Saturday | July 04, 2015
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A new lava flow begins as another ends

For the past year, the Kahauale‘a 2 lava flow was erupting from a vent high on the northeast crater rim of Pu‘u ‘O‘o, on Kilauea’s East Rift Zone, sending lava toward the northeast.

Although this lava flow advanced very slowly, and erratically, it was uphill from residential areas and posed a potential future hazard. Several interruptions to the lava supply at the vent occurred during the past year, but nothing quite large enough to terminate the flow.

In the early morning hours of Friday, June 27, the terminal event finally arrived.

Prior to June 27, HVO was tracking inflation at Pu‘u ‘O‘o for several weeks. Several small lava flows erupted from spatter cones on the Pu‘u ‘O‘o crater floor in the week before the event — another sign of pressurization and high lava levels.

Slow deflation of the cone began by about 5:30 a.m. June 27, about the time a handful of small earthquakes appeared. The deflation and the earthquakes might have represented magma starting, or trying, to intrude through the cone.

The breaking point was finally reached just before 7 a.m.

Our webcams showed a portion of the northeast flank of Pu‘u ‘O‘o pushed up slightly — perhaps several meters (yards) — as magma forced its way through the side of the cone. Magma reached the surface moments later, tearing open new fissures on the northeast flank and sending out a gush of lava as the built-up pressure was released.

Bursts of seismic tremor, sharp deflation, and sagging of Pu‘u ‘O‘o’s crater floor accompanied the opening of the new flank vents as magma stored beneath the cone drained out to feed the new flows.

The initial phases of this new activity were impressive.

Four fissures opened, with the most vigorous being the lowest in elevation. This fissure sent out a beautiful channelized flow on the opening day, reaching about 1.5 km (0.9 miles) in length, but the vigor of the eruption soon abated as the excess pressure in Pu‘u ‘O‘o was relieved.

By the second day, activity focused on the lowest fissure, and flows were extending only a short distance from this vent.

These short flows have been stacking up on one another, building a broad lava shield on the flank of Pu‘u ‘O‘o. This lava shield activity continues today.

The June 27 breakout followed a pattern we observed before.

During 2011, several cycles of pressure buildup in the magmatic system resulted in new vents forming on, or near, Pu‘u ‘O‘o.

In each case, the new vents acted as a kind of pressure release “valve.”

But this has occurred in several ways.

The March 2011 Kamoamoa eruption resulted from a failure in the deeper conduit that is supplying magma from the summit, along the East Rift Zone, to Pu‘u ‘O‘o. Because that magma originated from a depth of several kilometers, it was still rich in gas when it rose to the surface, driving several days of spectacular lava fountaining.

The June 27 event had no such fountaining, likely because the magma was drawn from a shallow depth and was already partly degassed.

In this way, it was roughly similar to the August 2011 breakout, which again resulted from magma beneath Pu‘u ‘O‘o intruding through the side of the cone.

A simple analogy is punching a hole in the side of a bucket filled with water. The flow rate through the hole will be greatest at the start, driven by the hydraulic head pressure of the water column. As the water level drops, this hydraulic pressure drops with it, and the flow rate decreases.

Compared to previous events, the June 27 breakout was relatively small, but it had an important effect on the East Rift Zone eruption.

The lava level drop in Pu‘u ‘O‘o resulted in the lava supply to the Kahauale‘a 2 flow being shut off. This killed the Kahauale‘a 2 flow, but might have simply replaced it with a new long-term hazard concern.

The lava from the June 27 breakout is, like the Kahauale‘a 2 flow, heading in a northeastern direction and could eventually pose a similar threat to downslope communities.

The June 27 flows are, however, very slow-moving and pose no imminent threat. Continued mapping and monitoring of this new flow will help us determine what it could have in store for the future.

Kilauea activity update

A lava lake within Halema‘uma‘u produced nighttime glow visible via HVO’s webcam during the past week. The lava lake level varied slightly but was roughly 35 meters (115 feet) below the rim of the Overlook Crater.

On Kilauea’s East Rift Zone, a new breakout from the northeast flank of Pu‘u ‘O‘o occurred June 27. This created a new flow, directed northeast.

As of July 3, this flow was building a lava shield on the northeast flank of Pu‘u ‘O‘o, and the flows have not extended more than 1.5 kilometers (0.9 miles) from the new vent. This new flow cut off lava supply to the Kahauale‘a 2 flow; the Kahauale‘a 2 flow is no longer active.

One earthquake was reported felt during the past week on the Island of Hawaii.

On Wednesday, July 2, a magnitude 2.6 earthquake occurred 7.5 kilometers (4.7 miles) southeast of Waimea at a depth of 24.6 kilometers (15.3 miles).

Visit the HVO website (http://hvo.wr.usgs.gov) for past Volcano Awareness Month articles and 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.

 

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