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Volcanowatch

January 11, 2001

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


Eruption of Kilauea Volcano celebrates 18th birthday

If we had a dime for every time we've heard a visitor ask, "When is the volcano going to erupt?," we wouldn't be rich, but at least we could go out to dinner some place nice. As it is, we just sigh and launch into our usual explanation. The volcano is erupting, we say, but it's not the kind of eruption you were expecting.

For obvious reasons, TV stations and the tourist industry give heavy play to video footage and photographs from the early years of this eruption, when lava fountains as high as 460 m (1,500 ft) burst from Pu'u 'O'o every three to four weeks. In those days, people tried to time their trip to Hawai'i to see a fountaining episode, and many succeeded. The collective memory of those towering fountains refuses to fade, and, as a result, many visitors are surprised and a little disappointed to find out that Pu'u 'O'o got all that out of its system 14 years ago.

Episodic high fountaining lasted from June 1983 through June 1986, building a cinder-and-spatter cone 255 m high. 'A'a flows fanned out through native rain forest and soon overran several houses in Royal Gardens subdivision, a harbinger of things to come.

In the summer of 1986, the eruption shifted to a new site 3 km (1.8 mi) downrift. The new vent, named Kupaianaha, was the site of continuous eruption for the next 5.5 years.

The eruption changed its style as well as its location, becoming less exuberant with age. The spectacular lava fountains were replaced by steady effusion from a lava pond. Lava reached the ocean in November 1986, encased in lava tubes most of the way. Vog became an island issue as the continuous activity produced a pall of sulphurous air that has been with us ever since.

The section of Highway 130 that linked the coastal section of Hawai'i Volcanoes National Park with Pahoa was closed for good in early 1987. The community of Kapa'ahu, the park's visitor center at Waha'ula, and finally the village of Kalapana were overrun and buried by lava.

By early 1991, the output of Kupaianaha had begun a steady decline, as the magma dike linking Pu'u 'O'o and Kupaianaha began to constrict. In February 1992, Kupaianaha stopped erupting, and 11 days later, a fissure opened on the west flank of Pu'u 'O'o. This marked the beginning of an era of flank vent activity on the Pu'u 'O'o cone that continues today.

The eruption has deviated from Pu'u 'O'o only once since 1992, when fissures in and near Napau Crater erupted for about 22 hours in January 1997. Most of the time during the last seven years, the lava flowed to the shore within lava tubes and entered the ocean near the eastern boundary of Hawai'i Volcanoes National Park. Many archeological sites have been destroyed during this period, including Kamoamoa, Lae'apuki, and the remains of Waha'ula.

Until last spring, no houses had been overrun since late 1991. But in the last nine months, three long-abandoned structures in lower Royal Gardens were destroyed by the rising tide of pahoehoe on the coastal plain. The total area covered by lava since 1983 is 104 square kilometers (40 square miles), and the volume of lava has topped 2 cubic km (0.5 cubic miles).

So yes, Virginia, there is an eruption. The high fountains were extinguished back in 1986, but the show goes on. Lately we've been treated to the sight of streams of lava coursing down Pulama pali, because a brief pause in the eruption in mid-December caused the tube system to break down. As new lava tubes form, the surface flows will wane, and probably within a few weeks lava will be pouring into the sea again, somewhere between Kamokuna and Waha'ula.

A total of 3,173 earthquakes were large enough to locate in 2000. Forty of these were reported felt by Big Island residents. The largest earthquake of the year was felt islandwide on April 1 at 8:18 p.m. This earthquake had a magnitude of 5.0 and was located 10 km (7 mi) southeast of Kilauea's summit.

One earthquake was reported felt during the week ending on January 11. Residents in all districts on the island of Hawaii, except Kona, were shaken by an earthquake at 10:36 p.m. on Tuesday, January 9. The magnitude-4.0 earthquake was located 13 km (8 mi) southeast of the summit of Mauna Kea Volcano at a depth of 33.1 km (20 mi).


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Updated: January 17, 2001