SCIENCE GEOTHERMAL ACTIVITY : Concern Over Crater Lake Focuses New Attention on Freshwater Bodies
On the bookcase behind biologist Jim Milestone’s desk at Crater Lake National Park is a reminder that the National Park Service is “gravely concerned” about geothermal development just outside the park.
The park service was so concerned that drilling for heat left by a volcano might rob the lake of clarity that it paid more than $600,000 for a series of dives to look for hot springs. It also focused attention on deep lakes, long the neglected stepchildren of oceanography.
“It is finally begining to sink in that, gee, if we really want to know this planet, we’ve got to get down under not only the oceans of the world, but the fresh water as well,” said Sylvia Earle, an oceanographer and head of Deep Ocean Engineering, the maker of Deep Rover, a one-person submarine.
“It awaited the last couple of years, a couple of crafty (oceanographers), the Park Service and an issue, concern about geothermal development, to awaken people to how much we did not know,” Earle said.
In August, Oregon State University oceanographers Jack Dymond and Bob Collier led 23 dives--13 seeking hydrothermal activity, five for geological samples and five studying biology--to the floor of the 1,932-foot-deep lake.
They are convinced that hot springs exist but did not find conclusive proof. They will spend a year on a report to help determine whether Crater Lake stays on a list of national parks with significant thermal features. If it does, Interior Secretary Manuel Lujan Jr. could block geothermal development to protect the lake.
What Dymond and Collier did find were mysterious blue pools of dense salty water on the lake bottom laden with carbon dioxide and radon; fluffy orange mats of iron-eating bacteria; elevated temperatures in rock anchoring the bacteria, and rust-colored spires resembling stalagmites.
At the deepest point of the lake, park biotechnician Mark Buktenica found tiny craters and a midge-fly larva.
Last year, Earle found ordinary green moss growing at the freshwater record depth of 725 feet.
“Part of it is the clarity of the water, but I think there may be more to it than that,” said oceanographer Bruce Robison of the Monterey Bay Aquarium Research Institute.
Indian legends ascribe the formation of Crater Lake to a battle between Llao, god of the underworld, and Skell, god of the surface world. Geologists date the cataclysmic eruption of Mt. Mazama at 6,850 years ago. The volcano collapsed, leaving a caldera that filled with rain and melted snow and became a world standard for lake clarity.
Scientists became concerned that the lake was losing clarity and in 1982, Congress ordered a 10-year study. The clouding appears to be caused by growth in the population of microscopic plants called phytoplankton. The Park Service discounts a theory that nitrates from a septic system on the rim were feeding the plankton, but it is going to remove the system anyway.
California Energy Co. filed leases just outside the park in the Winema National Forest, and in 1986 began drilling in search of geothermal energy. The company says it is impossible for its work to affect the lake.
Dymond began studying the lake in 1984. “We found these unusual chemical and temperature variations at that time,” he said.
Findings of a helium isotope he had seen in conjunction with ocean hot springs bolstered the theory that hot springs could be bubbling up through a crack ringing the lake bottom, producing heat and salts that stir up the lake.
A remote-controlled submersible made five dives in 1987. On one, Dymond and Collier saw what looked like a plume of smoke curling up from a crack, but they failed to get a temperature reading or a water sample for proof.
They returned last year for the first dives in Deep Rover. Navigation problems plagued them, and after 17 dives they were unable to claim more than encouraging evidence. This year, a system called ultra-short baseline acoustic navigation, which uses sound waves from four ground stations to locate the sub in three dimensions, cured the problems.
On Aug. 19, Collier piloted Deep Rover to a depth of 1,400 feet in the South Basin, where hydrothermal explorations were concentrated, and poked a probe into a bacterial mat, where it registered 61 degrees Fahrenheit.
Three days later, navigator James Cooley of Land and Sea Surveys peered into the colored plots on his computer screen and directed Dymond back to the area, where he found a temperature of 63.9 degrees Fahrenheit in another mat.
The temperatures met the U.S. Geological Survey test for a thermal spring--18 degrees higher than the mean annual air temperature at the surface, which is 37.8 degrees. The water at the lake bottom is 38.3 degrees.
“So it is a thermal spring in some sense,” said USGS engineer Manuel Nathenson in Menlo Park, Calif. Whether it is a “significant thermal feature” as required by law “is a judgment call by the secretary of the interior.”
California Energy geologist Joe LaFleur is skeptical and suggests that any flow at the lake bottom comes from cold mineral seeps. “Certainly an objective scientist would have to appreciate that nothing they have found would have any significant effect on the lake,” he said.
Although the bacteria mats suggest that something is flowing, Dymond and Collier could not see it or devise any way to measure it. They hope that other data will show some fluid seeping through bottom sediments.
One significant finding was made by Ray Weiss, a geochemist at the Scripps Institution of Oceanography at UC San Diego., whose team measured the amount of Freon in the water at the bottom of the lake, and found that it had been at the surface only three years earlier.
Nathenson said it appears that the lake is like a layer cake, with the top layer turning over like a normal lake in the spring and the fall, and a series of thinner layers mixing from one to the other to the bottom. In this way, oxygen works down from the top and heat and salts work up from the bottom.
