SMOKING GUN’ PROVES UNDERGROUND VOLCANISM IN OREGON
January 10, 2000
Contact Ross West (541) 346-2060
Source: Michael Manga (541) 346-5574; e-mail mmanga@newberry.uoregon.edu
EUGENE–Observed from the surface, the rocky peaks of Oregon’s central Cascade Mountains have appeared quiet since the violent eruption that formed Belknap Crater 1,300 years ago. Now, new research conducted by University of Oregon geologists indicates that, below ground, the central Cascades are anything but quiet.
While lots of volcanic research is focused on flowing streams of molten lava, the UO researchers came to their findings by studying another kind of flow–spring-fed streams and rivers. Their findings were published in a recent issue of the scientific journal Geology.
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We found that the cold springs of the Central Oregon Cascades discharge large amounts carbon dioxide. The carbon dioxide is coming from underground magma, or hot liquefied rock," says Michael Manga, a UO assistant professor of geology. "We have long suspected underground volcanic activity, but until now we didn’t have any hard evidence for it–no smoking gun."How can water tell the story of underground volcanic activity?
Under the great pressures within the Earth, liquid rock contains many dissolved gases, in much the same way that champagne holds gases that, once the cork is popped, become bubbles. The geological equivalent of a cork popping is a volcano erupting. For example, when Washington’s Mount St. Helens erupted in 1980, huge volumes of gas escaped into the atmosphere.
"Our work has shown that in areas with lots of ground water and no erupting volcanoes, such as the central Cascades, the carbon dioxide from the volcanic source reacts with underground spring water and changes to bicarbonate, or common baking soda," Manga explains. "The bicarbonate is a form of carbon dioxide that dissolves in water and generally stays there."
Manga and his team tested water from many of the large springs in Central Oregon, including the headwaters of the Metolius River northwest of Bend.
"Our calculations show that thousands of tons of carbon dioxide from volcanic sources may be released annually from each of the spring-fed streams and rivers in Central Oregon, such as the Metolius and the Deschutes," he says.
Getting an accurate view of what is going on hundreds to thousands of meters underground, as Manga and his team have done, is difficult, even with the aid of sophisticated techniques such as seismic imaging.
"But we have so much water here in Oregon we are able to use it to learn what is happening below," Manga notes. "And what we now know is that a great deal of volcanic activity is going on down there."
In addition to telling Oregonians about their local landscape, the findings also may have more global implications.
Carbon dioxide is a "greenhouse gas," linked to global warming. In its fairly stable bicarbonate form, carbon dioxide does not directly contribute to the amount of the gas in the atmosphere. But it does clog up the so-called "carbon cycle" by which carbon dioxide is absorbed into water and thus scoured from the atmosphere.
The implications of these new findings could be significant, according to Manga, because they identify an additional source of naturally occurring carbon dioxide in the carbon cycle.
"This helps us understand how the carbon cycle and climate change worked in pre-historic times and thus how the Earth might respond to the huge volumes of carbon dioxide we’ve produced since the industrial revolution," he says.
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