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The Honolulu Advertiser
Posted on: Monday, December 18, 2006

Kilauea's swelling seems over

By Kevin Dayton
Advertiser Big Island Bureau

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HILO, Hawai'i An unprecedented three-year swelling of Kilauea volcano seems to have ended, at least for now, scientists say.

Instruments monitoring the volcano show the dramatic uplift at the Kilauea summit and the volcano's east and southwest rift zones ceased in early October, a sign that the supply of magma flowing into the volcano may have leveled off.

Experts aren't sure why. Some suggest the halt in the swelling may have been caused by the Oct. 15 earthquakes off the west coast of the Big Island, but Hawai'i Volcanoes Observatory geophysicist Michael Poland said the timing probably was a coincidence.

The swelling at the summit and rift zones apparently stopped about a week before the earthquakes, which suggests the inflation of the past three years may have been caused by a "pulse" of extra magma that played out on its own, he said.

"Of course, it may not have petered out, this may be a minor lull, and we may see resumed inflation tomorrow, but for now we've had a two-month period of no inflation of the summit," he said.

For most of the continuing Kilauea eruption that began in 1983, the summit has been deflating as lava poured from the volcano "like air being let out of a balloon," Poland said.

There were only three periods during the eruption where the volcano began to inflate again, and in two of those cases, the swelling signaled major changes.

The surface of the volcano began to move up shortly before the eruption shifted from Pu'u 'O'o vent to Kupaianaha vent in 1986, and again before the eruption shifted back to Pu'u 'O'o in 1992.

In both cases, the flow of lava out of the vents in the East Rift Zone slackened as the volcano swelled, perhaps because the magma was obstructed.

In the third and longest period of inflation, which just ended, the volcano swelled for three years.

This time, the swelling was accompanied by steady or increasing lava flows out of the Pu'u 'O'o vent, according to an abstract of a paper co-written by Poland, Asta Miklius and other researchers that was presented Thursday at the fall meeting of the American Geophysical Union in San Francisco.

The swelling was most dramatic over the past year, when the ground at the summit rose about a foot, Poland said.

In April the southwest rift zone of the volcano also began to inflate, which scientists interpreted as a sign that the magma flowing into the summit was being forced into that rift area, which hasn't had an eruption since 1974.

Until the swelling stopped in October, there probably was more magma being supplied to the volcano this year than had flowed into Kilauea for at least the past 20 years, Poland said.

"You can imagine that the volcano can only take so much, and at some point, something would have had to give, whether it would have been an eruption in the southwest rift or perhaps an increase in the eruption rate out of Pu'u 'O'o, or something happening at the summit. It's difficult to know," he said.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.