Saturday | June 25, 2016
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Puu Oo hits middle age — and it shows

Kilauea’s east rift zone eruption surpassed 30 years of activity in January. But this month marks the 30th anniversary of Puu Oo, which became the dominant eruptive vent in June 1983. When eruptive activity shifted eastward three years later, the Puu Oo cone, built by high lava fountains, stood 835 feet above the surrounding landscape.

In the years since, Puu Oo’s unique prominence has been slowly erased. Its decline started in 1987 with the formation of a crater that began to consume the top of the cone. In 1992, when the eruption shifted back to Puu Oo, nearly continuous eruption from vents on the flanks of Puu Oo began to mantle the cone with lava flows, and the formation of collapse pits on the western side of Puu Oo destroyed even more of the cone.

Today, the once steep-sided pyroclastic cone has been mostly buried beneath a broad “shield” of lava. Only its northern flank has remained unaffected. Repeated collapse of the top of Puu Oo has constructed a 560-by-1,475-foot crater, and the cone has lost a third of its 1986 height.

Following Puu Oo’s most recent large collapse in August 2011, the crater refilled until lava overflowed both its eastern and western sides. Then, in September 2011, the Peace Day fissure opened high on the cone’s eastern flank , but caused only a slight subsidence of Puu Oo’s crater floor.

The Peace Day fissure remains active today and continues to feed active lava flows on the coastal plain west of Kalapana. Following the establishment of the Peace Day vent, Kilauea’s east rift zone eruption entered a months-long period of relative quiescence, with weak surface flows near the coast and almost no activity within Puu Oo.

Eruptive activity picked up again in October 2012, when lava began to erupt from several spatter cones on Puu Oo’s crater floor, filling the crater to its eastern rim.

In January 2013, lava began to regularly overflow onto Puu Oo’s eastern flank. A spatter cone located at the northeastern edge of Puu Oo’s crater fed the Kahaualea flow, which advanced three miles to the northeast before stopping in mid-April. This was the first sustained lava flow fed directly from Puu Oo’s crater since the eruption began 30 years ago.

In early May, a new flow — the Kahaualea II flow — erupted from the northeast spatter cone on Puu Oo’s crater floor. This flow advanced along the edge of the earlier Kahaualea flow and began spreading to the north of Puu Oo. Despite its being active for a month, the Kahaualea II flow is relatively small and has traveled only about 1.2 miles.

The amount of magma erupting at Puu Oo has increased over the past nine months, and not all of it can escape through the Peace Day fissure. The excess lava erupted instead in Puu Oo’s crater, feeding first the Kahaualea flow, and now the Kahaualea II flow.

Unless the Kahaualea II flow is able to capture a greater portion of Puu Oo’s eruptive volume or the output increases substantially, it is unlikely to advance very far.

The more likely scenario is that the Kahaualea II flow will continue to accumulate near the northern base of the cone, which was not previously buried by a lava shield as were the other flanks of Puu Oo.

Perhaps Puu Oo has reached middle age and will continue to erupt for years, or even decades, to come. If so, it may one day be completely buried beneath its own lava and — rather than being the steep-sided cone it once was — become a broad shield that resembles some of the older eruptive centers that adorn Kilauea’s east rift zone, such as Kane Nui O Hamo.

Puu Oo has provided scientists with the first opportunity to observe the early evolution of a long-lived east rift zone eruptive vent. Let us hope it goes “gentle into that good night.”

Kilauea activity update

A lava lake within the Halemaumau Overlook vent produced nighttime glow visible from the Jaggar Museum overlook and via HVO’s webcam during the past week. The lava lake rose slowly during the week, reaching 150 feet below the floor of Halemaumau by Thursday.

On Kilauea’s east rift zone, breakouts from the Peace Day tube remain active at the base of the pali and on the coastal plain.

Small ocean entries are active on both sides of the Hawaii Volcanoes National Park boundary. The Kahaualea II flow, fed from a spatter cone on the northeast edge of Puu Oo crater, continues to spread north of Puu Oo.

Two earthquakes were reported felt across the Hawaiian Islands in the past week. At 2:12 p.m. Tuesday, a magnitude-5.3 earthquake occurred 31 miles south of Kalapana at a depth of 25 miles. At 3:10 p.m. Wednesday, a magnitude-3.6 earthquake occurred 29 miles west-southwest of Kailua-Kona at a depth of 23.8 miles.

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