Early fall in Central Oregon is a splendid time to roam the outdoors – to hunt or fish, to hike or kayak, or to measure a crustal uplift.
Huh? Oh, yeah: the “bulge.” That’s what non-scientists have called the phenomenon revealed earlier this year, west of the South Sister in the Three Sisters Wilderness Area.
As you can read in detail on the Web at http://vulcan.wr.usgs.gov/Volcanoes/Sisters/WestUplift/, U.S. Geological Survey scientists interpret the slight (4 inches is pretty slight in geologic terms) ground uplift and weak gas emissions as evidence that a small amount of magma, or molten rock, may have been intruded deeply into the area. Although small in height, the area of the uplift is wide, covering 9 to 12 miles in diameter.
Recently, scientists from the USGS Cascades Volcano Observatory in Vancouver, Wash., and Central Washington University, working with Willamette and Deschutes national forest staffs, spent five days conducting on-the-ground and aerial surveys of the ground deformation and gas emissions. Dr. William E. Scott, a USGS scientist studying the uplift, also took part in a public meeting in Bend; a second is scheduled Tuesday, Oct. 2 from 7-9 p.m. at the Sisters/Camp Sherman Fire Hall, 301 S. Elm in Sisters.
The bulge was detected using a special process called “radar interferometry,” which employs satellite data to measure minute changes in elevation.
One thing that scientists have stressed is that there is no immediate danger of a volcanic eruption or other hazardous activity from the swelling, or uplift. But that hasn’t stopped the public from guessing and wondering what could be happening, and what will happen in the future.
Then there was the breathless story in the Weekly World News tabloid this summer, headlined: “Giant Bulge in Oregon Full of Gold!” Indeed, a “researcher” from an unknown center in Geneva claimed the bulge could spew a fountain of molten gold 500 feet into the air, creating a new “gold rush” on surrounding properties – as long as you weren’t close enough at the time to be fatally scalded.
Scientists have successful week of work at uplift site
Okay, back to reality. Scientists focused on two main activities during their visit to the area last week. First, a helicopter ferried crews and equipment to spots where crews reworked level lines and benchmarks installed around South Sister in 1985, to provide baselines to assess future ground deformation. They also used leveling gear and Global Positioning System (GPS) receivers to measure the deformation over those 16 years, to try to confirm the uplift measured from satellites between 1996 and 2000.
Also, a helicopter carrying several instruments flew over the uplift area at low altitude, to repeat a gas monitoring survey done in May that measured slightly elevated carbon dioxide readings.
“It went well,” Scott (called “Willie” by his friends) said late last week from his Vancouver office, before hitting the road once again. “It was beautiful – five full days. We got everything done we wanted to get done.” So far, he said, “We don’t have many answers. We’re still reducing it to numbers.”
Weather-wise, the team’s timing was pretty good, too: Rain and cooler temperatures moved into the area shortly after the group finished its work.
Larry Chitwood, the Deschutes National Forest’s geologist for many years, introduced Scott at the Sept. 17 meeting.
“If you’ve been in Central Oregon for very long, you know it’s volcano country,” Chitwood said, with about 600 in the area, including such noteworthy sites as Pilot Butte and Newberry Crater.
Researcher calms fears, gives primer on volcanic mechanics, ash and the rest
Scott began by restating the key: “There’s no reason why anyone should be concerned. It’s not that there’s an eruption that’s imminent.” And then, in jest, he added, “The bulge is not made of gold.” In fact, he said, “We (scientists) don’t call it a bulge. Twenty years ago, Mount St. Helens had a bulge, and it was growing five feet a day.” (Now THAT’s a bulge.)
There have been numerous eruptions of Cascade volcanoes in the last 4,000 years, as the geologic record indicates, including several in the Three Sisters region about 2,000 years ago. The eruptions seem to happen in groupings of activity, then periods of dormancy.
Scott explained how volcanoes work, from the magma down deep to the volcanic gases that escape through small openings called fumaroles and a term Northwesterners learned two decades ago: pyroclastic flows, high-speed avalanches of hot ash, rock fragments and gas that can move down a volcano’s slopes during explosive eruptions at up to 150 mph, with temperatures as hot as 1,500 degrees.
While most of that happens in wilderness or very remote areas, not so the mud or debris flows called lahars, which can rush down valleys and riverbeds at 20 to 40 mph for distances of more than 50 miles. The powerful flows that can rip up and carry trees, houses and huge boulders have been one of the deadliest volcano hazards, carrying so much rock debris that they appear to be fast-moving rivers of wet concrete.
Scott then focused his comments on the volcanic ash that can fall many miles from a volcano, depending on how the wind blows. “Heavier ash fall can collapse roofs,” he said, adding that Central Oregon roofs probably would fare well in all but the heaviest ash fall, since they are engineered to handle a few feet of heavy, wet snow.
“Bend has been subjected to relatively massive eruptions in the past,” Scott said, with debris from pyroclastic flows 20 to 25 feet in depth. Even a “very small ash fall, a few inches” could clog gutters and eaves, not to mention the affect on vehicles and electrical equipment. “Seldom life-threatening, always a nuisance,” he said.
Scientists still have much to learn about what’s going on beneath uplift
The researcher also talked about the two kinds of volcanoes: major composite volcanoes, like Mount Rainier and Mount Baker, long-lived, with a wide variety of eruption styles, potentially highly explosive; and mafic volcanoes, which range from small cinder cones to large shild volcanoes like North Sister and Belknap Crater. They have more basaltic magma and are typically short-lived, with typically mild eruptions, and which create lava fields, and of which there are hundreds in Central Oregon.
One of the big questions for scientists is whether the uplift is a process that will create a new mafic volcano, or whether it’s related to the “plumbing” beneath the Middle and South Sisters, which eventually could lead to a more explosive eruption of one of the larger composite volcanoes.
“We have no way of knowing,” Scott said. “We don’t know a lot of details about what it looks like under volcanoes.” But it’s believed that the molten rock (magma) 50 to 60 miles deep pushes up to a depth of five or six miles, creating surface deformation and gas rising to the surface.
The bulge everyone is talking about now was found earlier this year by a scientist working at a USGS observatory in Menlo Park, Calif., comparing two satellite images and looking for changes. The process doesn’t work so well when thick stands of trees or heavy snow cover the ground. But when the changes in depth are given colors, a telltale “bull’s eye” effect can emerge – and it did three miles west of the South Sister, near an old mafic volcano called “the Husband,” much as has been seen in the Aleutians, the Galapagos Islands and Hawaii, Scott said.
In May, the scientists worked with Steve Otoupalik, the wilderness area manager on the McKenzie-Blue River District, on how to bring in monitoring equipment with minimal impact on the area. They installed a seismic monitor and GPS antenna, powered by two small solar panels and tucked in a spot barely visible from any distance. The signal is sent to a receiver at the Pine Marten Lodge on Mount Bachelor, then by phone to the University of Oregon, which processes the signal and puts it on the Internet for scientists to study.
“Lots of things make squiggles” on the seismograph, Scott said, such as rockfalls and high winds. It also can measure small earthquakes that went undetected before, such as the first one, recorded on the south flank of South Sisters on Aug. 21, a whopping 1.8 in magnitude on the Richter scale, and unlikely to be felt even close by. There have been other “tiny events,” Scott said, so it’s clear there’s “not a lot of seismic activity at the moment.”
Scientific work in wilderness area always `a balancing act,’ manager says
Otoupalik said permanent structures and motorized vehicles are prohibited in the 286,000-acre wilderness area.
“It’s a balancing act between what is really needed scientifically and the impact,” he said. “There’s nothing that says the activity can’t take place. It just needs to be sensitive to wilderness issues. … They had some constraints and we had some constraints.”
For example, it was decided that with the amount of material that needed to be brought in for the seismograph and GPS unit, a chopper would be less intrusive than doing so by backpack or on a pack mule. But the mules were used for those needing to head in and take gas readings from more than a dozen sites, using sophisticated gear in very rugged country.
The impacts have been “relatively benign” so far, the wilderness manager said. But if it’s decided that more instruments are needed, there would be a new level of involvement in those decisions – especially if uses needed to be limited, due to hazards to hikers.
The USGS has paid for another photographic pass over the site this fall by an ailing European satellite that’s somewhat hard to steer, Scott said. So by next year, with the added data, a clearer picture of what’s happening should emerge.
In the meantime, Scott said, scientists are working with local officials for emergency and response planning – not of the kind that have prompted school evacuation drills near the slopes of Mount Rainier, but preparation nonetheless.
Scott figures the magma intrusion is probably not over. “It could be an ongoing process, a hydrothermal system process by which volcanoes stay alive,” he said. And it may be happening elsewhere, just be harder to detect in areas always covered by dense forests.
“Our understanding of volcanic systems is pretty primitive, compared to all the questions people would like to have answered,” the USGS researcher said. Which is precisely why they keep at it, and lots of folks pay attention to what they learn.