Revisiting Kilauea

Mauna Loa’s recent indigestion has attracted a lot of attention, stealing the limelight from Kilauea, which has been in nearly continuous eruption for almost 22 years. Let’s see what Kilauea has been up to for the past year or so.

Last fall, active lava flows from the Mother’s Day tube system, which began in May 2002, were in full retreat back toward the source at Pu`u `O`o. The last lava had entered the ocean in July. Thereafter, the terminus of the tube system that delivered lava to the coast began to slowly atrophy. By the end of October, no active flows were on the coastal plain, and, by the end of November, none was below the top of Pulama pali.

The retreat of active lava flows from the coast was accompanied by rejuvenated activity at Pu`u `O`o. Some small lava flows began to appear in Pu`u `O`o’s crater in August. More were emplaced in October and November. The pace then picked up substantially, and, by the end of December, the floor of the crater had been repaved with new lava. In mid-January, a little lava flowed out of the crater through low points on the east and west sides of the crater rim.

Flows also began to appear just outside the crater in October, on the west and southwest flanks of Pu`u `O`o. Flows from these flank vents continued through early January.

Rootless shields and hornitos began to form over the upper part of the Mother’s Day lava tube in late summer 2003. Shield and hornito formation advanced southward during November and December.

Meanwhile, as activity shifted closer to Pu`u `O`o, Kilauea was inflating. The distance between benchmarks on opposite sides of Kilauea’s caldera had changed little since the start of the Mother’s Day tube in May 2002 but had begun to slowly lengthen in March 2003. The rate of lengthening, which indicates inflation of the summit, increased around August.

Very similar symptoms were observed just before the Mother’s Day breakout in 2002. So volcanologists at HVO considered it likely that a breakout from the flank of Pu`u `O`o would form a new tube system.

Well, a new breakout did indeed occur—on January 18, 2004. A new vent, named MLK, opened on the south flank of Pu`u `O`o and, simultaneously, activity within the crater stopped. Lava began to advance toward the southeast. Judging from past experience, volcanologists expected the flows to build a new tube system that would become dominant as the Mother’s Day system gradually died.

But activity at the MLK vent ceased only 5 days later, during a deflation event at Kilauea’s summit. Vents within and just outside Pu`u `O`o’s crater, and vents on the south flank of Pu`u `O`o, were intermittently active through early March. Meanwhile, the Mother’s Day tube system stayed in business.

In mid-March, the persistent activity from the Mother’s Day tube was joined by persistent activity from the south flank vents, which generated a new lava tube. This new tube was named the PKK tube, in honor of Prince Kuhio. Activity within and just outside Pu`u `O`o’s crater stopped.

The older system was clearly getting the lion’s share of magma. In early April, a flow from the southern end of the Mother’s Day rootless shield field began to advance as the rootless shields fell silent. It was named the Banana flow because it originated near a kipuka that contained a few feral banana trees. The Banana flow reached the northern margin of the coastal plain on May 3 and entered the ocean about May 31. The ocean entry from the Banana flow continued until the first week in August. Since then, Banana flow activity has retreated back above Pulama pali. The Mother’s Day tube system is still alive, but its pulse is weak.

During the Banana flow’s advance to the sea and its subsequent retreat, flows from the PKK tube waxed and waned but only briefly made it over Pulama pali in early August.

Right now, the rate of lava production from Pu`u `O`o is low, and Kilauea’s summit is inflating. This indicates that the rate at which lava is erupting from the Pu`u `O`o tube systems is less than the rate at which magma is being supplied to Kilauea from depth. Eventually the eruption rate will have to increase, probably with the formation of a new flank vent at Pu`u `O`o.

Activity Update

Eruptive activity at Pu`u `O`o continues weakly. Lava is not visible in the Banana flow, which breaks out of the Mother’s Day tube above Pulama pali. Scattered breakouts are active within a wide expanse of the PKK flow east of the Banana flow, and one at the top of Pulama pali became visible from the end of Chain of Craters Road on Wednesday night. The eruptive activity in Pu`u `O`o’s crater is weak, with sporadic minor spattering.

One earthquake was reported felt on the island during the week ending September 22. Residents of Hilo felt a magnitude 3.0 earthquake at 9:44 p.m. on September 15. The earthquake was located 3 km (2 miles) northeast of Opihikao at a depth of 10 km (6 miles).

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity was notably high for the 9th week in a row. HVO located 68 earthquakes in the south caldera area, down from 154 the week before. Nearly all of the earthquakes of this ongoing activity are of long-period type, have magnitudes less than 3, and are deep, 40 km (23 miles) or more.

This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by with permission.

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