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December 31, 1998

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


Eruption of Kilauea Volcano continues into its 17th year

Today is the 16th anniversary of the ongoing Pu`u `O`o-Kupaianaha eruption of Kilauea Volcano. Lava has erupted from vents located on Kilauea's east rift zone since January 3, 1983.

Most of the time, lava flows continuously from a vent through a network of tubes to the ocean. Occasionally, this flow is interrupted by intrusive events either at the summit or at the east rift zone. These events often lead to eruptive surges and new surface flows, and occasionally to changes at the vent. Flow from the vent ceases for a few hours to a few months as the magma system recharges. Since 1992, the largest of these events have occurred in late January or early February.

In early February 1992, an 11-day-long pause in the eruption followed the demise of the destructive Kupaianaha vent and the return of the eruption to the Pu`u `O`o vent after 5.5 years.

On February 7, 1993, a 9.5-day-long pause followed the intrusion of a dike into the east rift zone.

On February 1, 1996, an eruption surge was followed by a 10-day-long pause, the longest since 1992. The surge began with a swarm of small shallow summit earthquakes, followed by tremor and a rapid pressurization of the magma chamber. This continued for a few hours, then abruptly reversed when magma surged from the summit to the east rift zone, where it gushed out of several skylights forming dome fountains. These dome fountains fed fast-moving channeled a`a flows.

On January 30, 1997, a 23-day-long pause followed the intrusion of a dike uprift of Pu`u `O`o and a one-day-long eruption from fissures in Napau Crater. This dike intrusion drained the lava pond at Pu`u `O`o, which did not reappear until February 24. The outbreak of surface flows on March 23 ended the longest period without flowing lava since 1986.

On January 14, 1998, an eruption surge was followed by a short pause and a couple weeks of unsettled behavior. This was a smaller version of the February 1, 1996 event. Although there were many other pauses in 1998, four of them lasting longer, this was the most dramatic event.

What will the new year bring? We do not know whether there will be some type of intrusive event in early 1999, but we remain watchful. In the last decade, by coincidence or from some yet unexplained cause, the largest of these events have occurred in late January and early February. In any case, the longest-lived eruption from Kilauea Volcano's east rift zone in recorded history continues into its 17th year, with no end in sight.

Eruption Update

As we enter the 17th year of nearly continuous eruption, there is no change in the activity of Kilauea Volcano. Lava continues to erupt from Pu`u `O`o and flow through a network of tubes from the vent to the sea near Kamokuna. The flow of lava through the tubes stopped on 11 occasions in 1998. The pauses lasted from 11 hours to as long as 53 hours. The volume of lava measured flowing through the tubes varied from 1.5 cubic meters per second (17.5 cubic ft/sec) to 11.0 cubic meters per second (130 cubic ft/sec). The average volume was about 4.5 cubic meters per second (53 cubic ft/sec). This converts to a daily average volume of 400,000 cubic meters (4,700,000 cubic feet). No structures were destroyed in 1998.

The deterioration of air quality in Hilo during the past week is due to a shift in wind direction and not from a change in the eruption. Kona winds are more frequent during the winter months, and they carry the volcanic gases into populated areas that are usually upwind of the vents. The volume of sulfur dioxide (the main component of 'vog') emitted from Kilauea Volcano in 1998 fluctuated from 1,300 metric tons per day to 4,000 metric tons per day. The average volume measured was about 2,340 tonnes per day.

Three earthquakes were reported felt during the past week, ending on December 31. Residents of Leilani Estates reported two tremors at 11:26 a.m. and 11:29 a.m. on Sunday, December 27. Both earthquakes originated at a shallow depth near Puulena crater. The earthquakes had magnitudes of 3.1 and 3.2, respectively. At 1:57 p.m. on Monday, December 28, residents of Hamakua, Hilo, and Puna were jolted by a magnitude-3.7 earthquake. The earthquake was located 14 km (8.5 mi) west of Honomu at a depth of 24.3 km (14.6 mi).

A total of 95 earthquakes were reported felt during 1998. The largest earthquake of the year occurred 11 minutes after midnight on June 27 and had a magnitude of 5.0. The epicenter of this earthquake was 53.3 km (32 mi) west of Kawaihae at a depth of 52 km (31.2 mi). The earthquake was felt by residents of Maui and Hawaii. The next largest temblor, a magitude-4.8 earthquake from the south flank of Kilauea at 8:39 p.m. on September 28, caused minor damage in Hilo and Puna. The staff of the U.S. Geological Survey's Hawaiian Volcano Observatory located more than 4,800 earthquakes in 1998. We appreciate your cooperation in submitting felt reports to us at 967-7328. Have a happy and safe 1999.

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Updated: 7 Jan 1999