Volcano Watch — A volcano that just keeps rolling along: Hawaiian Volcano Observatory tracks eruption's phases

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. Today, January 3, marks the tenth anniversary of the beginning of the eruption. During those 10 years, roughly 1.6 cubic kilometers of lava have been erupted; each day another 100,000 cubic meters is added to that total. The flows have covered Chain of Craters Road from east of Kalapana to just west of Kamoamoa and have destroyed 184 houses. The eruption has had a number of distinct periods characterized by activity at different vents and by different eruptive styles. The map shows the areas covered by flows during these different periods of activity. The following is a summary of the activity, starting from the initial outbreak.

Episodes 1-3: The Initial Fissure Eruption

The eruption began early on January 3, 1983, when a discontinuous five-mile long series of fissures opened in, and downrift of Napau Crater. This fissure opened progressively farther downrift over a period of four days. The fissure ended near the prehistoric cone of Kalalua at the downrift end. Activity 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 in vigorous fountaining from the same vent between February 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: Construction of the 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, located slightly uprift from the 1123 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: The Kupaianaha Shield

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. The photograph shows this shield surmounted by the active lava pond; the large cone in the background is the Pu`u `O`o cone. After weeks of eruption, the channel leading from the pond roofed over, forming the beginning of a tube that would reach the ocean, nearly 12 kilometers (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 without 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. 

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: Fissure on the Flank of Pu`u `O`o

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 Upper East Rift Zone 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 intruded 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: Fissure 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 8.5 hours to 20 days, broken by repose 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. 

Changes at Pu`u `O`o 

Since the eruption shifted to Kupaianaha in 1986, the Pu`u `O`o conduit has enlarged from 20 meters to a gaping crater 300 meters across. At the same time, the Pu`u `O`o cone has been reduced in height by about 20 meters, due to collapse of the unstable structure. A lava pond has been active at the bottom of the crater throughout much of the last several years, but no lava flows have originated from Pu`u `O`o since 1986. The active pond occupies about a third of the crater floor and varies in height from about 35 to more than 75 meters below the lowest point on the crater rim. 

A new eruptive fissure opened on the night of October 2, 1992, in response to a magnitude 4.3 earthquakelocated 7 kilometers beneath Kīlauea's south flank between the eruption site and the ocean. The two main vents on the fissure fed a vigorous pahoehoe flow that turned to channeled `a`a as it advanced to the south. The episode 51 vents were in repose at the time of the earthquake, but on the following day, they resumed erupting. Both the 51 and 52 vents were active for the next three days, and then the 52 vent began to wane. By mid-October, the 52 vents were dead, while 51 continued to erupt. 

The earthquake that initiated episode 52 apparently altered the plumbing to the episode 51 vents. Following the earthquake, there has been only a single pause in the eruption, lasting less than 24 hours. As a result, the lava tube leading to the south edge of the 51 shield extended in October to the top of the steep slope above the coast, and surface flows advanced rapidly downslope. By November 8, lava had crossed the Chain of Craters Road and entered the ocean at Kamoamoa. In December, virtually all of the lava erupted at the 51 vents was fed directly to the ocean via lava tubes. At the coast, flows buried the Kamoamoa campground, picnic area, and the new black sand beach formed earlier in this eruption by Kupaianaha flows entering the ocean farther to the east. A new lava delta extended 300 meters out to sea and formed 60 acres of new land. On the evening of November 24, spectacular steam explosions formed a 7-to 8- meter-tall littoral cone where lava entered the sea. This cone has since been partially buried by subsequent flows. The lava delta has begun to break apart with the formation of cracks parallel to the coastline. On December 26, a piece of the lava delta slid into the ocean. 

Summary

Since the Pu`u `O`o-Kupaianaha eruption began, about 1,600 million cubic meters (1.6 cubic kilometers) of lava has been erupted. In comparison, Mauna Ulu, the previous longest-lived historic eruption on the East Rift Zone, erupted about 350 million cubic meters of lava between 1969 and 1974.

The eruption has destroyed 181 homes and a number of other buildings, with total losses of about $61 million. As long as the eruption is confined to the episode 51 vents, it poses no immediate threat to residential areas, but it continues to imperil archaeological sites and native plants in Hawai`i Volcanoes National Park. 

The relatively low extrusion rates today compared with those measured a few years ago suggest that the eruption is winding down. This winding-down process probably began at the time of the upper rift intrusions in December 1990, but became more obvious with the demise of the Kupaianaha vent this past February. The trends over the past two years have been towards progressively smaller eruptive volumes and migration of the active vents towards the summit. If these trends continue, the lava pond inside Pu`u `O`o should become inactive, followed by the episode 51 vents. At the same time or shortly thereafter, activity may migrate uprift towards the summit, or the eruption could be over at that point. It has become clear that predicting when, and even where, eruptions will start is easier than predicting when they will end.

The geologic history of the lower and middle East Rift Zone recorded by prehistoric lava flows suggests that more eruptions are highly likely to occur in this area, even after this eruption is finally over. There is no reason to expect that this eruption will mark the end of activity on Kīlauea's middle to lower East Rift Zone, where eruptions have occurred in 1955, 1960, 1961, 1963, 1965, 1968, 1977, and 1983-1993. This sequence of eruptions follows 115 years of no eruptions occurring along this middle-to-lower section of the rift. Future eruptions pose even greater risks to private property, as the area has developed rapidly since the last eruption on the lower East Rift Zone in 1961.