# Volcano Watch — Volcano rattles at 400 quakes an hour

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An intense earthquake swarm occurred beneath the upper to middle East Rift Zone of Kīlauea Volcano starting at 11:36 p.m. on Sunday, February 7. At the peak of activity, the seismic network operated by the Hawaiian Volcano Observatory was recording nearly 400 earthquakes per hour.

An intense earthquake swarm occurred beneath the upper to middle East Rift Zone of Kīlauea Volcano starting at 11:36 p.m. on Sunday, February 7. At the peak of activity, the seismic network operated by the Hawaiian Volcano Observatory was recording nearly 400 earthquakes per hour. The earthquake swarm settled in the area between Mauna Ulu and Makaopuhi Crater and consisted of about 5,000 separate earthquakes.

From Sunday night to late Tuesday, strong harmonic tremor was recorded beneath the summit as magmadrained out and migrated down the East Rift Zone. The earthquake swarm near Makaopuhi Crater slowly decreased in intensity over the last few days but is still continuing, with about 10 small earthquakes every hour. The strong tremor recorded at the summit slowly decreased in amplitude and was near background levels by Thursday.

At the same time the earthquake swarm began, the summit deflated as magma migrated out from beneath the summit region and into the upper East Rift Zone. The summit deflation ceased about noon Tuesday, and since then, the summit has been slowly reinflating as new magma arrives from below.

The eruption at the episode 51 vents stopped during the night on Sunday and, by 4:30 a.m. Monday morning, the volume of lava entering the ocean had declined markedly. As the volume of the ocean entries decreased, sea water entered the lava tubes at the coast, and the interaction of hot rock and cold sea water resulted in strong steam explosions. The last lava flow entered the sea at about 7:30 a.m. on Monday. The entire floor in the Puu Oo Crater collapsed sometime on Tuesday. No lava was visible in either Puu Oo or in the collapsed pit at the episode 51 vents until Wednesday afternoon, when a small lava pond formed inside Puu Oo.

Following three-and-a-half years of continuous eruptive activity at the Kupaianaha vent, from July 1986 to February 1990, a long sequence of small to large events has interrupted the activity. Between February and November 1990, the Kupaianaha eruption paused 12 times. The period of pauses was followed by a sequence of intrusions similar to the one that occurred this week. The first three of these intrusions occurred during episode 48 (the Kupaianaha vent) on December 4, 1990; March 26, 1991; and August 21, 1991. The next intrusion took place on March 3, 1992, after the November 8-26, 1991, episode 49 fissure eruption between Puu Oo and Kupaianaha and the end of the activity at the Kupaianaha vent on February 6, 1992. The March 3 intrusion occurred between episodes 50 and 51. During that intrusion, the eruption stopped for four days before recommencing from vents slightly higher on the west flank of the Puu Oo cone. Episode 51 has been characterized by 18 pauses, lasting from as briefly as three hours to as long as 6.4 days, with the added interruption of the October 1992 eruption from the episode 52 vents on the south flank of Puu Oo.

It seems most likely that the eruption will recommence near the episode 51 vents, slightly uprift from Puu Oo, within a few days to a week. Because of the large-scale collapse in Puu Oo Crater, the magmatic plumbing has probably been disrupted, and the next episode of the eruption may occur at a new vent, rather than reoccupying the episode 51 vents. In addition, when activity resumes, the flows probably will not be able to reoccupy the same tube system, and surface flows will have to build a new tube to carry the lava to the coast. The flows from the episode 51 vents took more than one month to construct the tube that carried lava to Kamoamoa, and any new tube system will probably take at least as long to construct.

All of the pauses, intrusions, and relocation of the eruptive vents indicate that the eruption continues to wane. This process of slowing down has already been underway for three years and will probably continue for another year or more. We expect the eruption to continue its somewhat erratic behavior, with even more pauses and intrusions, and shifting of the active vent location, as the eruption continues to wind down.