Saturday, May 12, 2001


A view of the 1950 Mauna Loa eruption as the lava flows met the ocean.

Mauna Loa
dormant but still
poses a threat

An eruption from the Big Isle
volcano in '84 sent a lava flow
to within 4 miles of Hilo

U.S. Geological Survey
Hawaiian Volcano Observatory

ON THE NIGHT of June 1, 1950, after many residents of Hookena-mauka village in South Kona had already gone to bed, Mauna Loa began to erupt.

Soon the roar of the lava fountains could be heard from Highway 11, 15 miles away, as molten lava poured from fissures high on the volcano's southwest rift zone. In only three hours a flow reached the highway and invaded the village. The streets were lit by flames as lava consumed several houses and the post office.

Thirty-five minutes later, the flow entered the ocean.


The Star-Bulletin introduces "Volcano Watch," a weekly column written by scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory. The writers will address the science and history of volcanos in Hawaii and elsewhere. It also will include a short, separate update on eruption activity on the Big Island.

By daybreak, lava flows had crossed Highway 11 in two places, cutting off the only escape route. The villagers had all reached safety unharmed, but for some it had been a close call.

Mauna Loa has erupted twice since 1950, with a one-day outbreak at the summit in 1975 and a three-week eruption on the northeast rift zone in April 1984.

Most of Mauna Loa's eruptions in the last 150 years began at vents near the summit. About half of these summit eruptions quickly developed into flank eruptions along one of two rift zones that extend down its northeast and southwest slopes. A few eruptions have also originated at isolated vents on the volcano's northern slope.

The 1984 eruption followed the typical pattern, beginning at the summit and quickly migrating down the northeast rift zone. Lava flows came within four miles of the outskirts of Hilo before the eruption ended.

This eruption covered 16 square miles of land with lava in just three weeks, whereas the ongoing eruption of Kilauea that began in 1983 took three years to cover a comparable area. Fortunately, most of the property buried by lava in 1984 was uninhabited land owned by the state.

Eruptions on the southwest rift zone present a much greater threat to life and property. The slopes are steep, and residential areas extend from Highway 11 right up to the rift zone. Although the population has increased greatly since 1950, the two-lane highway remains the only escape route.

The good news is that the ability to monitor, and possibly forecast, the next eruption of Mauna Loa has been greatly enhanced by better instrumentation. Since 1984 the Hawaiian Volcano Observatory installed two more seismometers on the southwest rift zone.

In the summer of 2000, three dilatometers -- instruments that measure expansion and compression -- were cemented into bore-holes 425 feet deep on Mauna Loa's flanks.

From 1975 through 1983, measurements of ground deformation near Mauna Loa's summit indicated slow but persistent inflation. For more than a year prior to the 1984 eruption, the number of earthquakes beneath the summit of Mauna Loa gradually increased.

If Mauna Loa follows a similar pattern of deformation and seismicity before the next eruption, we will have a year or so of warning.

Since the rate of inflation has slowed considerably over the past several years and the seismicity has not increased, we do not think that the next Mauna Loa eruption is right around the corner.

But that does not mean we can forget about it. It means that if we act now, residents and county officials still have time to prepare for the inevitable.

This article was written by scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory. Contact the observatory at P.O. Box 51, Hawaii National Park, HI 96718; or call (808) 967-7328.


Kilauea lava reaches the sea near Kupapau

Eruptive activity of Kilauea volcano continued unabated at the Puu Oo vent during the past week.

Breakouts from the tube system occur above Pulama pali and feed multiple flows that are usually tubed over as they descend Pulama pali.

Surface flows are seen throughout the coastal flats, and the most active area has been beyond the eastern boundary of Hawaii Volcanoes National Park near Kapaahu. Lava entered the ocean on May 5 in an area east of Kupapau. As of May 10, lava was entering the ocean at three separate locations, spanning about 1,500 feet of shoreline.

One earthquake was reported during the week ending Thursday. Residents of South Kohala felt an earthquake at 4:33 a.m. Wednesday. The magnitude-3.5 earthquake was located 8.4 miles southwest of Kawaihae at a depth of 12.6 miles.

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