Scientists Have Only Theories About Why Activity is Increasing

June 1, 2003
By MIKE STARK
Gazette Wyoming Bureau

YELLOWSTONE NATIONAL PARK – In the other-worldly landscape of Norris Geyser Basin, beauty, mystery and geology intersect. Its hot springs, brilliantly colored thermal pools, tempestuous geysers and spewing steam vents present the visitor with ever-changing wonders. Its inspirational show bespeaks secrets deep under the surface of the earth.

And these days Norris, Yellowstone’s hottest and most dynamic geyser basin, is talking plenty.

Steamboat geyser – the largest in the world and one of the most unpredictable, with dormant periods as long as 50 years – has erupted four times in a year.

Water in the basin is getting hotter and more is flowing through scoured channels into Tantalus Creek. The temperature inside Pork Chop geyser, which exploded in 1989, has risen by 8 degrees Celsius in recent months. Nearby, a swarm of about 100 earthquakes shook the area in 2000 and, more recently, a series of new steam vents cracked a wooded hillside near Nymph Lake.

Something is afoot in the superheated chambers beneath Norris, but no one is sure exactly what.

“This is an increasing activity trend,” said Henry Heasler, the park’s lead geologist, standing on the wooden boardwalk just downwind from the huffing of Steamboat geyser. “Part of the scientific question now is: How do we define that trend?”

Norris sits on a series of faults that string toward Mammoth. The below-ground friction helped create some of the most recent eruptions in Yellowstone. There may be a direct connection with magma – molten rock miles below the surface – providing extra heat to the basin, said Jake Lowenstern, scientist-in-charge at the Yellowstone Volcano Observatory.

“Certainly one explanation could be that either magma or thermal fluids are moving up in this region,” Lowenstern said.

Park geologists have been busy the past year or so placing new devices around Norris to measure water flow and temperature and record the exact times of eruptions. Heasler said raw data would be made available for scientific work on what’s happening at the basin.

But some of the most enticing clues about Norris are coming from space.

Relatively new technology uses satellites to bounce radar off the earth to measure how much the ground is moving.

Deployed to help measure the in-and-out “breathing” of the Yellowstone caldera – the giant collapsed volcano in the center of the park – the radar picked up another system at work.

Just south of Norris basin is a bulge in the earth about 28 miles across and 7 miles deep that has pushed the ground up more than 5 inches since 1996, according to research by Chuck Wicks, a geophysicist with the U.S. Geological Survey in Menlo Park, Calif.

That kind of movement of the earth in the Norris uplift, also documented by University of Utah geologist Bob Smith, is considered rapid in the perspective of geologic time.

The discovery came as a shock to geologists who, until then, only knew of two “resurgent domes” in the caldera that slowly puffed up and down with the underground movement of hot water and magma.

This third bulge, which sits partially inside and partially outside the caldera, prompted a series of new questions about what’s happening beneath Yellowstone’s surface.

“It’s fair to say the Norris uplift came as a surprise,” said Dan Dzurisin, a Cascades Volcano Observatory scientist who has studied Yellowstone’s geology for years. “But it’s a continuation of the trend that for decades, each time we look at Yellowstone we discover something that surprises us.”

Is the swelling ground south of Norris related to recent activity like the return of Steamboat and hotter temperatures?
There are theories, but no conclusive answers.

“That’s a tough one. It’s tempting to say there must be a connection, but to go the next step and explain what that connection is could be pretty tough,” Dzurisin said.

He thinks that, at more than seven miles, the source of the uplift may be too deep to directly affect the hydrothermal system at Norris. It’s possible, he said, that the bulge is opening underground fractures and allowing more heat to escape, which raises water temperature and stirs up activity near the surface.

“But that’s a long pipeline,” he said.

Wicks said it seems likely there’s a connection between the inflating land and episodes at Norris, including recent Steamboat eruptions.

The dome may be reconfiguring the underground system of heat, molten rock, water and channels to allow an extra boost of heat or hot water into the system, Wicks said.

“This could be tweaking the shallow plumbing system somehow ... rearranging stuff so things can get up (to the surface) faster,” he said.

An earthquake in Alaska last fall touched off hundreds of earthquakes in Yellowstone in the following days, showing that the park’s geology can be influenced even by faraway events, he says.

“This whole area is sensitive to small movements in the system,” Wicks said.

The latest information on the Norris uplift shows that its expansion slowed in 2001 and 2002.

Geologists theorize that the bulge eventually will subside, as did the other two domes in the park.

While scientists try to understand the connection with Norris, they’ll also try to figure out whether the newly discovered dome, which geologists say had probably been there for a long time before it was found, is linked to the other two domes, Sour Creek and Mallard Lake.

Smith, from the University of Utah, pioneered work in Yellowstone showing that the caldera continually “huffs and puffs.”
Portions of the caldera rose more than 3 feet between 1923 and 1984 and then dropped nearly 8 inches from 1985 to 1995, according to Smith’s research. Measurements in 1995 and 1996 showed that the caldera floor was rising again and then started to fall in 1997.

The rising is probably caused by magma rising toward the surface but never quite breaking through, Smith theorized.

Dzurisin says there’s some anecdotal evidence that could link movement of the two domes to the Norris uplift, but it’s tenuous.

“As we watch these three things more closely, we’ll see how they interact, if one goes up and the other goes down,” he said. “We’ll just have to see.”

Even if a connection between the domes is established, questions about new activity at Norris may not be answered.

Geologists are still trying to understand the specific links between the deep churning magma beneath the park and spurting of geysers, steam vents (called fumaroles) and hot springs.

Heasler, the park geologist, says all possible explanations of events at Norris are being considered.

“You can go from two extremes: the climate and the atmosphere to the magma chamber ... and everything in between,” Healser said.

Either way, he said, it’s an exciting time to be watching Norris.

“With so much of this, we just don’t know,” Heasler said. “But that doesn’t mean it can’t be discovered.”

http://www.montanaforum.com/rednews/2003/06/02/build/parks/activity2.php?nnn=3