Posted on: Monday, October 29, 2001

'Nearly extinct' volcanoes studied

By Timothy Hurley
Advertiser Maui County Bureau

New research shows that volcanic eruptions occurred in West Maui long after the growth stage of its volcano, a finding that adds to a growing body of evidence that indicates "nearly extinct'' volcanoes on O'ahu, Moloka'i and Maui could erupt again.

"We wish it wasn't true, but it is,'' said Don Swanson, scientist-in-charge at the Hawaiian Volcano Observatory in Hilo.

While the researcher who conducted the study said there could be some real problems created by a "rejuvenated-stage'' eruption in developed areas, he said the hazard is virtually nil because of the relatively small size of the lava flows — generally a few acres in these late events — and the fact that technology would allow at least a month's warning.

Not to mention that hundreds and thousands of years often pass before such eruptions strike.

"It's pointless to worry about it,'' said David Sherrod, a Hawaiian Volcano Observatory geologist.

Sherrod collaborated with Yoshitomo Nishimitsu of Kyoto University to determine the radiometric ages of lava flows around the West Maui Mountains. The scientists discovered that the four youngest vents around West Maui erupted between 610,000 and 385,000 years ago.

Scientists commonly use the phrase "rejuvenated stage'' for eruptions that occur long after a Hawaiian volcano has finished its main stages of growth.

West Maui ended its growth by about 1.1 million years ago, and nearly 500,000 years passed with no evidence of renewed activity, Sherrod said.

But the volcano wasn't quite finished.

Later eruptions were all from small cinder cones that grew relatively briefly and then died. Lava flows spewed from each, Sherrod said, but the area covered by lava was generally only a few acres, although one spread over hundreds of acres.

The oldest of the four cones is Kilea, located inland from Olowalu on the southwest side of West Maui. Known today for its petroglyphs, Kilea erupted about 610,000 years ago.

Active at nearly the same time was Keka'a Point, site of the Ka'anapali Resort. Lava from Keka'a has an age of 580,000 years.

About 200,000 years passed before a West Maui site blew again. This time Pu'ulaina, a cinder cone north of Lahaina town, spread lava over 800 acres, the largest of the young flows.

At about the same time — 385,000 years ago — a fourth cone, Pu'uhele, erupted about a mile and a half north of Ma'alaea, near where the Honoapi'ilani Highway is today. Pu'uhele was quarried so extensively that the mound of the cone is gone.

The dates of the West Maui eruptions, occurring long after the volcano's growth stages, build on previous evidence that indicates Hawai'i's rejuvenated-stage volcanoes could erupt again, Sherrod said.

That means volcanic activity could be in the future for the Ko'olau Volcano on O'ahu. Diamond Head, Punch Bowl and Koko Head are examples of eruptions created from Ko'olau well past its growth stages, he said.

On Moloka'i, an eruption is possible from the East Moloka'i Volcano, which last erupted to create the Kalaupapa Peninsula.