Natural Hazards
Programme 2: Volcano

Aims

• To describe and explain the volcanic eruptions on the West Indian island of Montserrat
• To illustrate the effects and consequences of the eruptions
• To explore the relationship between the volcanic hazard and the effect on human activity
• To assess the economic impact of the disaster

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Outline

00.00–02.19 Introduction to the West Indian island of Montserrat, the Soufrière Hills volcano and opening titles
02.20–03.42 An explanation of the causes of the first eruption in April 1995
03.43–04.37 Dramatic footage of the erupting volcano and pyroclastic flows of lava at 600ºC and speeds of 120 km per hour
04.38–05.38 The initial impact of the volcanic eruption on the islanders – uncertainty and fear
05.39–06.24 In June 1997, a second huge eruption took place and another pyroclastic flow began
06.25–07.09 The impact of this second eruption on the landscape, buildings and people – includes individual stories
07.10–07.52 By 2000 the southern part of Montserrat was declared an exclusion zone and the population had to move to the north of the island or move abroad – 9,000 people chose to leave
07.53–08.57 Large numbers decided to stay and they began to rebuild their lives in the northern third of Montserrat constructing buildings, roads and producing locally grown food
08.58–11.12 In September 2002, the volcano erupted again – a 2,000 metre high cloud of ash, rock and hot gas and two pyroclastic flows – and in an area that had been considered safe. Scientists installed a drilling rig to drill into the mountain to try to find out the cause of this eruption and to predict future events
11.13–14.52 A further area of land was added to the exclusion zone and some people had to move home again – difficult decisions had to be made – includes individual stories
14.53–end Credits

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Curriculum Relevance

• Hazards created by tectonic activity and the effects and responses to volcanoes
• Characteristic features at tectonic plate boundaries and the effects of movement
• A case study of one active volcano and its management

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Background

What is a volcano?
A volcano is an opening in the earth's crust (called a vent) where molten rock called magma, ashes and steam are brought to the surface of the earth. Volcanoes are found in one of three phases of their life cycle – active, where frequent eruptions occur, dormant, where there is a long time between eruptions, and extinct, where no eruptions have been recorded. The Soufrière Hills volcano on Montserrat is an active volcano.

Why do we get volcanoes?
The earth's crust is like a broken eggshell and the individual pieces of the 'shell' are called plates. The plates though are gigantic slabs of the earth's crust. This is called The Theory of Plate Tectonics.

The boundaries between these plates are lines of weakness in the crust and the rocks are put under great pressure as the plates move against each other.

Where the plates are moving apart the boundary is called a constructive plate boundary and new crust is formed in the form of molten rock (magma). Where plates are pushing together one plate may be forced under another and the crust is destroyed. This is known as a destructive plate boundary. Sometimes plates just slide past each other and no crust is created or destroyed – called conservative plate boundaries.

The volcano on Montserrat occurs where one plate is sliding under another at a destructive plate boundary.

Can volcanic eruptions be predicted?
Scientists have tried for a long time to find a way to predict exactly when a volcano is going to erupt. To be able to do so would be a major breakthrough because many lives could be saved. Seismology, which is used to study earthquakes, records the sounds when rock cracks or breaks. In active volcanoes there are thousands of these cracks and breaks where magma and gas are forcing their way to the surface. Seismic activity is always present in active volcanoes. The major difficulty has been to interpret these seismic signals so that the precise moment of the eruption can be predicted.

Dr Bernard Chouet from the US Geological Survey undertook detailed research into seismograph readings from active volcanoes and he noticed a pattern that no other scientist had seen. He called this pattern a long period event and he recognised a sequence that was the same as 'resonance' in music. He used the comparison of resonance in organ pipes where the pressure of the air in the pipes vibrates and the sound that is heard is air vibrating (resonating) in the pipe as the pressure is released.

In science, resonance is the sound of a gas or a liquid under pressure but in a volcano that pressure continues to build up because the magma and gas have nowhere to go – the volcano is sealed. Chouet believed that the appearance of the long period events on the seismograph was the major signal that pressure was building in a volcano and it was about to erupt.

If Chouet's observations are proved to be consistent in determining future volcanic eruptions then a major discovery will have been made.

What were the effects of the volcanic eruption on Montserrat?
The Soufrière Hills volcano on Montserrat erupted in April 1995 after 350 years of non-activity. The eruption was of the most violent variety. The lava built up under enormous pressure until it collapsed under its own weight. It cracked and splintered before hurling itself downwards as a pyroclastic flow, one of the deadliest forces in nature. The flows reached temperatures of 600º Celsius and speeds of 120 kilometres an hour.

During the eruptions the people had to decide whether to stay and take a chance, or to give up and leave. About two thousand people of the island's population of 13,000 left the island.

In June 1997 another eruption took place and huge chunks of the lava dome gave way and piled down in another pyroclastic flow. It emptied into the ocean, well beyond the coastline and added another square kilometre of new land to the island. Nineteen people were killed, most of them burnt to death in the flows, and hundreds more made homeless.

By the year 2000, such was the devastation and the danger from future eruptions that the southern part of Montserrat was declared an exclusion zone. People who lived in it had to move to the north of the island, or move abroad. Nine thousand people decided to do leave the island. Two thirds of the country had been closed down. In fact, there was a point when the government thought the whole island might have to be evacuated.

However, large numbers of the Montserrat people were not prepared to go they were determined to get the country moving again. With only the northern third of the island now habitable, practically everything was changed around, remade or built from scratch. Locally grown food began to appear on the streets again and by the middle of 2002, it looked as if things were at last going to settle down for the first time in six years.

Then, in September 2002 it started all over again. Two thousand metre high clouds of ash, rock and scorching gas rose into the sky and a couple of pyroclastic flows began – but this time it was all in an area that was rated safe. A previously unaffected area was now under threat and it was added to the existing exclusion zone. This was terrible news for the hundred or so families who had to evacuate, yet again.

Until the eruption of the Soufrière Hills volcano, the economy of Montserrat had centred on tourism and related services. Tourism accounted for about one quarter of Montserrat's national income. The island's main export is electronic components, which are mainly shipped to the USA. The agriculture sector is small – cabbages, carrots, cucumbers and onions are grown for the domestic market. The volcanic eruptions in 1995 and 1997 led to the evacuation of Plymouth, the capital, and the people who left the island moved mainly to Antigua and Guadeloupe.

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Activities

1. Below is a list of 15 major volcanic eruptions that have taken place since 1995:

The world map below shows the location of the tectonic plates, their boundaries and the directions in which they are moving.

1. Mark on the map the locations of the volcanoes
2. Describe and explain the relationship between the locations of the volcanoes and the tectonic plates.

2. It is highly probable that the volcano on Montserrat will erupt again.

1. Working in small discussion groups and using both the background information above and the television programme, what plans would you make to reduce the impact of any further disruption to the people living on the island? (Think in terms of priorities: resources, aid and support).
2. Give a brief presentation of your conclusions to the rest of the class. What are the similarities and differences between your decisions and those of the other groups?

3. You are a journalist and have been asked to write an article about the volcanic eruptions on the island of Montserrat and the impact on its people. Write your article as if you were interviewing several people – a local resident living in the capital, Plymouth; a volcanologist who is investigating the volcano; and the mayor of Montserrat. What are the messages that each person would be trying to convey?

(You may like to read an article in the Washington Post which may help you: Montserrat Volcano Threatens Biggest Eruption
By Keith Greaves Associated Press Writer Tuesday, November 4, 1997; 8:17 pm)

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Links

This web page contains links to other websites that are neither controlled nor maintained by Channel 4 Television. Channel 4 Television is not responsible for the content of these sites and does not necessarily endorse the material on them.

http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/introduction.html An introduction to plate tectonics – Level: teachers

http://www.bbc.co.uk/science/horizon/
BBC Horizon – information about predicting volcanic eruptions and the work of Dr Bernard Chouet. The site contains the full transcript of the programme 'Volcanic Hell' – Level: teachers

www.wifak.uni-wuerzburg.de/fact98/mh.htm
A fact file about the geography, political, economic and social structure of Montserrat – Level: teachers

www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/monmedia/index.html
Official Press Releases from the Government of Montserrat about the volcanic eruptions on Montserrat – Level: teachers

www.volcanolive.com/contents.html
Volcano Live – up-to-the-minute news about the state of active volcanoes around the world – Level: teachers and students

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