By Ken Sakamoto, Star-Bulletin
University of Hawaii scientists Julia Morgan and
Gregory Moore embark on a cruise next month to
research Kilauea's landslide.

UH scientists
to examine Kilauea
undersea landslide

Learning how volcanoes
grow and fall apart may offer
clues to the future

By Helen Altonn

Could the Big Island end up like Oahu, with big chunks of it spread across the sea floor?

University of Hawaii scientists Gregory Moore and Julia Morgan hope to begin answering that question next month.

Using Columbia University's ship R.V. Maurice Ewing on a three-week cruise beginning Jan. 26, they will generate earthquakes near the ocean surface off the Big Island. A 2-1/2-mile cable will be towed with 160 hydrophones to collect data.

Their goal: to try to understand the deep internal structure of Kilauea's thick landslide and the way volcanoes are growing and falling apart.

They will also investigate the ocean floor northeast of Oahu where giant blocks -- up to 20 miles across -- remain from an Oahu landslide. A debris avalanche tumbled part of Oahu along the Nuuanu Pali into the sea more than one million years ago, the scientists said.

Moore, a geologist-geophysicist, and Morgan, a geologist, want to compare the slow-moving Hilina slump on Kilauea to the ancient Oahu landslide -- believed to be the largest on Earth. The Tuscaloosa seamount is the largest remnant of the Oahu slide in a debris field extending about 14,260 square miles.

From geodetic work on land and offshore topography, it's known that Kilauea's whole south flank is moving seaward and down, Moore said.

He said earthquakes define approximately where the slide's base is beneath Kilauea. But they can't tell anything about the slide's geometry seaward of the shoreline, he said. "So we're trying to see what the extent of the current slump is offshore. We don't know if it's 100 feet thick or a couple miles thick."

If it's fairly deep, Morgan said, it could slide in tiny little steps or jerky adjustments similar to 1975 when a section of Hilina Pali suddenly dropped into the ocean. It caused a 7.2 magnitude earthquake and a 48-foot tsunami.

A shallower surface could be related to a catastrophic debris avalanche and fail very rapidly, such as happened long ago on Oahu, she said.

Moore cited one idea to explain the Kilauea slide: Lava welling up pushes apart but can't go anywhere on one side because the flank is leaning against Mauna Kea. The other side is free so the lava can slide off into the ocean.

The sliding is believed responsible for Kilauea's slow creep into the ocean, and it may be related to earthquake and major slip events, Morgan said. But the flank's movement may be different from the motion of the landslide, she said. "We could have two phenomenon. We don't know, except from seismic data."

Courtesy J.R. Smith, © University of Hawaii

U.S. Geological Survey geologist James G. Moore said in 1964 that giant landslides may have helped to shape the Hawaiian Islands but nobody believed him, Gregory Moore said. "The most vocal opposition to that idea came from UH."

Evidence came in the late 1980s and early 1990s when surveys showed lots of slumps and debris avalanches around the islands, the UH scientists said.

In a telephone interview from his office in Menlo Park, Calif., James Moore said the Tuscaloosa Seamount has moved at least 50 miles "and we think it moved rapidly." It is at least 15 miles long and about a mile high, he said.

"It's an important study -- a long time in coming," Morgan said. "It should have a lot of implication for how we interpret the growth of these islands and the hazards of living on these islands."

Whether it's something to worry about now is another question.

Such processes operate on a geologic time scale, Gregory Moore pointed out. "An event that would cause a major catastrophic failure could happen 10,000 years from now."

But if Kilauea's flanks are unstable, the scientists said they want to know now. The Geological Survey speculates that a big landslide can cause a giant tsunami, although it's "a very controversial hypothesis," Morgan said.

The ship will move about 5 mph along 20 miles of coastline generating "earthquakes," Moore explained.

The ship will tow 20 large chambers with high pressure air lines connected to air compressors on the ship. They'll be pumped continually full of air and the pressure released about every 165 feet. Data will be collected as the sound energy goes below the sea floor and bounces to the surface.

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