February 2, 1996

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

Kilauea Summit Eruption Coming?

On Thursday morning, February 1, Kilauea Volcano had an intense swarm of small, shallow earthquakes and rapid ground deformation at the summit. This type of activity with as many as six earthquakes a minute, commonly precedes eruptions. The U.S. Geological Survey's Hawaiian Volcano Observatory staff prepared for a possible summit eruption. The earthquake activity died out after about four hours, and the ground deformation reversed from inflation to deflation. The summit eruption never took place.

This was an unusual event in that the summit rapidly inflated, commencing about 15 minutes after the first seismic activity, and then almost as rapidly subsided to nearly the same state it began. The last two similar events led to a summit eruption in 1982, and an intrusion into the upper East Rift Zone in 1990. This time, lava came close to erupting, as seen by the shallow depth of the earthquakes, the occurrence of rock bursts in Halemaumau, and by a change in the relative concentrations of carbon dioxide and sulfur dioxide at fumaroles near Halemaumau.

The ongoing eruption on Kilauea's East Rift Zone at Pu'u 'O'o continued throughout the seismic crisis and then intensified as the seismic crisis at the summit waned. The volume of lava issued at the eruptive vents near Pu'u O'o increased by at least a factor of three after the earthquakes died out. The volume was so great that the tube system to the sea could not contain it all. Lava welled up and out of the top of the tube at numerous locations.

The largest and most vigorous of these breakouts had lava doming up to 35 feet above ground level and feeding rapidly advancing surface flows. This high-volume phase lasted through the rest of the day, but the output decreased by Friday morning.

Late Thursday night, lava stopped entering the ocean through the old tube. On Friday, all activity consisted of surface flows along most of the flow field. Shortly after noon on Friday, lava again reached the ocean, in roughly the same place as last observed. This indicated that the old lava tube was reoccupied.

The huge lava eruptive rate on February 1 was accompanied by an equally large emission of volcanic gases. By Friday morning, these gases had accumulated due to the low and variable wind conditions. This produced heavy vog over much of the eastern half of the Big Island.

We measured sulfur dioxide concentrations exceeding 4 parts per million at the Observatory early Friday morning. Such levels are about twice the highest readings we have made at HVO, and exceed the EPA health standards for sulfur dioxide. Fortunately, as the day wore on, the winds picked up and dispersed these severe concentrations of gas and reduced the health hazards they posed.

By Friday afternoon, activity at Kilauea had stabilized at nearly the same levels as before this large "hiccup" in the magma system. Such events indicate that no matter how steady the activity may seem, dramatic changes can occur rapidly and without warning.

This seismic crisis and ensuing increase in eruptive activity served to demonstrate the close cooperation between the U.S. Geological Survey and other government agencies. We promptly alerted Hawaii Volcanoes National Park officials of the unstable Kilauea summit situation. They then closed sections of the park to ensure the safety of their visitors. Hawaii County and State Civil Defense agencies were also notified immediately, and they contacted other agencies in turn. The Federal Aviation Administration closed air space above the park to protect aircraft from potentially flying into a volcanic ash cloud. Hawaii County Police prepared for increased traffic on the highway leading to the park. The last summit eruption caused a major traffic jam when thousands of visitors entered the park. As the situation changed, all agencies were apprised of the developments.

The swarm of shallow earthquakes elated a group of visiting seismologists conducting a month-long experiment on Kilauea Volcano. This will be discussed in the column next week.