Boiling bulge in Yellowstone Park lake worries scientists

Bulge in lake worries YNP scientists
By CAROLE CLOUDWALKER

Beneath the serene surface of Yellowstone Lake, where death from hypothermia comes within 30 minutes, seethes a boiling underwater world.

And like a pot too long on the stove, it could boil over, says U.S. Geological Survey geologist Lisa Morgan, Ph.D., of Colorado.

She and others from the USGS have been studying the hottest hot spot in the 7,731-foot elevation lake, a spot which Morgan has termed an "inflated plain." It lies south-southwest of Storm Point near Mary Bay, in the northern end of the lake.

Morgan, representing both the USGS and Yellowstone Volcanic Observatory, is in the process of mapping the lake floor with seismic reflection images. She uses a sonar system that emits sound waves. Morgan has taken 240 million soundings in the last four years.

She has found that temperatures along the inflated plain have been recorded at about 85 degrees 60 feet down, where the plain bulges up about 100 feet above the lake floor. (Park spokesman Cheryl Matthews says the lake rarely reaches more than 66 degrees at the surface by late summer, and is much colder deeper down.) The inflated plain stretches 2,100 feet - about the length of seven football fields - across.

"We think this is very young," something that occurred in the last few years, Morgan said.

"We're thinking this structure could be a precursor to an hydrothermal explosive event," Morgan said last week. "But we don't think this is a volcano."

If the bulge should explode, "we think it would create a large crater." But such an explosion, smaller versions of which created Indian Pond, Duck Lake and Mary Bay itself, would probably heat up the water temporarily, create high waves, spew poison gasses and other materials into the lake for a time, and leave a rimmed underwater crater.

Or it could do nothing.

Explosive events are, of course, not new in Yellowstone. Regional volcanoes once sent forth material across much of what is now the U.S.

"And Mary Bay is the world's largest hydrothermal explosion crater," Morgan said. Also lurking under water west of Indian Pond is Elliott's Crater, some 2,400 feet in diameter.

Powerful geologic processes contributed to the unusual shape of Yellowstone Lake, according to articles in the most recent edition of "Yellowstone Science," which describes Morgan's study. One of Morgan's objectives is to understand these processes.

Morgan is returning to Yellowstone in early August to further study the inflated plain, which she said "showed pretty radical changes" last summer. She and her USGS team will utilize a raft-like boat that resembles a high-tech Kon Tiki.

It carries, among other things, a small, red robotic submarine. The "ROV" will dive down to the underwater structure, land on it, scrape samples of rock and sand from its surface, and put in place devices that will measure any further changes to the structure.

By fall, Morgan and her team hope to prepare a "danger assessment" indicating how likely the plain is to explode, and if it does, what the scenario might be.

At this point in her work, Morgan has outlined two possibilities for the plain:

It could do nothing, and "freeze in time," becoming dormant.

It could explode, making a "large crater a couple of thousand feet in diameter."

If the dome blows, 10-foot waves could wash the lake shore, rocks and pieces of lake floor could be tossed into the air, and "chemicals containing toxic materials" could be discharged into the lake.

"There would be lots of water," Morgan said. Not the blue serenity of the present lake surface, but roiling, spewed-out hot water.

"But we don't think this is a volcano," Morgan said last week. Still, that possibility is being considered. She said what is causing the bulge is likely either carbon dioxide gas or steam. "We're trying to put monitoring equipment on the structure to see changes over time."

"We have no evidence there's any volcanic component" to the bulging dome, she added.