Predicting and Preparing
for Volcanoes
Prediction methods for volcanic eruptions are more reliable than those for earthquakes.
Some volcanoes such as Mount Etna in Italy are monitored all of the time because of the risk
they pose to populated areas nearby.
I. Methods
The main methods that can be used to try to predict eruptions are outlined below.
1. Earth tremors
Magma moving around inside a volcano and rising up through cracks underground will cause
small earth tremors (shaking). These can be measured by seismometers just like earthquakes
are. Earth tremors don't always mean that an eruption is on the way, but if the tremors
increase, in amount or strength, it shows the activity in the volcano is increasing and an
eruption is more likely.
2. Increase in gas
Volcanoes release lots of different gases into the air, the main ones being carbon dioxide
and sulphur dioxide. Air samples can be taken from near the volcano vent; significant
increases in the amount of gas can show an eruption is on the way.
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3. Rise in temperature
As magma begins to rise to the surface it can raise the temperature of the land. Thermal
imaging sensors and satellites can be used to measure temperatures around a volcano.
4. Changes to lakes
The water in a lake can get warmer as magma rises to the surface. The lake can also look like
it is getting fuller. This is because many lakes have underground chambers that are full of
water. As the magma and gases rise this water is pushed into the lake, increasing the water
level.
5.
Ground deformation (changing shape)
Sometimes a volcano can become blocked by a plug of hardened magma. If this happens
then as magma rises from the mantle into the volcano it has no way of escaping. This makes
the pressure in the volcano rise and will cause the shape of the volcano to change. Ground
deformation can show that a pyroclastic flow may occur (a huge and deadly explosion in the
volcano). One of the best known examples of this is the eruption of Mount St Helens in the
USA in 1981. Before the eruption the north side of the volcano started to bulge upwards
because of the magma trapped beneath. The ground deformation can not be seen by just
looking at the land, measuring sensors are used by volcanologists. (Volcanologists are
scientists who study volcanoes).
Prediction of volcanic eruptions is expensive; it requires highly trained staff and a great deal
of specialist equipment. It is also important that people living near a volcano are well
prepared and know what to do in the event of an eruption.
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II. Preparing for volcanic eruptions
We cannot stop volcanic eruptions from happening so to protect people and reduce death
rates authorities need to produce a clear and detailed plan for emergency services and
members of the public.
1. Authorities

Operations centre away from danger zone so that rescue and relief can be
coordinated if an eruption does happen.

Exclusion zone set up around volcano so members of the public are not caught up in
an eruption.

Evacuation plans in place so that members of the public can be quickly moved to a
place of safety.

Education plans set up so that people know what to do in the event of an eruption
and are less likely to panic.

Have designated zones where people can get food, water and medical supplies in the
event of an eruption.

Have good communication systems in place that won't be disrupted in the event of
an eruption.
2. Emergency services

Hold practise runs to ensure that all staff know what to do in the event of an
emergency.

Make sure there are alternative routes through the city in case roads are blocked.
3. Members of the public

Need to stay calm as follow instructions
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
Have an emergency kit ready with basic medicines, torch, water, dried and tinned
food, ID etc.

Be ready to evacuate and not stay behind to try to protect possessions and property.
III. Examples
Although prediction methods are better for volcanoes than earthquakes it is not an exact
science and mistakes are still made. Two well known examples are described below.
1. Mount St Helens (USA) – 1981
Scientists predicted the eruption of Mount St Helens in 1981 because of the ground
deformation on the side of the volcano. They created a 5 mile exclusion zone in the forests
around the volcano. When the volcano erupted however it didn't erupt upwards as they
thought but out of the side. This meant that they pyroclastic flow went along the ground and
travelled far further than expected. 54 people, many of them holiday makers and hikers who
were outside of the exclusion zone, lost their lives. The eruption happened on a Sunday
morning, if it had happened on any other day the death toll would have been much higher as
hundreds of people would have been at work in the saw mills and lumber yards in the forest.
2. Nevado del Ruiz (Colombia) – 1985
In the days before the eruption of Nevado del Ruiz ash and smoke were seen coming out of
the volcano and an evacuation of surrounding towns and villages was started. A lack of well
qualified staff who could read other warning signs meant that when the ash stopped so was
the evacuation and people went back home. A few hours later the eruption happened;
glaciers on top of the volcano were melted and the water mixed with the ash. 20 000 people
were killed by huge lahars (mud flows) that swept down the valleys.
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Multiple Choice Questions
1. Prediction methods for volcanoes are...
a) less accurate than those for earthquakes
b) more accurate than those for earthquakes
c) about the same as those for earthquakes
d) a very new technology so no one can really say?
2. It is important to monitor earth tremors because...
a) an increase in amount or size can indicate an eruption
b) a decrease in amount or size can indicate an eruption
c) they will often stop just before an eruption
d) an increase in amount and decrease in size size can indicate an eruption?
3. A volcano may be about to erupt if levels of...
a) oxygen increase around the volcano
b) carbon dioxide and sulphur dioxide decrease
c) carbon dioxide and sulphur dioxide increase
d) oxygen decrease around the volcano?
4. Ground deformation is...
a) a rise in temperature of the ground around a volcano
b) a fall in temperature of the ground around a volcano
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c) a change in shape of the ground around a volcano
d) a change in water levels in lakes near to a volcano?
5. Ground deformation is caused by...
a) magma rising through a blocked volcano and increasing pressure
b) moving magma making earth tremors inside the volcano
c) rising magma causing the temperature in the volcano to rise
d) gas rising up into the volcano vents?
6. Changes to lakes in a volcanic area can be...
a) a gradual decrease in depth
b) a gradual decrease in depth and an increase in temperature
c) a gradual increase in depth and an decrease in temperature
d) a gradual increase in depth and an increase in temperature?
7. To be ready for an eruption the authorities need to...
a) keep plans secret as much as they can so people won't panic
b) eruptions are impossible to stop so they can't really do anything
c) have road sweepers ready to get rid of the ash and lava
d) have a detailed plan that is well communicated to everyone?
8. To be prepared for an eruption members of the public need to...
a) leave as quickly as possible and in anyway they can
b) be calm, have an emergency kit ready and follow instructions
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c) stay in their homes to try to protect them from the lava
d) have their car ready so they can drive out of the city?
9. The 5 mile exclusion zone that was put around Mount St Helens...
a) worked really well and saved many lives
b) pointless as an exclusion zone wasn't needed for such a small eruption
c) didn't work because the volcano erupted out of the side
d) didn't work because the eruption was so big?
10. The evacuation of areas around Nevado del Ruiz was stopped because...
a) no one listened to the scientists
b) there were not enough trained staff to recognise the other warning signs
when the ash stopped
c) local people did not want to leave their homes
d) people had nowhere to go to?
Answers
1 = b, 2 = a, 3 = c, 4 = c, 5 = a, 6 = d, 7 = d, 8 = b, 9 = c, 10 = b.
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