March 5 marked the third anniversary of the onset of Kilauea’s four-day-long Kamoamoa fissure eruption. This brief episode marked the end of the eruptive vent established east of Pu‘u ‘O‘o in 2007 and presaged a return of activity to Pu‘u ‘O‘o that continues today.
Months before the Kamoamoa eruption began, lava output from Kilauea’s long-lived East Rift Zone eruption, ongoing since 1983, started to wane.
This was coupled with uplift and increased seismic activity at the volcano’s summit and at Pu‘u ‘O‘o. Moreover, the lava lake within Halema‘uma‘u Crater, active at the summit since 2008, started to slowly rise.
Lava flows also began to erupt within Pu‘u ‘O‘o’s crater. The sudden onset of seismic tremor and elevated earthquake activity along Kilauea’s East Rift Zone at 1:42 p.m. March 5, 2011, signaled the start of a magmatic intrusion uprift from Pu‘u ‘O‘o.
Rapid deflation started at Pu‘u ‘O‘o at almost the same time and at Kilauea’s summit about 30 minutes later.
Shortly afterward, most of the Pu‘u ‘O‘o crater floor began to subside, dropping 113 meters (371 feet) in about four hours. Almost simultaneously, the lava lake at Kilauea’s summit began to drain, falling about 143 m (469 feet) before stabilizing. The Kamoamoa eruption began at 5:09 p.m., when lava reached the surface about 2 km (1.2 miles) southwest of Pu‘u ‘O‘o, forming a 1-km-long (0.6-mile-long) eruptive fissure.
A second fissure of the same length opened early March 6 farther to the southwest. These two fissures, designated as “eastern” and “western” fissures, were separated by 360 m (0.2 miles) of heavily cracked ground.
The eruption was initially sporadic, and activity migrated from one spot to another along both fissures and repeatedly started and stopped.
On March 8, however, the eruption became focused near the western end of the western fissure and began to feed a fast-moving channelized ‘a‘a flow that bowled over ‘ohi‘a trees like matchsticks as it advanced downslope.
This activity continued unabated overnight, but late in the afternoon March 9, the western fissure began to wane and finally shut down at about 10:30 p.m. that night, marking the end of the Kamoamoa eruption.
The channelized ‘a‘a flow stalled soon afterward, having reached a total length of 3.3 km (2.1 miles). Altogether, approximately 2.7 million cubic meters (3.5 million cubic yards) of lava erupted, and eruptive sulfur dioxide emissions averaged 8,500 tonnes/day — several times higher than Kilauea’s normal East Rift Zone output at that time.
The summit of Kilauea dropped about 15 cm (6 inches) during the course of the eruption, and the East Rift Zone at the eruption site spread apart by about 3 m (10 feet).
The Kamoamoa eruption was probably a result of the gradual shutdown of the previous East Rift Zone vent — the episode 58 vent — with no slowdown in the amount of lava entering the rift zone.
This led to the pressurization of Kilauea’s magma system, which was manifested as inflation at the summit and at Pu‘u ‘O‘o, spreading of the East Rift Zone, increased seismic activity along the upper East Rift Zone and rising lava levels within the summit vent and Pu‘u ‘O‘o’s crater.
The pressurization culminated in the Kamoamoa fissure eruption, which diverted magma from beneath Pu‘u ‘O‘o and Kilauea’s summit, thereby causing Pu‘u ‘O‘o’s crater floor to collapse and the summit lava lake to drain, respectively. Once the excess pressure dissipated, the pressure gradient between the summit and the East Rift Zone fissure was insufficient to sustain the eruption, and the Kamoamoa eruption stopped.
Afterwards, the pressure climbed within Kilauea’s magma storage areas and transport pathways as the supply of magma to the volcano continued unchanged.
This renewed pressure led to the reappearance of the summit lava lake and eventually restarted eruptive activity at Pu‘u ‘O‘o, which remained the easiest pathway for magma to reach the surface.
Because of the excellent geological, geophysical and geochemical monitoring of Kilauea, progressions in eruptive activity, such as those observed prior to the Kamoamoa eruption, can likely be recognized months in advance of any shifts in eruption style and/or location.
At the moment, no such precursory activity is apparent.
Kilauea activity update
A lava lake within Halema‘uma‘u produced nighttime glow visible via HVO’s webcam during the past week. The lava level fluctuated with a deflation-inflation cycle and varied between 39 and 50 m (130 and 160 feet) below the rim of the Overlook crater.
On Kilauea’s East Rift Zone, the Kahauale‘a 2 flow continued to be active northeast of Pu‘u ‘O‘o. After the flow front stalled in late January at a distance of 7.8 km (4.8 miles) northeast of Pu‘u ‘O‘o, surface flows have been active behind the stalled flow front.
This week, the flows reached the stalled flow front, and are active about 7.8 km (4.8 miles) northeast of Pu‘u ‘O‘o.
Webcam images indicate small forest fires are continuing.
There were no earthquakes reported felt on the Island of Hawaii in the past week.
Visit the HVO website (http://hvo.wr.usgs.gov) for current Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.
Volcano Watch (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.