South Sister volcano in Oregon?s Cascade Range is beginning to show signs of erupting after lying dormant for thousands of years. Although indications are that an eruption is not likely to occur anytime soon, scientists are increasing their vigilance, which is located approximately 22 from miles from Bend, Oregon.
About a year ago, scientists at the U.S. Geological Survey (USGS) detected a bulge in the Earth’s crust near the base of South Sister volcano. Using high-precision radar data from satellites, Charles Wicks and his colleagues found that the ground west of South Sister had swelled about 4 inches since 1996. This swelling has continued at a rate of about 1 inch every year.
In addition to the ground swelling, Terry Gerlach and his colleagues at the USGS Cascades Volcano Observatory in Vancouver, Washington measured the chemistry of gasses in the air and springs around the bulging area. This chemistry shows that small amounts of gas from molten rock are showing up in some spring waters around the bulge.
The swelling near South Sister could be caused by the slow accumulation of molten rock around 4 miles beneath the area. William Evans and his coworkers in Menlo Park and at the Lawrence Berkeley National Laboratory in Berkeley, California have made models showing that molten rock is now accumulating beneath South Sister at a faster rate than in the past. Additional investigations are planned to help determine if the crustal bulge indicates that an eruption could occur anytime soon.
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Large dams in mountainous regions could threaten people living near them by stressing the Earth’s crust to danger levels, according to Chris Hartnady, of the department of geological sciences at the University of Cape Town, South Africa. He says there have been recorded cases in several countries of dam construction causing earthquakes. Large-scale mining can sometimes produce the same result, and parts of Africa are especially vulnerable because of the tectonic forces that are shaping the continent.
Hartnady says, “Large areas of the African continent are in an unstable, tectonically active state, and especially in the mountain regions substantial danger is posed to growing populations. The economic cost of seismic and volcanic disasters is likely to escalate dramatically during this century. Mountain areas appear very attractive places in which to site reservoirs or hydro-electric schemes. However, in east and southern Africa, these high-lying areas are usually associated with tectonically active belts near faults and rifts in the Earth’s crust.”
Bill McGuire, director of the Benfield Greig Hazard Research Center in London, says rising seismic and volcanic damage is a worldwide problem. “There’s no question that if you dig a big enough reservoir, you’re going to get earthquakes,? he says. “The Three Gorges Dam in China is going to be a big problem. There’s also the worry that if you build a dam in mountainous terrain that you will get landslides as it fills.”
A huge landslide behind the Vaiont dam in northern Italy in 1963 took the lives of over 2,500 people when a wave of water and debris spilled over the dam and swept away a small town. In late October 1995, the reservoir behind the Katse dam in Lesotho began to fill. Days later people started feeling earth tremors, and one measuring 3.1 on the Richter scale was recorded on 3 January 1996. “I am positive that was cause and effect. In 1964, a dam was built at Koyna in India’s Western Ghats. There was a big earthquake in the region in 1967 – cause and effect again,? says Hartnady. “So build dams if you must, but engineer them much more sensitively than we do now.”
Africa’s detailed seismological monitoring goes back only about 40 years, Hartnady says. But he is confident that science means it will soon be possible to predict earthquakes much more accurately. “I can’t tell people now when the risks will become acute. There could be a catastrophe tomorrow, or we could get through this century without one?The sooner we begin sophisticated monitoring, the sooner we’ll have the answers.”
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