Volcano Watch — Newest episode likely to stop flowing in weeks

Episode 50 began about 7:30 p.m. on Feb. 17 from a small fissure just southwest of the Pu`u `O`o cone. By the 19th, only about 100 feet of the original fissure was still active. The activity has since settled down at one main point near the northeastern end of the fissure. By Friday, this vent had created a spatter cone almost 25 feet high. 

Inside the cone, a dome-shaped fountain of lava rises about 20-25 feet above the flows. Earlier in the week, the main part of the flow was headed south towards the coast, but by Friday morning, the flows to the south were mainly stagnant whereas a new one was headed north. This flow ponded within about 500 feet of the vent, but the pond was overflowing in several directions, mainly towards the northwest. The flows on Friday were all shelly pahoehoe which were overtopping `a`a flows from the same fissure earlier in the eruption.

The lava pond inside Pu`u `O`o is still about 90-100 feet below its level prior to the beginning of episode 50. The pond is quieter this week; it is alternately crusted over and active. The degassing of magma inside Pu`u `O`o before being erupted at the episode 50 vent explains the low fountain heights at the episode 50 vent. This is similar to what occurred throughout the eruption at Kupaianaha from 1986-1992 and during the episode 49 fissure eruption in November. 

The summit of Kīlauea subsided rapidly as stored magma moved down the rift to the eruption site from the 17th to the 22nd; since then there has been little change in the summit tilt, with periods of slight inflation interspersed between periods of slow deflation. Starting on the 21st and 22nd, the number of intermediate-depth earthquakes increased beneath Kīlauea's summit. This type of earthquake probably indicates upward movement of magma into the summit storage reservoir.

The Kupaianaha vent is now inactive; hardly any fume is emitted from its summit any longer. In the December 29 column, we forecast that the Kupaianaha vent would stop erupting in the next few months; it actually stopped on February 6. A linear fit to the declining eruptive volumes in the tube, measured from April to November 1991, forecast that the tube system would contain no lava on February 5, a projection that is amazingly close to the actual demise of the tube from Kupaianaha. In that same column, we forecast that the nine-year long eruption would not be over when the Kupaianaha vent stopped, but rather that another fissure eruption, similar to the episode 49 fissure, would break out after Kupaianaha stopped. 

Episode 50 is that new eruption; we thought, however, it would most likely occur near the episode 49 fissure (just downrift from Pu`u `O`o), rather than on the uprift side of Pu`u `O`o. We also felt that the new fissure eruption would last only a few weeks, like the episode 49 fissure. Ten days after its onset, the current eruption is of significantly larger volume, probably somewhat more than 1.5 million cubic yards of bubble-free lava per day, than was episode 49. It is possible that the episode 50 vent could evolve into another long-lived one like Kupaianaha, but we suspect that this is unlikely and that episode 50 will stop within a few weeks. 

Even that will not mark the end of the eruption, as other episodic fissure eruptions will probably occur near Pu`u `O`o as long as the pond remains active inside the cone. After the Pu`u `O`o pond is gone, we anticipate that the eruption will migrate farther uprift. In the long term, the nine-year long eruption is winding down, but the next few years will most likely continue to be marked by episodic activity.