Volcano Watch — Pu‘u ‘Ō‘ō hits middle age—and it shows

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Kīlauea's East Rift Zone eruption surpassed 30 years of activity in January 2013. But this month marks the 30th anniversary of Pu‘u ‘Ō‘ō, which became the dominant eruptive vent in June 1983. When eruptive activity shifted eastward three years later, the Pu‘u ‘Ō‘ō cone, built by high lava fountains, stood 255 m (835 ft) above the surrounding landscape.

Pu‘u ‘Ō‘ō hits middle age—and it shows...

Pu‘u ‘Ō‘ō was still close to its maximum height of 255 m (835 ft) in 1992 (top), although its western flank had been partly buried by a lava shield. Since then, the cone has lost a third of its former height due to collapses, and lava has continued to bury its flanks (bottom). USGS photos.

(Public domain.)

In the years since, Pu‘u ‘Ō‘ō'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. Then, in 1992, when the eruption shifted back to Pu‘u ‘Ō‘ō, nearly continuous eruption from vents on the flanks of Pu‘u ‘Ō‘ō began to mantle the cone with lava flows, and the formation of collapse pits on the western side of Pu‘u ‘Ō‘ō 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 Pu‘u ‘Ō‘ō has constructed a 300- by 450-m (560- by 1,475-ft) crater, and the cone has lost a third of its 1986 height.

Following Pu‘u ‘Ō‘ō'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 Pu‘u ‘Ō‘ō'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, Kīlauea'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 Pu‘u ‘Ō‘ō.

Eruptive activity picked up again in October 2012, when lava began to erupt from several spatter cones on Pu‘u ‘Ō‘ō's crater floor, filling the crater to its eastern rim.

In January 2013, lava began to regularly overflow onto Pu‘u ‘Ō‘ō's eastern flank. A spatter cone located at the northeastern edge of Pu‘u ‘Ō‘ō's crater fed the Kahauale‘a flow, which advanced 5 km (3 miles) to the northeast before stopping in mid-April. This was the first sustained lava flow fed directly from Pu‘u ‘Ō‘ō's crater since the eruption began 30 years ago.

In early May 2013, a new flow—the Kahauale‘a II flow—erupted from the northeast spatter cone on Pu‘u ‘Ō‘ō's crater floor. This flow advanced along the edge of the earlier Kahauale‘a flow and began spreading to the north of Pu‘u ‘Ō‘ō. Despite its being active for a month, the Kahauale‘a II flow is relatively small and has traveled only about 2 km (1.2 miles).

The amount of magma erupting at Pu‘u ‘Ō‘ō has increased over the past 9 months, and not all of it can escape through the Peace Day fissure. The excess lava erupted instead in Pu‘u ‘Ō‘ō's crater, feeding first the Kahauale‘a flow, and now the Kahauale‘a II flow.

Unless the Kahauale‘a II flow is able to capture a greater portion of Pu‘u ‘Ō‘ō's eruptive volume or the output increases substantially, it is unlikely to advance very far. The more likely scenario is that the Kahauale‘a 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 Pu‘u ‘Ō‘ō.

Perhaps Pu‘u ‘Ō‘ō 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 Kīlauea's East Rift Zone, such as Kāne Nui O Hamo.

Pu‘u ‘Ō‘ō 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."

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Volcano Activity Update

A lava lake within the Halema‘uma‘u Overlook vent produced nighttime glow that was visible from the Jaggar Museum overlook and via HVO's Webcam during the past week. The lava lake rose slowly during the week and was 45–46 m (150 ft) below the floor of Halema‘uma‘u as of Thursday, June 6.

On Kīlauea'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 Hawai‘i Volcanoes National Park boundary. The Kahauale‘a II flow, fed from a spatter cone on the northeast edge of Pu‘u ‘Ō‘ō crater, continues to spread north of Pu‘u ‘Ō‘ō.

Two earthquakes were reported felt across the Hawaiian islands in the past week. On Tuesday, June 4, 2013, at 2:12 p.m., HST, a M5.3 earthquake occurred 50 km (31 mi) south of Kalapana at a depth of 40 km (25 mi). On Wednesday, June 5, at 3:10 p.m., HST, a M3.6 earthquake occurred 46 km (29 mi) west-southwest of Kailua-Kona at a depth of 38.3 km (23.8 mi).