Volcano Watch — A recap of the Kamoamoa fissure eruption on its third anniversary

Months before the Kamoamoa eruption began, lava output from Kīlauea's long-lived East Rift Zone eruption, ongoing since 1983, had started to wane. This was coupled with uplift and increased seismicity at the volcano's summit and at Pu‘u ‘Ō‘ō. 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 ‘Ō‘ō's crater.

The sudden onset of seismic tremor and elevated earthquake activity along Kīlauea's East Rift Zone at 1:42 p.m., HST, on March 5, 2011, signaled the start of a magmatic intrusion uprift from Pu‘u ‘Ō‘ō. Rapid deflation started at Pu‘u ‘Ō‘ō at almost the same time and at Kīlauea's summit about 30 minutes later. Shortly afterward, most of the Pu‘u ‘Ō‘ō crater floor began to subside, dropping 113 m (371 ft) in about 4 hours. Almost simultaneously, the lava lake at Kīlauea's summit began to drain, falling about 143 m (469 ft) before stabilizing.

The Kamoamoa eruption began at 5:09 p.m., when lava reached the surface about 2 km (1.2 mi) southwest of Pu‘u ‘Ō‘ō, forming a 1-km-long (0.6-mi-long) eruptive fissure. A second 1-km-long (0.6-mi-long) fissure opened early on March 6 farther to the southwest. These two fissures, designated as "eastern" and "western" fissures, were separated by 360 m (0.2 mi) 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‘ā flow that bowled over ‘ōhi‘a trees like matchsticks as it advanced downslope.

This activity continued unabated overnight, but late in the afternoon on 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‘ā flow stalled soon afterward, having reached a total length of 3.3 km (2.1 mi).

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 Kīlauea's normal East Rift Zone output at that time. The summit of Kīlauea dropped about 15 cm (6 in) over the course of the eruption, and the East Rift Zone at the eruption site spread apart by about 3 m (10 ft).

The Kamoamoa eruption was probably a result of the gradual shutdown of the previous East Rift Zone vent—the episode 58 vent—with no slow-down in the amount of lava entering the rift zone. This led to the pressurization of Kīlauea's magma system, which was manifested as inflation at the summit and at Pu‘u ‘Ō‘ō, spreading of the East Rift Zone, increased seismicity along the upper East Rift Zone, and rising lava levels within both the summit vent and Pu‘u ‘Ō‘ō's crater.

The pressurization culminated in the Kamoamoa fissure eruption, which diverted magma from beneath Pu‘u ‘Ō‘ō and Kīlauea's summit, thereby causing Pu‘u ‘Ō‘ō's crater floor to collapse and the summit lava lake to drain, respectively. Once the excess pressure had 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 Kīlauea'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 ‘Ō‘ō, which remained the easiest pathway for magma to reach the surface.

Because of the excellent geological, geophysical, and geochemical monitoring of Kīlauea, progressions in eruptive activity, like 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.

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Volcano Activity Update

A lava lake within Halema‘uma‘u produced nighttime glow that was 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 ft) below the rim of the Overlook crater.

On Kīlauea's East Rift Zone, the Kahauale‘a 2 flow continued to be active northeast of Pu‘u ‘Ō‘ō. After the flow front stalled in late January at a distance of 7.8 km (4.8 mi) northeast of Pu‘u ‘Ō‘ō, 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 mi) northeast of Pu‘u ‘Ō‘ō. Webcam images indicate that small forest fires are continuing.

There were no earthquakes reported felt on the Island of Hawai‘i in the past week.