Volcano Watch — Kīlauea has busy week; new episode begins

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The nine-year long eruption along the East Rift Zone of Kīlauea Volcano took two dramatic turns this past week, but ended up nearly where it started. 

The changes began about 1:00 a.m. Tuesday, when a swarm of small earthquakes began beneath the upper East Rift Zone in the vicinity of Pauahi Crater. The swarm consisted of nearly 2,400 separate events recorded on the U.S. Geological Survey's seismic network; roughly a half dozen were large enough to be felt by residents in Volcano. 

At the same time, the summit region began to deflate sharply as magma migrated from beneath the summit into the rift zone. Campers reported that the episode 50 vent stopped erupting between 1:30 and 2:00 a.m. and by 9 a.m. the lava pond inside Pu`u `O`o cone had also drained out of sight. The `a`a flows from the episode 50 eruption continued to advance until about 4:00 p.m., apparently fed from lava stored in a perched pond just north of the episode 50 vent. 

As magma migrated down the upper East Rift Zone, the area around Pauahi Crater bulged upwards by perhaps a foot, as seen in changes recorded at our electronic tilt instrument at Pu`u Huluhulu. A new ground crack about 5-6 inches wide crossed Chain of Craters Road near Devil's Throat, several hundred feet below the intersection of Hilina Pali and Chain of Craters Roads. This crack continued to widen overnight, and by 9:00 a.m. Wednesday morning it was about one-half inch wider than it was the previous evening. The total extension along the Chain of Craters Road was about 12 inches, of which half was in the crack near Devil's Throat and half was apparently in a zone of small cracks near Pauahi Crater.

By 9:00 a.m. Tuesday, the deflation of the summit had slowed and the number of earthquakes in the Pauahi Crater area had declined to about 30-60 per hour from the peak of nearly 500 per hour recorded between 1:00 and 2:00 a.m. By 8:00 a.m. the deflation of the summit had flattened out, and by 9:00 a.m. the summit began to reinflate with magma coming up from deeper in the volcanic system. The intrusion of magma into the upper East Rift Zone had therefore stopped by about 8:00 a.m. and no new eruption resulted. In the past few years, there have been several other intrusions of magma into the upper East Rift Zone that did not result in new outbreaks of lava. 

The most surprising thing about the intrusion was that it stopped the eruption at the episode 50 vent and drained the pond inside Pu`u `O`o, rather than adding magma supply to the episode 50 eruption. The episode 50 vent remains inactive, but lava returned inside Pu`u `O`o late Tuesday. However, this lava is deep inside the crater and we see no signs that it is refilling the crater. The absence of magma movement downrift from Pauahi Crater area to resupply Pu`u `O`o indicates a blockage in the rift zone near Pauahi Crater. 

At 4:03 a.m. Wednesday morning, a magnitude 3.2 earthquake occurred near Devil's Throat. This earthquake may have been the cause of the continued extension across the cracks in the road on Wednesday. The summit continued to rapidly reinflate with magma until about 5:00 a.m. yesterday when the summit began to deflate slowly.

At about 1:30 p.m. yesterday, lava once again began erupting from near the episode 50 vent on the west side of Pu`u `O`o. The new fissure is slightly higher on the Pu`u `O`o vent than the episode 50 vent. The flows are apparently heading toward the north, as they did during most of episode 50. The pond in Pu`u `O`o is back to the level it was during the episode 50 eruption; it apparently refilled starting yesterday morning, when the summit began to deflate. The magma intruded this past Tuesday into the upper East Rift Zone near Pauahi Crater has not migrated down the rift zone; the new eruption is being fed directly from the summit and bypassing the underground pool of magma intruded last Tuesday. The new eruption is the 51st episode in the nine-year-long eruption of Kīlauea Volcano.

Episode 51, like episodes 49 and 50, will probably not be long-lived. We expect the new vent to stop within a few weeks. Activity probably will continue to be episodic and will eventually migrate uprift toward the summit. The long-term prognosis is still that the nine-year eruption is waning, as seen in significantly lower emission of sulfur dioxide gas from the summit than was measured a few years ago.