volcanoes · web viewvolcanoes form when hot material from below rises and leaks into the crust....

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.

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Figure 1: The Main Features of a Volcano

SM SUFRI BOLKIAH TUTONG

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.

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Figure 2: Distribution of the World’s Major Volcanoes


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.

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 3: Major Tectonic Plates of the World


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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

Figure 7: Activities at the Constructive 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.

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.

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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.

Shield Volcano

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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.


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.

Acid Cone 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.

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


Composite Volcanoes

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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 materialPyroclastic materials are the name given to particles produced in volcanic eruptions. E.g. ash and dust.

Fertile SoilThe 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. Tourist attractionThe 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.

Geo-thermal powerThe 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).

Rich in mineralsVolcanic 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.

POSITIVE IMPACT

Many lives can be lost as a result of volcanic eruption.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.Lava flows and lahars can destroy settlements, clear areas of woodland and agriculture leading to a great loss of property.Human and natural landscapes can be destroyed and changed forever. Fire hazardsPoisonous gases are emitted.There may be flood hazards.Earthquakes occur.Tsunamis (huge waves) may be caused.

NEGATIVE IMPACT

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Strategy 1: Removing the ThreatObviously, 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 FutureProtecting 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 PreparednessWhen 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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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.


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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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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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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.

Impact of volcanic eruption:


Social Impact

• Holiday villas damaged • Towns and villages

destroyed e.g. Catania• People died

Environmental Impact

• Vegetation destroyed • Animals killed • Habitats destroyed

Economic Impact

• 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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Responses after the volcanic eruption:


Immediate 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.

Long Term Response

• 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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Did you know?

The word volcano comes from the name of the Roman god of fire.

Did you know?

Kilauea on Hawaii is the world’s most active volcano-it has been erupting since 1983.

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?

Ash blown high into the atmosphere caused colourful sunsets in Europe for several months after the Mount St Helens eruption.

Did you know?

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?

The May 18,1980 Mt St Helens eruption was the most economically destructive volcanic event in U.S. history.

Did you know?

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?

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.

Did you know?

Most of Mt St Helens is younger than 3,000 years old (younger than the pyramids of Egypt).

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/volcano-profile/

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.


volcanoes · web viewvolcanoes form when hot material from below rises and leaks into the crust....

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