It's not "Dante's Peak," but it has scientists increasingly intrigued. Compared to the fictitious Hollywood volcano, the Three Sisters are harmless. Recent ground swelling, earthquake and volcanic gas emissions around South Sister, however, have prompted scientists to step up research on one of the most prominent volcanoes in Central Oregon.
A team of scientists from the U.S. Geological Survey (USGS) and Central Washington University have just finished five days of increased field work on South Sister.
The scientists weren't worried about an imminent eruption, but were excited to learn more about one of the world's more active volcanic chains.
Preliminary findings suggest a small amount of magma, or molten rock, may be creating pressure a few miles underground, causing the ground to swell, rumble and emit gases.
The Cascades routinely have tiny earthquakes, but only South Sister has active ground deformation. Scientists narrowed the time when the bulge occurred to 1998 to 2000. But they lack enough historical data to know if the swelling, earthquake and gas emissions are increasing or are just normal behavior for the Three Sisters, which may routinely undergo tiny earthquakes that occur commonly in other volcanoes.
The additional seismic monitoring and satellite radar equipment scientists installed could start providing answers as early as next month.
"It's an interesting opportunity to better understand the process of how the Cascades stay alive," said Willie Scott, the scientist in charge of the USGS Cascade Volcano Observatory in Vancouver, Wash.
Ferried around the rugged area by a helicopter, the six-member team took ground and air readings from previously installed equipment and set up more monitoring equipment in dozens of locations across 10 square miles.
The crew also took readings from existing tilt stations and installed more Global Positioning System receivers and compared them with benchmarks set up in 1985 to measure whether the ground had tilted.
The leveling equipment is similar to that used by homebuilders to ensure straight lines. In all, more than two dozen tilt stations, GPS stations and seismometers now cover the Three Sisters area.
Carbon dioxide, sulfur dioxide and hydrogen sulfide emissions in the air will be compared to readings in May to see if they have increased. More water samples from creeks in the area will be taken later.
The seismic, gas and deformation readings could eventually help in the holy grail of volcanologists - being able to make accurate long-term forecasts about eruptions.
The South Sister presents an unusual opportunity to gather data that could make such predictions a reality, Scott said. "We're excited because we're in the business of studying volcanoes, and you always learn more from volcanoes that are active," said USGS geologist Dan Dzurisin. "We're ramping up our efforts on the Three Sisters."
The South Sister has exhibited the three traditional pre-eruption signals - ground deformation, gas emissions and earthquakes - but the signs have been weak, Dzurisin said. Although the South Sister eventually will erupt like it and all volcanoes have done and will do again it will give strong warning signs long before erupting, he said.
From Mount Baker in northern Washington to Lassen Peak in northern California, the Cascade volcanoes have erupted periodically for thousands of years - Mount St. Helens most continuously and most recently.
Many Cascade peaks remain active to varying degrees, including Mount Hood, which routinely has swarms of minor earthquakes. In May, scientists' attention was drawn to the Three Sisters, which have not erupted in about 2000 years, after they detected a swelling of the earth's crust near the South Sister.
The bulge - 4 inches high and from nine to 12 miles in diameter - is three miles west of the South Sister. The bulge was detected with relatively new technology called satellite radar interferometry, which uses radar data taken from space to create images of the surface of the earth. The images are compared over time to show changes.
Tests of Separation Creek, which drains the area where the bulge was detected, show slightly higher than normal levels of chloride and sulfide, gases associated with volcanic activity.
Earlier this month, the USGS detected a minor earthquake, a 1.9 magnitude, around South Sister, with a seismometer installed in May on a nearby peak, The Husband.
Scientists monitoring Central Oregon with older technology over the last 20 years could only detect quakes as small as 2.5 before the new seismic monitoring station was installed. The scientists are working in cooperation with Deschutes and Willamette national forest officials.
The USGS Cascades Volcano Observatory, which has about 50 scientists, makes several field research trips a year, monitors seismic activity around the clock, advises local authorities on emergency evacuation plans, educates the public and publishes its research results in booklets designed for the general public.
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