predicting volcanic eruptions


Since volcanologists are usually uncertain about an eruption, officials may not know whether to require an evac- uation. If people are evacuated and the eruption doesnt happen, the people will be displeased and less likely to evacuate the next time there is a threat of an eruption. The costs of disrupting business are great. However, scientists continue to work to improve the accuracy of their predictions. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL:

gas emissions

Gases may be able to escape a volcano before magma reaches the surface. Scientists measure gas emissions in vents on or around the volcano. Gases, such as sulfur dioxide (SO2 ), carbon dioxide (CO2 ), hydrochloric acid (HCl), and even water vapor can be measured at the site (Figure 1.1) or, in some cases, from a distance using satellites. The amounts of gases and their ratios are calculated to help predict eruptions. Scientists monitoring gas emissions at Mount St. Helens.


remote monitoring

Some gases can be monitored using satellite technology (Figure 1.2). Satellites also monitor temperature readings and deformation. As technology improves, scientists are better able to detect changes in a volcano accurately and safely.



Moving magma shakes the ground, so the number and size of earthquakes increases before an eruption. A volcano that is about to erupt may produce a sequence of earthquakes. Scientists use seismographs that record the length and strength of each earthquake to try to determine if an eruption is imminent.

slope deformation

Magma and gas can push the volcanos slope upward. Most ground deformation is subtle and can only be detected by tiltmeters, which are instruments that measure the angle of the slope of a volcano. But ground swelling may sometimes create huge changes in the shape of a volcano. Mount St. Helens grew a bulge on its north side before its 1980 eruption. Ground swelling may also increase rock falls and landslides.

predicting volcanic eruptions

Many pieces of evidence can mean that a volcano is about to erupt, but the time and magnitude of the eruption are difficult to pin down. This evidence includes the history of previous volcanic activity, earthquakes, slope deformation, and gas emissions.

history of volcanic activity

A volcanos history how long since its last eruption and the time span between its previous eruptions is a good first step to predicting eruptions. Active and dormant volcanoes are heavily monitored, especially in populated areas.

instructional diagrams

No diagram descriptions associated with this lesson


scientists can predict exactly when a volcanic eruption will take place.

a) true

-->  b) false

magma and gas building up in a magma chamber before an eruption cause

-->  a) ground deformation

b) dome formation

c) lava flows

d) all of these

which of these geological tools would not be useful for determining if a volcano might erupt?

a) tiltmeter

-->  b) compass

c) satellite

d) seismograph

which of these could tell you that a volcanic eruption is imminent?

a) earthquakes

b) gas emissions

c) ground swelling

-->  d) all of the above

satellites can monitor this coming from a volcano.

a) gases

b) temperature

c) deformation of land

-->  d) all of the above

gases that are emitted by a volcano include

a) nitrogen

b) carbon tetrachloride

-->  c) carbon dioxide

d) oxygen

even if a volcano is dormant, scientists may still monitor it for an eruption.

-->  a) true

b) false

the number and the size of earthquakes decrease before a volcanic eruption.

a) true

-->  b) false

a visible sign that mount st. helens was about to erupt in may 1980 was

a) a dome growing on the top of the cone

b) ash spewing out the top

-->  c) a bulge on its north side

d) all of these

volcanologists are always certain about when to require an evacuation due to a volcanic eruption.

a) true

-->  b) false

diagram questions

No diagram questions associated with this lesson