity basaltic lava flows.
 Shield volcanoes are the largest of the three types of volcanoes.
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 Frequent eruptions but usually quiet and gentle with large quantities of fluid basic
lava.
 Example: Mount Kilauea and Mount Mouna Loa in Hawaii (USA), Galapagos
Islands, Snake River Plain in Idaho, USA.
Acid Cone Volcanoes
 When lava is thick and acidic it doesn’t flow far before cooling and solidifying, this
causes cone volcanoes (aka acid cone volcanoes) to have steep sides.
 Viscous acidic lava flows from a central vent, cools and solidifies quickly. Lava
may even cool and solidify as it flows up the vent.
 When lava solidifies and blocks the vent, massive violent explosion may occur as
pressure and gases are being built up inside the volcano. The entire top may be
blown off.
 Examples: Mount Pelee on Martinique (an island in the Caribbean).
Mount Stromboli, Italy
Mount Mageik, Alaska
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Composite Volcanoes

A volcano made up of viscous lava, ash and cinder which has secondary cones
on the sides. This is because the lava often escapes through the sides, creating
separate cones. The volcano has steep slope near the summit, but gentle slope
near the base.

Alternate eruptions of viscous acidic lava, ash and cinder. Therefore creates
violent explosions. Lava may escape through the sides of the cone.

Example: Mount St Helens in Alaska (USA), Mount Shasta in California,
Mount Fuji in Japan and Mount Mayon in the Philippines.
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The severity of volcanic eruptions is dependent on several factors such as how violent
the eruption is, the viscosity of the lava and the type of volcanic materials released in
the event of a volcanic eruption.
 How violent the volcanic eruption is.
This is determined by the composition and temperature of the magma
and the dissolved gases in the magma.
 The viscosity of the lava.
Viscosity is the measure of the material’s resistance to flow.
 Volcanic material
Pyroclastic materials are the name given to particles produced in
volcanic eruptions. E.g. ash and dust.
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POSITIVE IMPACT
1. Fertile Soil
The lava and ash deposited during an eruption breaks down to provide valuable
nutrients for the soil. This creates very fertile soil which is good for agriculture.
E.g. in Java and Deccan Plateau in India.
1. Tourist attraction
The dramatic scenery created by the volcanic eruptions attracts tourists. This
brings income to the area. E.g. Mount Fuji in Japan.
Spas with medicinal springs are health resort.
Famous geyser e.g. Old Faithful in Yellow stone National Park.
2. Geo-thermal power
The high level of heat and activity inside the Earth, close to a volcano, can
provide opportunities for generating geothermal energy which could be used to
generate electricity e.g. in New Zealand (North Island).
3. Rich in minerals
Volcanic areas are also rich in mineral such as sulphur, copper and tin.
Mining can be carried out in these area.
E.g. diamonds of Kimberly in South Africa.
NEGATIVE IMPACT
1. Many lives can be lost as a result of volcanic eruption.
2. If the ash and mud from the volcanic eruption mix with rain water or melting
snow, fast moving mudflows are created. These flows are called lahars.
3. Lava flows and lahars can destroy settlements, clear areas of woodland and
agriculture leading to a great loss of property.
4. Human and natural landscapes can be destroyed and changed forever.
5. Fire hazards
6. Poisonous gases are emitted.
7. There may be flood hazards.
8. Earthquakes occur.
9. Tsunamis (huge waves) may be caused.
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There are four general approaches to coping with volcanic hazards. (1) We can try to
keep the hazard from occurring which is often an impossible task. (2) We can try to alter
its path or reduce its impact on existing development. (3) We can take steps to protect
future development. (4) We can also do our best to have disaster response plans in
place before they are needed.
Strategy 1: Removing the Threat
Obviously, there is no way to stop an eruption. We can, however, attempt
to reduce the eruption's effects by reinforcing structures (for example,
strengthening roofs to support the weight of tephra deposits) or by building
protective works (such as walls to deflect lava flows away from developed
areas). Such efforts can be and have been successful, but are of limited
use in a large-scale eruption.
Strategy 2: Planning for the Future
Protecting future development from volcanic hazards is a simpler task.
Before building, we should evaluate the risk. If it seems too great, a safer
location should be found. This type of planning is very effective, but all too
often, people are drawn to the lush, rolling terrain of a quiet volcano.
Strategy 3: Disaster Preparedness
When a volcano comes to life, a few weeks may not be enough time to
avert a tragedy. Planning is the key to saving lives. Well before the warning
signs occur, people must be educated about volcanic hazards. Evacuation
plans must be in place. Communication between scientists, officials, the
media, and the general public should be outlined and practiced. Emergency
measures must be thought out and agreed upon.
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VOLCANOES
Mount Merapi is located in Central Java, Indonesia
The 2010 eruptions of Mount Merapi began in late October 2010 (started erupting on
25th October). It began with an increasingly violent series of eruptions that continued
into November. Seismic activity around the volcano has increased from mid-September
onwards, culminating in repeated outbursts of lava and ashes. Large eruption columns
formed, causing numerous pyroclastic flows down the heavily populated slopes of the
volcano. Merapi's eruption was said by authorities to be the largest since the 1870s.
Over 350,000 people were evacuated from the affected area. However, many remained
behind or returned to their homes while the eruptions were continuing. 353 people were
killed during the eruptions, many as a result of pyroclastic flows. The ash plumes from
the volcano also caused major disruption to aviation across Java.
The mountain continued to erupt until 30 November 2010. On 3 December 2010 the
eruptive activity had subsided.
Case study (LEDC): Mount Merapi
 Location of case study: Central Java, Indonesia
 When did the volcano erupt?: Began on 25th October, 2010
 Impact of volcanic eruption: 350, 000 people were evacuated, 353 people killed,
ash plumes caused flights to be delayed, and houses were destroyed.
 By 1st November, 2010, the Crisis Center MOH reported 42 people died and 103
people were admitted to several health facilities with respiratory difficulties and
burn injuries. Up to 70,143 people were reported to have been displaced. Health
problems amongst the evacuees included acute respiratory infection, eye
irritation, cephalgia, and hypertension.
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 Land transportation beyond the 10 kilometres (6.2 mi) restricted area was not
disrupted but air transportation was affected for flights from and to Yogyakarta
and Solo.
 Heavy rain during the night of 3–4 November triggered lahars with mixtures of
water and rock debris cascading down the Kuning, Gendol, Woro, Boyong,
Krasak and Opak rivers on the slopes of the volcano. A bridge was destroyed
and riverbanks damaged.
 Borobudur, an 8th century Buddhist temple and one of the world's largest
Buddhist monuments, was heavily affected by the eruption in early November
2010. Volcanic ash from Mount Merapi fell on the temple complex, which is
approximately 28 kilometres (17 mi) west-southwest of the crater. A layer of ash
up to 2.5 centimetres fell on the temple statues during the eruption of 3–5
November, also killing nearby vegetation, with experts fearing that the acidic ash
might damage the historic site. The temple complex was closed from 5
November to the 9th to clean up the ashfall.
 Borobudur was again "temporarily closed for tourists" from the morning of 10
November due to the continuing fall of volcanic ash
 Strategies to reduce impact of volcanic eruption: Constant monitoring of volcanic
areas, provide efficient rescue and evacuation plans through training and education,
and create exclusion zones from high risk areas.
 Staff from the Center for Volcanology and Geological Hazard Mitigation at Merapi
continuously monitored Mount Merapi since the eruption began.
 The Indonesian government and the Indonesian Red Cross and Red Crescent
(PMI) fielded up to 398 volunteers from branches in the provinces of Central
Java, and Yogyakarta. These volunteers assisted in disseminating information to
communities to warn of Merapi’s level IV volcanic activity. PMI also provided
meals for 1,000 displaced people in the Dompol camp.
 The Geological Agency provided several recommendations including that there
would be no community activities in the disaster prone areas and proclaimed an
ongoing exclusion zone of 2.5 kilometres (1.6 mi) radius.
 The military mobilized a brigade to build makeshift hospitals and public kitchens
to serve the growing number of displaced.
 Refugee camps were set up to help the displaced villagers.
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VOLCANOES
The 2010 eruptions of Eyjafjallajökull were volcanic events at Eyjafjöll in
Iceland which, although relatively small for volcanic eruptions, caused
enormous disruption to air travel across western and northern Europe over an
initial period of six days in April 2010. Additional localized disruption continued
into May 2010. The eruption was declared officially over in October 2010, when
snow on the glacier did not melt.
Between 14 and 20 April, ash covered large areas of northern Europe when the
volcano erupted. About 20 countries closed their airspace (a condition known
as ATC Zero) and it affected hundreds of thousands of travellers. The
European flights avoided about 344,109 tonnes of carbon dioxide emissions
per day, while the volcano emitted about 150 000 tonnes of carbon dioxide per
day.
About 500 farmers and their families from the areas of Fljótshlíð, Eyjafjöll, and
Landeyjar were evacuated overnight (including a group of 30 schoolchildren
and their 3 teachers from Caistor Grammar School in England), and flights to
and from Reykjavík and Keflavík International Airport were postponed.
The police closed the road to Þórsmörk, and the four-wheel-drive trail from
Skógar village to the Fimmvörðuháls mountain pass, but these roads and trails
were reopened on 29 March, though only for suitable four-wheel drives. When
the second fissure appeared, the road was closed again because of the danger
of flash floods, which could have developed if the fissure had opened near big
ice caps or other snow reservoirs, but the road was again opened at around
noon on 1 April.
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VOLCANOES
Case study (MEDC): Mount Etna
 Location of case study: Sicily, Italy (located on a destructive plate boundary
between the Eurasian & African plate).
 When did the volcano erupt?: July, 2001
 Why the eruption happened?: The Eurasian plate is subducted under the African
plate. Friction causes the crust to melt and this force its way up into the magma
chamber. Pressure builds up in the magma chamber and eventually is released as an
explosion. This causes gas and steam to escape, volcanic bombs, lava and pyroclastic
flows.
Social Impact
 Impact of volcanic eruption:
• Holiday villas damaged
Environmental Impact
• Towns and villages
destroyed e.g. Catania
• Vegetation destroyed
•
People died
• Animals killed
•
Habitats destroyed
Economic Impact
•
•
•
•
•
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Orange groves & vineyards wiped out in Zafferana.
Roads destroyed so hard to access area
Ski areas ruined
Farms destroyed & covered in ash
Airport forced to close due to ash on the runway.
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VOLCANOES
 Responses after the volcanic eruption:
Immediate Response
Long Term Response
•
•
•
•
•
•
•
•
•
•
Panic
People moved out of the area.
Villagers in Nicolosi prayed to
reduce impact of eruption.
US army helicopters drop 2 tonne
concrete blocks to stop lava flow
Earth dams are built to re-direct lava
flow
500kg mines exploded to divert lava.
Italian government gave £5.6m of
aid.
Decision to shut airport on 29th July.
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•
•
•
Rebuilding damaged buildings
Scientists improve monitoring of
volcano.
More planning of emergency
services & evacuation plan.
Use tourism to generate money &
income from the area.
Italian government gave tax breaks
to help villagers get through the
crisis.
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VOLCANOES
Did you know?
Did you know?
Did you know?
The word volcano
comes from the
name of the
Roman god of
fire.
Kilauea on Hawaii is the
world’s most active
volcano-it has been
erupting since 1983.
Ash blown high into the
atmosphere caused colourful
sunsets in Europe for several
months after the Mount St
Helens eruption.
Did you know?
Did you know?
Did you know?
The May 18,1980 Mt
St Helens eruption
was the most
economically
destructive volcanic
event in U.S. history.
Most of Mt St Helens is younger
than 3,000 years old (younger than
the pyramids of Egypt).
About 90% of the world’s
1900 active volcanoes are in
the Ring of Fire, a band of
volcanoes circling the Pacific
Ocean.
Did you know?
Did you know?
Mt Pinatubo’s crater lake had a
pH of 1.9 in 1992-capable of
causing burns to human skin!
Did you know?
The volcanic ash cloud from
Mt St Helens eruption in
1980 drifted east across the
United States in 3 days and
encircled Earth in 15 days.
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If the volcano on La Palma in the
Canaries explodes, a 500-metre-high
mega tsunami could engulf low-lying
parts of the UK.
Did you know?
Early forecasts by scientists on Mt
Pinatubo’s eruption in June 1991
saved at least 5,000 lives and
prevented property losses of at
least $250 million.
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RESOURCES
Useful Websites on Volcanoes:
http://www.geography.learnontheinternet.co.uk/
http://www.mapsofworld.com/major-volcanoes.htm
http://news.bbc.co.uk/2/hi/136248.stm
http://www.enchantedlearning.com/subjects/volcano/ringoffire/
http://pubs.usgs.gov/gip/volc/fig34.html
http:// volcanoes.usgs.gov
http:// www.pubs.usgs.gov/gip/103/
http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/volcanoes_rev1.
shtml
http://www.geography-site.co.uk/pages/physical.html
http://geography.about.com/cs/earthquakes/a/ringoffire.htm
http://environment.nationalgeographic.com/environment/natural-disasters/volcanoprofile/
http://www.bennett.karoo.net/topics/volcanoes.html
Books on Volcanoes:
Cambers, G. & Sibley, S. (2010). Cambridge IGCSE Geography. Cambridge: University
Press.
Hancock, J. & Bilham-Boult, A. (2007). Revise GCSE: Complete Study & Revision
Guide. London: Letts & Lonsdale.
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