Volcano Watch — Kīlauea's Pu`u `O`o eruption: 2005 highlights

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None of these had lasted more than a month. But here we are, 23 years later, and it's still going-the longest rift-zone eruption in recorded history. Yes, Kīlauea once had a persistent lava lake at its summit for a century, but no rift-zone eruption in the last 600 years has rivaled the duration of Pu`u `O`o.

Since the Pu`u `O`o eruption anniversary conveniently coincides with the arrival of the new year, this is a good time to review the previous year's eruption highlights.

Overall, activity at Pu`u `O`o was subdued as 2005 began. Crater vents were incandescent, but were otherwise quiet. The Prince Kuhio Kalanianaole (PKK) lava tube system-which started to form in March 2004-was carrying lava from the southwest flank of Pu`u `O`o toward the ocean. There were numerous lava breakouts from the PKK tube system on Pulama pali and the coastal plain, but there were no active ocean entries.

Action at Pu`u `O`o-both within the crater and on the southwest flank of the cone-began to pick up in late January. Crater vents started producing spatter, and the Martin Luther King (MLK) and Puka Nui vents on the southwest flank began emitting spatter and small lava flows. The increase continued in early February. New spatter cones formed within the crater and at the MLK and Puka Nui vents. Activity peaked on February 9-10, when a dome fountain as much as 8 m (25 feet) high appeared at the MLK vent, feeding large lava flows. Puka Nui also contributed flows. Activity then gradually waned, with the southwest flank vents producing small lava flows until mid-March.

For the remainder of the year, activity in the crater and the southwest flank has been dominated by collapse events. Most of these were rather small. But in October, dramatic step-wise subsidence of the southern crater floor and crater wall produced large pits and cracks. This was accompanied by large-scale subsidence at and near the vents on the southwestern flank of the cone.

The 2005 ocean entry story was complicated, with a bewildering number of entries that waxed, waned, and fizzled out. Some of these lasted less than a day. The entry that was to dominate the story-the East Lae`apuki entry--began in early May. The resulting lava bench grew rapidly, and small collapses began to occur. Because of safety concerns, the National Park Service area was closed to visitors in early July. By early August the area of the bench had reached 11.8 hectares (30 acres). A large collapse occurred on August 27, resulting in the loss of 4.5 hectares (11 acres).

The lost acreage was replaced by mid-October. The bench continued to grow slowly, and as the end of November approached, its area was at least 13.8 hectares (34 acres). On November 28, a series of collapses removed the entire bench as well as 4 hectares (10 acres) of the adjoining older terrain. When the dust settled, the new sea cliff was as much as 50 meters (yards) inland of its predecessor. This constitutes the largest ocean-entry collapse during the Pu`u `O`o eruption. The collapse was accompanied by steam explosions as hot rock and lava mixed with sea water. The explosions propelled rocks and molten spatter as much as 100 meters (yards) inland of the new sea cliff.

The collapse truncated the lava tube that had been feeding the ocean entry. Lava poured from the exposed tube several meters below the top of the new sea cliff. The lava stream arched over into the sea, like water from a fire hose. This spectacle only lasted a few days before the tube crusted over. Yet another lava bench is currently under construction.

The area was closed because of concern for such a collapse, and it remains closed because the growth/collapse cycle is likely to be repeated. Anyone unfortunate enough to be on or near one of these bench collapses risks bombardment by rocks and spatter or, worse yet, a short, unpleasant ride into the sea on a disintegrating mass of lava.

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source near Pu`u `O`o to the ocean, with scattered surface flows breaking out of the tube below the 1900-foot elevation. Flows are visible intermittently on the steep slope of Pulama pali and on the coastal plain. As of December 29, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park.

Access to the ocean entry and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

No earthquakes were felt on Hawai`i Island during the week ending December 28.

Mauna Loa is not erupting. During the week ending December 28, nine earthquakes were recorded beneath the summit area. Six were short-period events at shallow depths (less than 5 km) south of the summit. The other three were deep (greater than 40 km) long-period events. Inflation of Mauna Loa continues.