Hawaii's "Gentle" Volcano More Dangerous Than Thought

Richard A. Lovett
for National Geographic News
May 6, 2009
Hawaii's tourist-friendly Kilauea volcano is famous for its lazy rivers of lava (Kilauea volcano lava pictures).

But a new report says the volcano, known as the world's most active, has a violent alter ego.

The coastal volcano on the Big Island of Hawaii is capable of much stronger eruptions than previously thought, according to the study.

"It turns out that the volcano—known for being this nice, gentle volcano [where] you can walk up to lava flows just wearing flip-flops—has a very dangerous side," said study co-author Tim Rose, a volcanologist at the National Museum of Natural History in Washington, D.C.

(Related: "Hawaii's Kilauea Lava Flow: 20 Years and Counting.")

Kilauea's violent side was revealed by a layer of tephra—volcanic ash and rocks—extending many miles from the volcano.

The tephra, the scientists determined, erupted some time between 1,000 and 1,600 years ago, when it apparently was blasted high enough into the air that today it would be a hazard to passenger jets.

"It threw golf ball-size rocks out to a distance of about 16 or 17 kilometers [10 to 11 miles]," said Donald Swanson, a volcanologist at the Hawaiian Volcano Observatory, who was also involved in the study, published in the May/June issue of the Geological Society of America Bulletin.

Related Video: Kilauea Eruption, July 2008

The tephra was found as far away as the coast—currently about 13 miles (21 kilometers), at its nearest point, from Kilauea's caldera—suggesting that the eruption might have spewed ash and rock even farther, out to sea.

Another round of eruptions, slightly less powerful, occurred between 500 and 200 years ago, Swanson added.

Buried Evidence

Kilauea's dark side wasn't recognized earlier because the old ash and rock deposits had been buried by more recent lava flows.

The telltale materials "didn't stand out," Swanson said. "You had to go searching for them."

If such an eruption occurred today, he added, it would blanket the summit in ash and rocks the size of basketballs.

But the scientists don't see an immanent hazard of a sudden repeat.

"There is certainly no indication that it's going to happen soon," Swanson said.

In fact, he said, volcanologists think Kilauea's crater would have to collapse inward before another such eruption would occur.

"We think the caldera has to be very deep for these big explosions to take place," Swanson said, "and right now it isn't."

More Volcanic Dr. Jekylls?

Other Big Island volcanoes may also have unknown violent sides, the researchers say.

"There are very large tephra deposits on Mauna Loa, the south flanks of Kilauea, and Mauna Kea," Rose said (Hawaii map showing volcanoes).

The sources of these deposits are currently unknown. But, he said, "some are incredibly thick and quite a long distance from the nearest possible source. There must have been some very large explosive eruptions."

© 1996-2008 National Geographic Society. All rights reserved.