Why Study Volcanic Gas
A famous Japanese geochemist, Sadao Matsuo, once said that "Volcanic gas is a telegram from the earth's interior." By studying volcanic gases, volcanologists hope to recognize changes in abundance or composition that might signal reawakening of a dormant volcano or portend an imminent eruption at an already restless volcano.
Another significant component of volcanic gas research involves measuring the quantities of gas that volcanoes release to the atmosphere. Huge amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere during major explosive eruptions. Some gases, such as carbon dioxide, contribute to global warming, while others, like sulfur dioxide, can cause global cooling and ozone destruction. Studies of volcanic emissions will allow scientists to compare volcanic gas output to emissions from man-made sources and to assess the effects of both past and future eruptions on Earth's climate.
How Are Volcanic Gases Studied?
Customarily, gases are collected directly from volcanic fumaroles (vents), then transported to an analytical laboratory for detailed chemical analysis.
A new approach involves installing chemical sensors in or near volcanic vents and linking them to radio telemetry devices to provide a continuous readout on one or more gases. This method can detect significant short-term releases of gas that will usually be missed by occasional sampling.
Finally, emissions of certain gases can be measured in the plume discharging from a volcano. Scientists use an optical spectrometer mounted in an airplane and flown through or beneath a volcanic plume or in a satellite measuring the plume from space. This equipment provides a measure of the total output of one or more gases and is useful in understanding how much volcanic gas is released into the atmosphere.
What Have We Learned?
Studies by scientists at the U.S. Geological Survey (USGS) have revealed the compositions and amounts of gases released from several active volcanoes in the U.S. (Alaska, Cascades, Hawaii). As an example, USGS scientists studying the gases of Mount St. Helens have determined that about 2 million tons of sulfur dioxide were emitted between 1980 and 1988. Sensors aboard a satellite detected about 1 million tons of sulfur dioxide injected into the stratosphere during the main eruption on May 18, 1980. Another half-million tons of sulfur dioxide was dissolved in water droplets attached to ash particles that eventually fell to earth. The remaining half-million tons was emitted from the volcano during the eight years following the initial eruption. These measurements allow important comparisons with sulfur dioxide emissions from power plants and other man-made sources.
Careful study of Mount St. Helens' gases using chemical sensors installed on the dome along with airborne measurements of sulfur dioxide revealed periods of increased gas emission prior to four dome-building eruptions during 1984-86. This observation is an important first step in developing the ability to predict eruptions by monitoring gases.
In summary, the study of volcanic gases contributes important new information related to global climate change and may lead to the development of an effective tool for predicting volcanic eruptions. Source: U.S. Geological Survey
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