Volcano Watch: West Puu Oo flank vents erupt — once again

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This Quicktime movie shows a timelapse sequence taken from a thermal camera on the south rim of Pu`u `Ō `ō, beginning just before noon on August 3. Just after 2pm, the lava lake and surrounding floor abruptly drop. As the lava lake drops, solidified portions of the crater floor slide into the fluid lava. By the end of the sequence, the floor of the crater is composed of only hot rubble and inclined blocks of the pre-existing crater floor. The temperature scale is degrees Celsius.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

This Aug. 3 photo shows the collapsed floor within Puu Oo Crater in the foreground and two lava flow branches each burning some forest – northwest branch to the right and south branch to the left. (Photo courtesy of Hawaii Volcanoes Observatory)

With volcanoes, we often learn by comparing current events with those of the past. We can even make limited forecasts based on past scenarios if they are sufficiently similar.

The Aug. 3 collapse of the Puu Oo crater floor, accompanied by the eruption of a high-volume lava flow from a vent on the cone’s west flank, is similar to other events on Puu Oo during the past 20 years. For example, this week’s event is akin to the Mother’s Day event May 12, 2002.

In early 2002, lava was intermittently active in several small pits within the Puu Oo crater floor, and tubes fed lava flows down Kilauea’s south flank, destroying one house in the Royal Gardens subdivision, 6 km (4 mi) away.

Throughout the spring, Puu Oo activity slowly increased, resulting in two brief surges of lava within the crater in April. Early in the month, lava ponded in a pit immediately west of Puu Oo Crater.

This pit eventually overflowed, producing a lava flow that advanced 800 m (0.5 mi) to the south-southeast. Then, at the end of April, lava erupting from the east half of the crater floor filled Puu Oo to within 12 m (40 ft) of its east rim.

Subdued activity continued until the morning of May 12, 2002 — Mother’s Day. At 7:40 a.m., a tiltmeter on the north flank of Puu Oo began recording rapid inflation.

About an hour later, high-volume lava flows gushed from two vents 100 m (300 ft) apart on the west flank of Puu Oo cone. Lava first traveled west, then turned to the southwest, and advanced along the edge of previous flows, sparking the largest forest fire from Kilauea’s east rift zone eruption at the time.

The initial lava output was estimated at 8 million cubic meters per day (1,500 gpm), but decreased over the following days. Lava reached the ocean July 19, about five weeks after it first erupted. Interestingly, gas emissions did not increase from this outbreak on Puu Oo’s west flank.

Flash forward to 2011. In early March, Puu Oo collapsed prior to a four-day fissure eruption to the west, and, by the end of the month, lava was refilling the crater.

On July 3, the crater floor began to inflate like a balloon, with the perched lava lake within the crater resembling a recessed pool on top of a large dome. The rapid increase in subsurface pressure beneath the crater floor signaled impending change.

Sure enough, in late July, lava erupting from vents within Puu Oo filled two small pits just west of the crater. Lava spilled out of those pits July 25, feeding a small lava flow toward the southwest. Lava activity and crater floor uplift in Puu Oo diminished July 30 but resumed Aug. 1.

Then, Wednesday, Aug. 3, at about 2 p.m., the domed floor of Puu Oo Crater started to subside. Fifteen minutes later, lava burst from the west flank of the Puu Oo cone, flooding downslope areas and forming a branched flow.

The weaker northwest branch flowed into the forest on the north side of the rift zone, while the much more vigorous south branch quickly moved downslope along the west side of the Mother’s Day flow field, advancing 3.6 km (2.2 mi) in 3 hours. Preliminary lava production estimates are at least twice the rate of the 2002 flow, and gas emissions increased by a factor of 10 to 5,000-7,000 tonnes/day.

Although the lava flow has now diminished, based on similar past events, it might last from days to weeks, or perhaps months. The volume of erupted lava has already equaled, or exceeded, the volume of the Puu Oo crater collapse, so the flow is possibly being fed directly from the rift zone.

As of this writing (Aug. 4), the lava flow is still active — and only time will tell how long it will last. HVO webcams (http://volcanoes.usgs.gov/hvo/cams/) are providing excellent coverage of the events.

We continue to monitor the activity closely, and will post daily eruption updates on the HVO Web site (http://volcanoes.usgs.gov/hvo/activity/kilaueastatus.php).

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