Ocean drillers off O'ahu find traces of slide
By Jan TenBruggencate
Advertiser Science Writer
Hawaiian volcanoes have a reputation for being of the nonexplosive variety, but a deep-ocean drilling project off O'ahu suggests that there was at least one massive, catastrophic eruption there — and that there could be another on the Big Island.
Hawaiian Volcano Observatory scientists said they have doubts about the announcement from the multinational Ocean Drill-ing Program, which reported its finding yesterday. There may be alternative interpretations of the data found by the drilling program, and the conditions that may have led to past explosions may not exist at other Hawai'i sites today, the scientists said.
The drilling program is on a global mission of drilling deep into the ocean floor and using the resulting cores of rock to learn about the Earth's geologic processes. In December, it drilled off O'ahu in its 200th drilling leg.
Co-chief scientist Ralph Stephen announced that the project found evidence of a "cataclysmic volcanic event" 2 million years ago that was much larger than the 1980 explosion of Mount Saint Helens in Washington. He and his colleagues said it was associated with a vast landslide in which an entire section of O'ahu collapsed into the sea.
Stephen said the scientists with the Joint Oceanographic Institutions of Washington, D.C., which runs the Ocean Drilling Program, based their conclusions in part on finding layers of rock that appeared to have been very hot when they were exploded out into the ocean.
"I want to see the data before I believe that," said Hawaiian Volcano Observatory geophysicist Peter Cervelli, an expert in undersea slides. "What he describes is pretty fantastic in terms of Hawaiian volcanism. I guarantee there are other interpretations."
Geologists have long known there are giant slides off the Hawaiian Islands. Steep volcanic slopes can suddenly slip, sending rubble rolling along the ocean floor for miles out to sea. Among the biggest such slides are the ones that collapsed the north side of Moloka'i and the Nu'uanu slide, which took down the northeastern side of O'ahu.
"Our drilling results from Leg 200 indicate that this event was not merely a landslide, but a hot explosion," Stephen said. He suggests the slide was so huge that it allowed magma, which had been held deep underground by the land, to explode into the air and the sea.
The same thing could happen again on the Big Island, Stephen said.
Don Swanson, chief scientist at the Hawaiian Volcano Observatory, said he questions the extension of the drilling results to a threat to the island of Hawai'i, but he said he does not doubt that a large slide could expose hot rock.
"The landslides can cut pretty deep into a volcano," he said.
That does not necessarily mean there would be a huge explosion, Swanson said. He said there may be other processes that could provide the evidence the drilling project scientists used to come to their conclusions.
"The statement that the same process could happen again on the Big Island, there is no evidence that it could," Swanson said.
The Associated Press contributed to this report.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
