Volcano Watch — Eruption resumes after taking a short vacation

The nearly 12-year-long eruption on Kīlauea's east rift zone took a short vacation this past week. No lavaerupted between Wednesday morning and Thursday afternoon, when lava once again reoccupied the same tube to the western ocean entry at Laeapuki and a small channelized 'a'a flow broke out of the tube in the center of the flow field above Kamoamoa. The eastern flow that entered the ocean last Saturday was also active, although the volume was still small. The new breakout started from roughly the same area along the tube at about the 900-foot elevation, where surface flows have issued since mid-August. The start-up of the eruption was gradual, and by noon on Friday, the total volume was still small.

During the evening of October 1, the surface flows along the eastern side of the flow field finally reached the ocean between Kamoamoa and Waha'ula.This new entry, and the old entry point at Laeapuki on the west edge of the flow field, were then both active until the break in activity that began Wednesday. For much of the last month-and-a-half, about 2/3 of the erupted volume has fed the surface flows along the eastern side of the flow field, and the remaining third of the volume has entered the ocean at Laeapuki.

For the last several weeks, the new eastern flows covered vegetated older flows along the eastern margin of the flow field. Methane explosions were numerous as the flows advanced towards the ocean (burning vegatation produces methane, which explodes violently as the flows ignite it). For a short time, burning blacktop from the isolated section of Chain of Craters Road between Kamoamoa and Wahaula added its black plume to the white, hydrochloric acid-rich plumes produced where the lava entered the ocean.

There was also a lava ledge collapse on October 1, when a piece of the newly formed lava bench near the Laeapuki entry slid into the ocean. Such collapses occur without warning and pose a serious hazard along the coast. Not only do sections of what appears to be solid land slide into the ocean, but steam explosions commonly accompany these collapses. Such explosions can hurl blocks of incandescent lava up to several hundred meters inland. In addition, the collapse of the ledge commonly produces a small, local tsunami (biggerthan last Tuesday's!) that can wash boiling seawater over the outer part of the lava ledge.

The pause in activity that began Wednesday was the first in the eruption since April and only the forth since last February. Activity has been nearly steady-state since February 1993, following a year long period with numerous pauses and changes in eruptive vents. Activity for the last two years has been reminiscent of the activity from the Kupaianaha vent from July 1986 to February 1992.

The lava pond inside Pu'u 'O'o, which had been at a constant depth of about 260 feet below the rim of the cone for several months, began to drop in the last few weeks. On Thursday, during the period of inactivity, the pond level was at about 290 feet below the rim. On Friday morning, after the eruption had resumed, the pond level remained deep. In the past, the depth of the pond correlated with periods of activity and inactivity, with pauses corresponding to deep pond levels. The pond level would rise during the pause and the eruption would then resume. This time, the pause began as the pond level decreased, but the pause ended while the pond was still at a deeper level.

The amplitude of harmonic tremor measured near Pu'u 'O'o decreased sharply during the pause but increased again by Thursday afternoon. We also measured an inflation of the summit of Kīlauea Volcano as magmacontinued to be supplied from below, but was stored beneath the summit instead of erupting. On Friday morning, the summit continued to inflate, confirming that the eruption had restarted slowly and that less lava was erupting than was being supplied from below. In the past, we have observed similar gradual increases in eruptive volume. If this follows the pattern of those pauses, then it may take several days before the eruptive volume returns to the high levels we were measuring before the pause.