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October 8, 1998

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


Scientists explore Kilauea's underwater east rift zone

Scientists know more about the history and inner dynamics of Kilauea than they do about most other volcanoes in the world. Yet a major portion of the volcano has received little attention.

Starting at the shore of Cape Kumukahi, an underwater extension of Kilauea called the Puna Ridge stretches 75 km (45 miles) into the ocean and plunges to a depth of over 5,000 m (16,000 feet). By comparison, the distance from the summit of Kilauea to the shore is only 55 km (33 miles). The cones, craters, fissures, and lava flows along the surface of the Puna Ridge point to an active past. But because the ridge is so inaccessible, not much is known about it.

Some readers may have noticed a white ship cruising back and forth off Cape Kumukahi during the past week. The ship is the research vessel Thomas G. Thompson, owned by the University of Washington. On board is a diverse group of scientists embarked on a 36-day voyage, funded by the National Science Foundation, to make the first detailed study of the Puna Ridge. The team includes scientists from Woods Hole Oceanographic Institution, University of Hawai'i, Hawaiian Volcano Observatory, Bishop Museum, Smithsonian Institution, and elsewhere.

Scientists can learn a lot about the history and dynamics of a volcano by studying its shape and composition. For the first 20 days of the cruise, the scientists will create a detailed topographic map of the Puna Ridge. The tool they are using is an underwater vehicle equipped with side-scan sonar and tethered to the ship by a long cable. As the ship pulls the vehicle along the ridge, the sonar bounces sound waves off the surface. By analyzing the speed and intensity with which the sound waves return, researchers can create a vivid picture showing the location and size of volcanic features, such as craters, fissures, and lava-flow fields along the ridge. The vehicle also has an instrument to take magnetic readings of the ridge.

Once the scientists finish mapping the ridge, they will send down a second tethered underwater vehicle, the ARGO II, to photograph selected volcanic features. They may even lower the vehicle into one of the craters. In addition, they will collect rock samples from different points along the ridge and determine their chemical composition.

From this study, the team hopes to gain a better understanding of how magma moves through Kilauea. They are especially interested in how it travels all the way from the magma reservoir beneath Kilauea's summit into the Puna Ridge---a distance of 55-130 km (33-80 miles). This type of information is essential to improve existing interpretations about how Kilauea formed and now behaves. The new observations will help scientists assess how often submarine eruptions take place along the ridge---a valuable guide to the future. Large submarine eruptions, in fact, have been hypothesized to drain magma from Kilauea's summit and trigger explosive eruptions.

In addition, the shipboard team will examine how the extreme environmental conditions at great depth may affect lava flowing from the rift zone. This information can be applied to the study of other deep-water volcanoes.

The Puna Ridge is proof that much volcanic activity in Hawai'i takes place sight unseen, far beneath the surface of the sea. Our current ideas about Kilauea would doubtless be quite different if we could see, tromp around on, and measure its complete bulk rather than only that poking above the water. This cruise is designed to give us some of the information that we have been missing for so long.

Follow the adventures of the cruise on its web site, http://www.punaridge.org.

Eruption and Earthquake Update

There was no change in the eruptive activity at the Pu`u `O`o vent during the past week. Lava continues to flow through a network of tubes from the vent to the seacoast where it enters the ocean in two locations near Kamokuna. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

No earthquake was reported felt during the past week.

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Updated: 27 Oct 1998