Experts Keep Cautious Watch on Alaska’s Twin Water-Filled Volcanoes : Geology: An eruption could disrupt air traffic and alter the Becharof Wildlife Refuge.

An Alaska Peninsula moonscape pocked by a pair of stubby volcanoes keeps drawing Ronald Hood to the rim of one of the craters.

He likes to look down at what used to be topsoil, now layered in lava.

“You can still see an old cottonwood,” said Hood, manager of the vast Becharof Wildlife Refuge, which surrounds the twin volcanoes. “I go out there every chance I get.”

Experts say the craters, products of a 26-year-old eruption about 325 miles southwest of Anchorage, are the world’s youngest water-dependent volcanoes.

Known as “maar” volcanoes, from the Latin “mare” meaning “sea,” the twin craters formed during an 11-day explosion when magma boiled to the surface, hit shallow water and shot up a cloud of steam, ash and rock.

“We need to understand just how big a hazard they pose,” said Tina Neal, a geologist with the Alaska Volcano Observatory. “We’re always concerned that a sudden explosion could interfere with air traffic.”

Scientists from Alaska and Northern Arizona University recently ended two weeks of field work, lowering themselves into the larger volcano to observe old tree stumps and roots and chip rock from each layer of the wall. They also dug nine feet into ash debris to collect samples.

“Worldwide, these are a pretty common feature,” said Neal, who helped collect and analyze rock from the volcanoes.

“What’s exciting is we don’t understand them well,” she said. “They’re low-relief--not like Mt. Fuji or St. Helens. So many of these volcanoes are filled with water that we stumble upon them very late.”

The twin volcanoes sit atop a 300-foot ridge on the south shore of glacier-fed Becharof Lake. Scientists named the twins “Ukinrek,” for “two holes in the ground” in Yu’pik Eskimo.

The explosion in 1977 blew ash to 20,000 feet and attracted photographers who flew overhead. The eruption, visible 75 miles away, killed no one.

Neal said the Ukinrek are widely regarded as the world’s newest maar volcanoes. Others are found in Hawaii, Africa and on the Seward Peninsula in western Alaska. Most maar volcanoes erupt only once.

The team will try to reconstruct how the crater built up by matching rock samples with old weather data and photos.

A study of wind patterns, for instance, could help account for the wall’s thick spots. Researchers will even look for signs of old snow.

“We know, for instance, that it snowed April 4, while the eruption was ongoing,” Neal said. “When the snow melted it would have caused the wall’s layers to deform and crinkle and look chaotic. We can recognize those clues.”

The March 30, 1977, explosion produced a small elliptical crater, about 500 feet across and 100 feet deep. The crater today is filled with a few inches of water.

A second blast lasted more than a week and bored the larger crater, 1,000 feet across and filled with water 150 feet deep. The two craters are about 1,000 feet apart and near Mt. Peulik, a 4,800-foot volcano that last erupted in the early 1800s.

Studies of the lava’s chemistry show Peulik and the Ukinrek were unrelated events. The volcanoes do not share a magma network.

Researchers hurried to the site in 1977 to see the maar volcanoes and leave behind gear to gauge earthquakes associated with eruptions. The current project, funded by the National Science Foundation, is an attempt to update data with new technology, to understand how magma and water mix.

The Becharof refuge south of Katmai National Park is best known for fishing and trophy bear hunts. Bears lumber up Peulik’s snowy flanks to escape August heat or wander into the small crater. Caribou are attracted to the ridge as a lookout.

Hood predicts an influx of rock hounds, too, eager for a glimpse of the maar volcanoes which are part of the Pacific’s ring of fire.

“This place is just full of unique surprises,” he said.