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Volcano Watch — Pu‘u ‘Ō‘ō shifts direction again

September 22, 2011

Anyone watching the Webcams positioned on and around Pu‘u ‘Ō‘ō in the early morning hours of Wednesday, September 21, would have seen a marked change in the eruption. Prior to that, a lava lake in the western part of Pu‘u ‘Ō‘ō crater was overflowing, sending lava down the west flank of Pu‘u ‘Ō‘ō cone.

Lava cascades down the east flank of Pu‘u ‘Ō‘ō cone from a fissure that opened on the upper east flank early Wednesday morning.

At about 2:22 a.m. on Wednesday, activity in the crater and in overflows to the west suddenly decreased as a fissure opened on the upper east flank of the Pu‘u ‘Ō‘ō crater. This new fissure fed a channelized pāhoehoe flow that advanced rapidly downslope toward the east. By mid-afternoon on Thursday, the flow, which had transitioned to ‘a‘ā, had advanced 3.7 km (2.3 mi) from the fissure, and was still moving.

A tiltmeter and a GPS instrument on the north flank of the cone started moving away from the fissure area more than a half hour before lava broke the surface, tracking the motion of magma toward the surface.

This fissure opening is very similar to the start of activity in July 2007, when a fissure opened in the same general area. In 2007, the activity localized about 2 km (1.2 mi) east of Pu‘u ‘Ō‘ō cone and fed lava flows for the next 3.5 years.

Those of you who follow Kīlauea's volcanic activity will have noticed that, while the previous four years (since the July 2007 eruption) had been fairly steady-state, this year, we've already seen three shifts in eruptive activity: the Kamoamoa fissure eruption west of Pu‘u ‘Ō‘ō in March, the flows from the western base of Pu‘u ‘Ō‘ō cone in August, and, this week, the fissure high on the east flank of the cone.

All these changes are in response to increased pressure within Kīlauea's magma plumbing system. Prior to the 2007 eruption, pressure was very high because of an increase in magma supply rate from depth, inflating the entire volcano's shallow plumbing system. The high pressure was manifested by uplift and spreading of the summit and rift zone areas and a high stand of lava in the Pu‘u ‘Ō‘ō crater. The 2007 vents to the west of Pu‘u ‘Ō‘ō relieved much of that pressure by initially feeding voluminous lava flows. The summit and rift zones quickly subsided, then subsided more slowly as the flow rates waned.

In 2010, the pattern of subsidence and contraction at the summit turned once again to uplift and extension, and the lava level in Pu‘u ‘Ō‘ō began to rise. It is not clear what caused this inflation—it lacked the characteristic increase in volcanic carbon dioxide emissions that indicate a larger supply of magma from depth. It's possible that the inflation was due to less volume being erupted; possibly the extremely frequent deflation-inflation (DI) cycles were enough of a disruption to restrict flow of lava from Pu‘u ‘Ō‘ō.

The first release of the pressure building since early 2010 was the Kamoamoa fissure eruption, just west of Pu‘u ‘Ō‘ō, in March 2011. That eruption drained Pu‘u ‘Ō‘ō, and it took more than two weeks for lava to return. By July, the lava level was close to the rim once more. In August, the pressure was relieved for a short while by lava from the crater breaking through the cone near its base. Those seeping lava flows lasted only a couple of weeks, and the level of lava in the crater rose once more.

We don't know how long this week's fissure eruption will last, but it is certain that the ever-changing activity at Pu‘u ‘Ō‘ō will keep us and all you volcano watchers intrigued and awaiting the next new phase.


Volcano Activity Update

A lava lake has been present within the Halema‘uma‘u Overlook vent over the past week, resulting in night-time glow visible from the Jaggar Museum. The lake, which is deep within the vent cavity and visible by Webcam, fluctuated in level several times over the past week in response to two deflation-inflation cycles at the summit.

Early this past week, lava within the Pu‘u ‘Ō‘ō crater, on Kīlauea's east rift zone, rose to the crater rim, feeding several relatively short overflows to the west. At 2:20 a.m., HST, on Wednesday, September 21, a new fissure opened on the upper east flank of Pu‘u ‘Ō‘ō cone, sending a vigorous flow outside the crater to the southeast, and causing the lava level in the crater to drop. By the afternoon of Thursday, September 22, this flow was still actively advancing and had traveled 3.7 km (2.3 miles) southeast of Pu‘u ‘Ō‘ō. If this flow continues, it will threaten the Royal Gardens subdivision in the coming days.

Two earthquakes beneath Hawai‘i Island were reported felt this past week. A magnitude-2.0 earthquake occurred at 9:04 p.m., HST, on Sunday, September 18, 2011, and was located 5 km (3 mi) southwest of ‘O‘ōkala at a depth of 15 km (9 mi). A magnitude-1.8 earthquake occurred at 7:19 p.m., on Monday, September 19, and was located 6 km (4 mi) south of Volcano Village at a depth of 4 km (2 mi).

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