Volcano Watch — Kīlauea: The longest and most destructive eruption

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Editor's note: Today's "Volcano Watch" includes the first half of a 11-year retrospective of the Kīlauea eruption up to October 1992. Next week, the second half will cover the most recent volcanic action at Kīlauea.

Editor's note: Today's "Volcano Watch" includes the first half of a 11-year retrospective of the Kīlauea eruption up to October 1992. Next week, the second half will cover the most recent volcanic action at Kīlauea.

The First Eleven Years

The Pu‘u ‘O‘o-Kupaianaha eruption now ranks as the longest-lived historic eruption on the East Rift Zone and the most destructive in Kīlauea's recent history. Monday marked the 11th anniversary of the beginning of the eruption. Lava flows have destroyed 181 houses and severed the coastal highway along the volcano's south flank, severely restricting transportation on this part of the island. The eruption consisted of many distinct episodes characterized by activity at different vents and by different eruptive styles. The following summarzies the first 11 years of the eruption, starting with the initial outbreak in January 1983.

Episodes 1-3: Initial Fissure

The eruption began early on January 3, 1983, and, over the next four days, a discontinuous series of fissuresopened along a five-mile long section in the middle of Kīlauea's East Rift Zone about 10 miles from the volcano's summit. Lava fountains became localized along a 0.6-mile-long section of the fissure, where activity continued intermittently for several weeks. The next episode began on February 10 with low-level activity at a new vent, called the 1123-vent for the time of initial activity, and culminated with vigorous fountaining from the same vent between Feb. 25 and March 4, 1983. Episode 3 occurred between March 21 and April 9, with activity at the same vent and at the new O-vent, named for its location on the letter "O" in the word "flow" on the topographic map of the area. This new vent was later renamed Pu‘u ‘O‘o.

Episodes 4-47: Pu‘u ‘O‘o Cone

By episode 4, which began on June 13 and ended on June 17, activity had settled at the Pu‘u ‘O‘o vent. During the next three years, the 255-meter (835-foot) high Pu‘u ‘O‘o cone was constructed by 44 episodes of high-fountaining, most lasting less than a day. ‘A‘a flows from Pu‘u ‘O‘o repeatedly entered the Royal Gardens subdivision in 1983 and in 1984 and destroyed 16 residences. By the time the eruption shifted about 3.2 kilometers (2 miles) downrift in July 1986, it had covered 42 square kilometers (16 square miles of land).

Episode 48: Kupaianaha

The next vent to form, Kupaianaha, was characterized by continuous, quiet effusion of lava. A lava pond formed over the new vent, and its overflows built a broad, low shield. After weeks of eruption, the channel leading from the pond roofed over, forming the beginning of a tube that would reach the ocean, nearly 7.5 miles away, by December 1986. These tube-fed flows destroyed 11 homes in sparsely populated Kapa'ahu; a separate flow to the east destroyed an additional 17 homes in the more densely populated Kalapana Gardens subdivision. Over the next several years, lava continued to enter the ocean through a complex and changing network of tubes, destroying the Hawai‘i Volcanoes National Park Visitor Center at Waha‘ula and an additional 33 homes in Kapa'ahu, lower Royal Gardens, and in the National Park as the flow field widened.

In April 1988, the eruption stopped for one week - the first period of repose since July 1986. A series of 12 brief pauses in the eruptive activity began in February 1990 and continued until November 1990. During the first of these pauses, the tubes feeding lava to the ocean became blocked, and when the eruption resumed, surface flows sent lava once again towards Kalapana. The volume and depth of the active lava in the Kupaianaha pond steadily diminished during early 1990, and by June 1990, the pond was empty. Lava flowed directly from the vent into the tube system wihtout being visible on the surface. by the end of 1990, all of Kalapana was overrun, and 100 additional homes were destroyed by tube-fed lava flows.

Upper East Rift Intrusions

In December 1990, and again in March and August 1991, magma from the summit intruded into the upper East Rift Zone, but with little effect on the ongoing eruption at Kupaianaha. By the middle of 1991, the volume of lava erupted at Kupaianaha began to decrease. As the level of lava in the tube dropped, collapses of the tube walls and roof formed blockages in the lower reaches of the tube system and the lava delivered to the ocean near Waha‘ula diminished in volume, stopping altogether in early September 1991. As the tube system atrophied over the next two months, the terminus of the tube retreated closer and closer to the vent. In October, two additional homes in Royal Gardens were destroyed by some of the last large surface flows to erupt from Kupaianaha.

Episode 49: A New Fissure

On November 8, 1991, the eruption abruptly changed once again, with a curtain of fire erupting from a series of discontinuous fissures between Pu‘u ‘O‘o and Kupaianaha. This event, episode 49, continued until November 26 and fed ‘a‘a flows to the top of Royal Gardens but did not reach any of the remaining houses. Throughout eruptive episode 49 and after its demise, tube-fed pahoehoe flows continued to erupt from nearby Kupaianaha, although their volume was significantly reduced. The episode 49 ‘a‘a flow mainly covered earlier flows from Pu‘u ‘O‘o and from Kupaianaha. The volume of lava erupted from Kupaianaha continued to decline after episode 49 until February 6, 1992, when the last, sluggish flows from Kupaianaha issued from the tube about 2 km (1.25 miles) downslope of the vent.

Episode 50: Pu‘u ‘O‘o Fissure

On February 17, a new 150-meter-long fissure opened on the uprift flank of the Pu‘u ‘O‘o cone and formed a large, perched pond just north of the rift. This eruptive episode, number 50, lasted until March 3, when the eruption abruptly shut down, coincident with an intrusion in the upper East Rift Zone near Pauahi Crater.

Another East Rift Intrusion

The seismic swarm associated with the intrusion on March 3, 1992, consisted of nearly 2,400 recorded earthquakes. At the same time, the summit region began to deflate sharply as magma migrated from beneath the summit into the rift zone. As magma migrated from beneath the summit into the upper East Rift Zone, the area around Pauahi Crater uplifted by about 5 centimeters. A new ground crack about 15 centimeters wide crossed Chain of Craters Road near Devil's Throat Crater. Measurements made after the intrusion showed a total of 30 centimeters of extension in the Devil's Throat and Pauahi Crater area.

Episode 51: Activity Resumed

On March 7, the episode 50 fissure extended slightly higher on the flank of Pu‘u ‘O‘o, forming several new vents. These vents (called the episode 51 vents) have been sporadically active ever since, with more than a dozen eruptive periods lasting from 3 hours to 6 days.

Over the last 10 months, the episode 51 vents have produced a 60-meter high lava shield against the uprift flank of Pu‘u ‘O‘o. From the base of the shield, a broad flow field gradually extended toward the south. The vents soon settled into a pattern of quiescent effusion with only low-level spattering. A lava pond formed atop the shield early in episode 51. Although it resembled the Kupaianaha pond, which was fed by vents directly beneath it, the 51 pond was fed via a tube leading from vents 50 meters to the east of the pond. By mid-July, the lava tube had bypassed the pond, and it has been empty ever since.