29 October 2004

Not Just Blowing Smoke

Dianna Hrabovsky

With the recent events at Mount St. Helens, I have become more aware and interested in volcanoes and the scientific study that goes on near and around them.

Besides checking for tremors and seismic activity, there are many other tests that are being done. It was amazing to find that even when there aren't any lava flows or ash being expelled from a volcano, there are other emissions that can be just as dangerous.

Just what can erupt from a volcano and why?

Examining the idea of what can come out of a volcano leads to the question of what is in a volcano. A volcano is not just a pit full of magma that fills up and occasionally overflows as lava . It is much more complicated than that.

One way magma is formed is when the plates move beneath the earth's surface and are pushed together. One will slide below the other. When a plate moves under an adjacent plate, a subduction zone is created. When something is subducted it means it descends. The plate bends down, and heating caused by friction and the earth's mantle causes a mass of molten material to be formed. This magma will slowly move up through the crust until it reaches a low pressure region where it can erupt violently or ooze out as lava.

Volcanologists know that swarms of earthquakes usually precede volcano eruptions. Perhaps there is also a correlation between an increase in earthquakes caused by plates shifting and volcanoes erupting. This would be an interesting assessment to make. However, even though the plates may shift, it could be a long time before the molten material would rise up enough to be noticed.

A volcano expels more than molten material or lava when it erupts. It also discharges gases and fragments of material in the form of dust or chunks of rock. It is not limited to any of these and can erupt all or some of them. Many times the dust and rock fragments can be very deadly.

If a volcano has an explosive discharge, it can blow a hot, forceful wind of these particles down the slopes and across vast expanses of land. This is called a pyroclastic flow. This word is made up of pyro, which means fire or hot, and clastic, which means sediment. The temperature of the pyroclastic flow near the eruption can exceed 650 degrees C (1,200 degrees F). Even far from the area of the explosion the temperature can reach around 200 degrees C (400 degrees F).

Sometimes the gases don't come out of the vents in the volcano but out of the ground itself. Released carbon dioxide can rise up through the ground and collect in unventilated areas, like mountain cabins, caves and recesses where the wind is unable to mix in normal levels of oxygen. If exposed to these places of accumulated CO2, a person can be overcome and pass out or even suffocate. Trees can also be affected by this rising carbon dioxide when their roots are exposed to the gas.

Researchers can predict what state a volcano is in by the kinds of gases it emits. Some of the gases that are especially important are carbon dioxide, sulfur dioxide and hydrogen sulfide.

An increase in the concentration of sulfur dioxide in the air near a volcano may indicate that magma is rising. This is because the reduced pressure in the rising magma allows the gas to be released. Increased sulfur and carbon dioxide levels can have many adverse effects on the ecosystem. Both gases can cause acid rain. Sulfur dioxide that reaches the stratosphere during major eruptions forms particles that contribute to ozone depletion. Other emissions from volcanoes include carbon monoxide, hydrochloric acid, and hydrofluoric acid. The most abundantly released gas is water in the form of steam.

There are many fascinating aspects of volcanoes to explore, including their history, formation, science and research. Included below are links to some of the web sites and a book I used to do my own research. I also enjoy watching the Mount St. Helens volcanocam which can be found using the link below. This site links to some interesting research and monitoring information.

References and links

"Volcanoes crucibles of change" by Richard V. Fisher, Grant Heiken and Jeffrey B. Hulen, Princeton University Press, Princeton, New Jersey, 1997.

Mount St. Helens Volcanocam (http://www.fs.fed.us/gpnf/volcanocams/msh/).

U.S. Geological Survey (USGS) (http://vulcan.wr.usgs.gov/projects/emissions/vgas_fsheet.html).