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August 19, 1999

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Riding shotgun for a submarine

In the wild west of the 19th century, stagecoaches often had someone aboard whose job was to warn and protect the driver from marauding gangs and wild animals. This job, termed "riding shotgun," still exists but in various forms and degrees of sophistication.

Three weeks ago HVO rode shotgun for a research submarine visiting the active undersea volcano, Lo`ihi, south of Kilauea. The vessel, named the Shinkai 6500, is a state-of-the-art, three-person submersible capable of exploring the ocean to a depth of 6,500 m (21,300 ft). It is 9.5 m (31 ft) long, 2.7 m (8.9 ft) wide, 3.2 m (10.5 ft) high, and weighs 26 tons in air. The Shinkai 6500 is owned by the Japan Marine Science & Technology Center (JAMSTEC). It was brought to Hawaiian waters last month aboard its mother ship, the 4,439-ton Yokosuka, for scientific studies of the underwater Nu`uanu landslide north of O`ahu and Moloka`i, the deformed sea floor south of Kilauea, the east rift zone of Kilauea, and the edifice of Lo`ihi. The research agenda was decided by a combined American and Japanese team.

Hard questions were asked in Japan about diving on Lo`ihi. The JAMSTEC safety board originally nixed the idea, recalling the large 1996 earthquake swarm and eruption on Lo`ihi, which caused parts of the summit to collapse and which generated rock falls that would have been hazardous to anyone on the volcano at the time. And, the Shinkai 6500 is very expensive equipment that JAMSTEC doesn't want damaged. But much can be learned about the volcano and its hydrothermal emissions from submersible dives. In fact such dives have been carried out in the past by American vessels. The JAMSTEC safety board finally relented, agreeing to permit certain dives if a way could be found to warn the Yokosuka that an eruption was starting or that a seismic swarm was in progress.

Enter HVO. We were asked to provide a continuous watch on the seismic activity from Lo`ihi for the days that the submarine would be in the water. Unfortunately a sea-floor seismometer on Lo`ihi, operated by the University of Hawai`i, is not working, owing to a problem in the fiber-optic cable connecting it to the shore at Honu`apo. So, we arranged the next best thing--to have the seismic traces from the six island seismometers nearest Lo`ihi displayed on a terminal in the lobby. We then set up a duty schedule so that an HVO staff member would be monitoring the traces between 6:45 a.m. and 4:45 p.m. on the six days that dives were planned, including one weekend.

Using a satellite telephone, someone on the Yokosuka called us each morning before the submersible was placed in the water and each afternoon at the end of the dive. We would call the ship at any time during the dive if unusual seismicity were detected. Fortunately that never happened.

These observations were not always straightforward. The nearest three seismic stations, at Palima Point, South Point, and along the lower Great Crack, sometimes detected aftershocks of the magnitude 5.6 Pahala earthquake of April 16. The other stations, farther east in the Hilina fault system, detected small earthquakes there. We had to interpret quickly whether such earthquakes were from Lo`ihi, in which case we would call the Yokosuka to terminate the dive, or from the island, in which case we would do nothing. Fortunately, none was from Lo`ihi or the adjacent area.

The Shinkai 6500 returns to Lo`ihi in the middle of September after its stint on the Nu`uanu landslide. HVO will once again be riding shotgun for the submarine. We hope that Lo`ihi behaves itself then, too, for the dives are providing valuable information about Hawai`i's youngest volcano.

Eruption Update

The eruption of Kilauea Volcano continued unabated during the past week. Lava from Pu`u `O`o flows through a network of tubes to enter the ocean at the Kamokuna site in Hawaii Volcanoes National Park. On August 18, the entire active lava bench at the ocean entry collapsed into the sea. Portions of the sea cliff west of the bench also collapsed. The public is reminded that the ocean-entry area is extremely hazardous, with explosions accompanying unpredictable collapses of the new land. The steam clouds are highly acidic and laced with glass particles.

An earthquake at 2:05 p.m. on August 16 was widely felt across Ka`u. The magnitude-4.4 earthquake was located located 9 km (5.6 mi) north of Pahala at a depth of 9.8 km (6 mi).

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Updated: 2 Sep 1999