Diedtra Henderson
YELLOWSTONE: Park lake hints at buildup to huge blast
Mon Aug 11 14:44:55 2003
64.140.158.62

Article Published: Sunday, August 10, 2003 - 12:00:00 AM MST Park lake hints at buildup to huge blast

http://www.denverpost.com/Stories/0,1413,36~53~1561852,00.html

Post Science Writer
YELLOWSTONE NATIONAL PARK, Wyo. - The mystery of the deep at picturesque Yellowstone Lake is a bulge that rises 100 feet from the lake floor, stretches the length of seven football fields, and has the potential to explode at any time.

Of all the life-threatening events that could happen at Yellowstone - from volcanic eruptions to massive earthquakes - this type of hydrothermal explosion is likely the most immediate, serious hazard in the park. So, scientists are trying to better understand possible warning signs.

The dome acts like the lid on a pressure cooker. A hydrothermal explosion releases pent-up pressure; in this case, letting loose 10-foot-tall waves, raining chunks of pulverized rock on land, and injecting a plume of steam and poisonous gases through the water. If the entire dome exploded, the explosion could carve an underwater crater stretching up to 2,300 feet across.

Scientists first noted a problem last summer, as they surveyed the lake. The sharp stench of rotting eggs - from hydrogen sulfide gas - was in the air, clouds of sediment choked the water and swarms of bubbles rose to the surface.

Could those be signs that an explosion is imminent?

It's a pressing mystery that a team led by a Colorado-based scientist will try to puzzle out this month.

In a scientific paper, Lisa Morgan said the "inflated plain" is "a potential and serious hazard and possible precursor to a large hydrothermal explosion event."

Morgan chose her words carefully in an interview near Indian Pond, a seemingly placid lake created by a similar hydrothermal explosion 3,000 years ago.

"We're not saying this structure is ready to blow," said Morgan, a U.S. Geological Survey research geologist based in Lakewood who specializes in volcanic terrain. "It's a significant feature. We're just not sure what it's going to do."

The dome may be just one more visible sign that hydrothermal fluids are on the move, seeping into vulnerable sediments and creating another potential hazard in a park that has already endured earthquakes and volcanic eruptions.

Already this summer, increased geothermal activity prompted park officials to seal off trails at one of the hottest geysers in the park for the safety of the more than 3 million annual visitors as well as the staff. Morgan wonders whether the same geothermal activity that inflated the dome is to blame for reawakening a nearby geyser that has long been dormant and for causing a 20-degree rise in water temperature at a nearby hot pool.

Geological treasure trove

Yellowstone, the world's best real-time geologic laboratory, is teeming with spewing geysers such as Old Faithful, along with rumbling earthquakes, superheated hydrothermal fluids seeping from vents, and sputtering mud pots, where acid has dissolved rock and the resulting heat and water make the mud bubble.

Yellowstone Lake, North America's largest high-altitude lake, shares this powerful geology.

Despite the lake's rich history, no one had created an accurate map of Yellowstone Lake until recently. Ferdinand Hayden gave it a try in 1871, attaching wool sails to an 11-foot boat and exploring 130 miles of coastline. Hayden underestimated the coastline by some 11 miles.

For four years, Morgan's group has applied higher-tech solutions, ricocheting sound waves 220 million times off the lake bottom and taking other detailed measurements by airplane.

They found the lake bottom was paved by lava flows and scoured by glaciers, and that a few sections were dusted by fine sand likely swept there by earthquake-generated tsunami waves.

The lake's geology lay concealed by its waves until revealed by the high-tech detective work. The bathymetric maps also sketched the contours of a swollen lump of land deep beneath the surface.

The inflated dome is pockmarked by hydrothermal vents where acidic fluids gnawed away at lava.

Bobbing atop Yellowstone Lake, scientists saw worrisome signs that the vents were active: The water churned with bubbles. A wide swath of water was turned opaque by finely dissolved sediments. The overpowering stench of hydrogen sulfide filled the air. And water temperatures 65 feet below the surface shot as high as 187 degrees Fahrenheit.

Dropping a submersible rover for a closer look confirmed that up to a gallon per second of shimmering water shot from hydrothermal vents as large as coffee cans.

This summer, Morgan will float in a tricked-out boat atop the lake, ricocheting more sound waves off the lake floor to closely map any new curves.

Dave Lovalvo, owner of Connecticut-based Eastern Oceanics, will pilot the $500,000 rover he built, directing its probes into vents spewing superheated hydrothermal fluids. The rover, as souped-up as Alvin without the sleek exterior and spunky name, wears a row of orange spheres to stay buoyant and sports a video camera as its eyes.

Pat Shanks, a Lakewood-based USGS geochemist, will study water samples for arsenic, antimony, mercury, tungsten and molybdenum, signature chemicals carried within geothermal fluids.

The heightened scrutiny is to determine whether the bulge is living and evolving.

Until that's known, researchers such as Robert B. Smith, author of "Windows Into the Earth: The Geologic Story of Yellowstone and Grand Teton National Parks," doesn't know what to make of Morgan's bathymetric maps.

"I guess the question is, is it actually going on today or is it a discovery of a mound that had inflated sometime in the past? I really don't know," said Smith, a geology professor at the University of Utah who has done 40 years of research at the park.

Park's explosive history

Scientists are at the early stages of discovery at Yellowstone. Until it's clear whether the dome is rising, it's difficult to determine how much explosion risk it poses.

What scientists do know is that larger geologic forces have been at work at Yellowstone for millions of years, creating mountains or erasing landscapes with equal ease during the violent episodes. Like the lungs of a sleeping giant, the larger Yellowstone Caldera - a geologic furnace providing the heat and molten rock that fuels the park's geothermal activity - rose from 1923 to 1985. The huge pool of hot rock lying 125 miles beneath Yellowstone slightly dropped from 1985 to 1995. From 1995 to 2001, the caldera again rose, accompanied by swarms of earthquakes.

"That's why we named this 'the living, breathing caldera,"' Smith said.

This summer already has shown signs that the caldera remains wide awake.

Norris Geyser Basin, the hottest thermal area in Yellowstone, sprouted new mud pots. Ground temperature on the trail soared to 200 degrees Fahrenheit, too hot to touch. Porkchop Geyser, dormant since 1989, erupted on July 16.

Park officials responded by barring access to half of the 2 miles of Norris Geyser trails.

This summer, Smith and a team of scientists are closely studying Norris Geyser, where nearly 4,000 visitors passed in a single week in July.

It's all part of a larger effort to determine how often to expect geologic events ranging from small hydrothermal explosions to massive earthquakes. What scientists fear is a repeat of the 1959 Hebgen Lake earthquake near Yellowstone that killed 28 people, triggered a massive landslide and caused $13 million in damages.

Preliminary study indicates that quakes that large are likely to occur every 100 or so years. And it's been 70,000 years since the last major volcanic eruption at Yellowstone.

But hydrothermal explosions, large and small, are much more common.

For now, no restrictions are planned at Yellowstone Lake.

"There is no cause for alarm, at this point, and there may never be," said Jake Lowenstern, scientist-in-charge at USGS' Yellowstone Volcano Observatory in Menlo Park, Calif. The observatory tracks volcanic and hydrothermal unrest at Yellowstone as well as earthquakes.

"We need to know more about how long this feature (the dome) has been in existence. If it's been there for quite a while, perhaps it's relatively stable and doesn't pose any significant hazard."

Reach Denver Post science writer Diedtra Henderson at dhenderson@denverpost.com  or 303-820-1910.



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