SCIENTISTS BAFFLED BY BOILING LAKE THAT ISN'T

by Mark, Sunday, April 24, 2005, 09:33

"More Signs of the times!"

LAUDAT, Dominica â€" Boiling Lake, this Caribbean island's most exotic tourist lure, has ceased to simmer.

For nearly four months, the volcanic crater's usually bubbling brew has been calm, except for brief surges when water inexplicably drains away, then rises again. The temperature rises and falls, sometimes hot enough to send up steam clouds, other times so tepid that adventurous visitors have dared to swim in it. The color has varied from gray-green to alabaster, and, most recently, black as coal.

The mysterious changes have scientists scratching their heads and hikers skipping the seven-hour round-trip trek that many found adventurous enough without added risks.

"The lake has stopped boiling at times in the past, but what worries us about this case is that the changes are drastic and really, really fast," said Nicolas Fournier, a volcanologist with the Seismic Research Unit of the University of the West Indies in Trinidad and Tobago.

The 200-foot-wide lake is a crater filled by underground rivulets and rainwater and heated by volcanic gases.

Since the boiling stopped in late December, the water level has fluctuated, dropping as much as 40 feet, leaving a sludgy pool of gray sediment on the bottom and a ring of mineral residue. Water normally so hot that it can cook an egg in five minutes cooled to a tepid 68 degrees in January, when a party of Austrian hikers ventured in.

Boiling Lake has baffled Dominicans before. In 1887, 1900, 1971 and 1988, the lake water calmed and drained away through the fumaroles that funnel heat from beneath the crusted lava lake bed. But each time, the water level and temperature returned to normal within a few weeks.

Fournier speculates that a magnitude 6.3 earthquake north of Dominica on Nov. 21 caused the thick mineral sediment on the lake floor to shift and clog the fissures from which volcanic heat had been reaching the water.

But he is at a loss to explain why the water level has been fluctuating so dramatically.

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"People are really baffled by what the lake is doing now. It seems able to empty and refill itself very quickly," James said. During an April 13 visit, the lake was nearly full and its water black from what he suspects was iron sulfide. The water temperature was up to 138 degrees, twice as warm as it had been a month earlier yet far below its usual 197 degrees.

James said he has noticed a drop in the hiking traffic since the boiling ceased. On one recent weekday, the trail was empty.

"People are tentative about going down there now," he said of the rugged route from Laudat that takes hikers through rain forest, along narrow ridges, up steep rocky inclines and through the aptly named Valley of Desolation.

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In 1900, when the lake stopped boiling for a month, a Dominican guide and two tourists were peering into the nearly drained crater when a sudden belch of sulfurous gas issued from beneath the water. The guide and one of his charges were knocked unconscious by the fumes and fell to their deaths, Fournier said.

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Fournier said there was a risk of "phreatic eruption," or blasts of steam and gas, but noted that if molten lava was trying to force itself to the surface, the water temperature would be rising faster.

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"The recommendation is for people not to get too close and not to linger," said Fournier, who will be leading a seismologists' trek to the lake in May.

"They should get in, get their look, then get out of there. And obviously they should not go swimming!"