The Island of Hawaii is made up of five volcanoes. Each began to grow beneath the sea and eventually joined to form a single island. The volcanoes grew from a hotspot beneath the sea. The chain of volcanoes were created as the Pacific Plate moved northwestward over the hotspot. Kohala was the first to emerge from the sea followed by Mauna Kea, Mauna Loa, Kilauea, and Loihi. Activity has ceased at Kohala and now the most activity has been occuring at Kilauea and Loihi.

Loihi is still beneath sea level about 20 miles off the southeast flank of the island. Presently a scientific team is laying underwater cable to Loihi. On October 12, the cable was laid and scientists discovered that Loihi appears to be in full eruption. The communication cable will provide a direct connection to Loihi. In the past, instrument experiments had to be dropped off at the seamount and later physically picked up by a submersible research vessel to recover the data.

Scientists are already getting results from the cable. An underwater microphone called a hydrophone is sending back sounds of popping, booming and crashing. If Loihi is erupting this may be the first real-time monitoring of an undersea eruption. In the next several weeks scientists will link up a communication system to carry data first to the Hawaiian Volcano Observatory and then to Oahu where it will be available for researchers.

At Hawaii Volcanoes National Park visitors have the opportunity to see Kilauea in action. I took a trip to Kilauea yesterday. As I drove past the giant Kilauea crater I noticed many active steam vents. I followed Chain of Craters Road past many craters, recent lava flows and ancient petroglyphs to where the lava has forced closure of the road. I hiked out across the a'a and pahoehoe lava to where the hot lava from the current eruption from Pu'u O'o pours into the ocean. It was an amazing sight. As the lava entered huge plumes of steam and cloud exploded upwards. Many people may think that a visit to the volcano means they will see huge fire fountains shooting out of the top of a mountain cone. This is not the case with Kilauea where lava flows to the ocean through underground tubes with an occasional skylight. The summit is a rolling plateau surrounding a cliff-bounded depression called a caldera.

The caldera is two to three miles across and about 400 feet deep on its north side. This was caused by a violent collapse accompanied by great earthquakes and rockfalls as the caldera floor dropped hundreds of feet in a time span from days to weeks. At Kilauea there have been many episodes of rapid caldera collapse followed by centuries of refilling.

Geologists believe that a collapse happens when submarine eruptions tap off major volumes of molten magma from a reservoir 2 to 4 miles below the caldera. When the magma is removed, the summit of the volcano cannot support its own weight and crashes into the emptiness below.

The last major episode of collpase occurred in 1790 and was accompanied by a giant explosion. Since 1790 Kilauea's eruptions have been mostly quiet lava flow. Hawaii is one of the few places in the world where eruptions can be viewed at close range with little danger. Still, young children, pregnant women and people with breathing problems must take care around volcanic fumes!

Sometimes Kilauea's eruptions occur at the summit, other times they occur along the rift zones that extend down the east and southwest flanks of the volcano to the ocean and across some miles out on the seafloor. The rift zones are regions in the flanks of Kilauea where large vertical cracks split open the volcanoes sides for miles. Geologists believe these fractures are forced open by the pressure of magma accumulating in the underground reservoir. Lava flows from the eruptions at the summit are slowly filling the great caldera pit; flows from flank eruptions pour down the slopes from the rift zones and sometimes reach the sea, adding new land to the island. Kilauea has been built up by hundreds of thousands of lava flows. This type of volcano is known as a shield volcano because in profile the gentle slopes resemble a warrior's shield.

Sources of information from: Loihi Apparently Erupting - Dave Smith
Hawaii Tribune-Herald, October 13, 1997

U.S. Department of the Interior
U.S. Geological Survey
Geologic Map of the Island of Hawaii
Compiled by Edward W. Wolfe and Jean Morris

Road Guide to hawaii Volcanoes National Park
Barbara and Robert Decker
Double Decker Press, Mariposa California, 1992

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