Volcano Watch — Kīlauea lava flow pauses briefly, then resumes

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The nearly twelve-year-long eruption on Kīlauea's east rift zone had at least one additional pause in activity this past week.

The nearly twelve-year-long eruption on Kīlauea's east rift zone had at least one additional pause in activity this past week.

The lava entry at Lae'apuki, on the west side of the flow field, shut down Monday morning. Monday evening, flows were active along the eastern side of the flow field above Kamoamoa, but no lava was entering the ocean. Later that evening, the tremor, or ground shaking associated with magma movement, dramatically decreased at Pu'u 'O'o, and the summit region of Kīlauea began to swell with magma as the eruption paused.

On Tuesday morning, active flows could not be found anywhere on the flow field. This situation continued until Wednesday about noon, when new flows were spotted at about the 2,100-foot elevation, indicating that the pause was over.

On Friday morning, these channeled 'a'a flows had advanced down to the 500-foot level on Pulama Pali. The open channels and rapidly moving 'a'a flows could be easily seen from the end of Chain of Craters Road. In addition, a small flow lobe was advancing down the west side of the flow field and burning ohia forest.

Since that time, neither the Lae'apuki tube nor the tube that had recently developed along the east edge of the flow field have been reoccupied, so no lava has entered the ocean since last Sunday. Interestingly, the pause was marked by nearly normal eruption-level tremor, apparently caused by magma movement within the lava pond inside the Pu'u 'O'o cone. The summit swelling also slowed rapidly and was barely noticeable by the time the eruption recommenced on Wednesday.

During the period when the summit swelled with additional magma, many small earthquakes occurred beneath the summit region; these small earthquakes are caused by rock breaking as magma is added to the summit reservoir. During the week, numerous deep earthquakes and tremor that are associated with magma migration up into the volcano were also recorded.

We have identified a possible cause of these brief pauses in the eruption by careful examination of the summit tilt and tremor records. Before each of the last four pauses, deflation and tremor occurred at the summit for a period of about an hour before the pause began. These same signals accompany magma intrusions (underground emplacement of magma into the rift zones) and the onset of new eruptions, although then the tremor is much stronger and the deflation of the summit is much larger. We think that small intrusions of magma occurred before each of the last pauses.

This slight decrease in pressure beneath the summit is enough to shut down the eruption. If this is the case, each of the most recent pauses was triggered by an abortive attempt at a new eruption else where onthe volcano. Some previous pauses were clearly related to major intrusions of lava into the upper east rift zone. In particular, an earthquake swarm in March 1992 near Devil's Throat and a second one in February 1993 near Makaopuhi Crater were caused by much larger intrusions of magma into the upper east rift zone.

NASA's Deformation Image

We had a hectic day on Friday, responding to an erroneous news release issued by NASA and widely distributed by local television and radio stations. Their release indicated that parts of Kīlauea are moving at rates of one foot per year, that such rapid movement might lead to large earthquakes or even giant landslides of the south flank of Kīlauea in the near future, and that a major area of Kīlauea's southwest flank was bulging upward and might be the site of a new eruption.

These reports are all erroneous.

As we discussed in last week's "Volcano Watch," we routinely measure the rates of movement of Kīlauea's south flank (and every other part of the volcano) and are currently measuring maximum rates of about 2.5 inches per year. The large landslides referred to have occurred in Hawaii in the geologic past, but have a recurrence interval of several hundred thousand years. Earthquakes are a constant threat on Hawaii, as has been outlined numerous times in previous "Volcano Watch" columns.

The NASA data do not provide any reliable information to suggest we are closer, or farther, from the next large earthquake.

Finally, the region that the NASA scientists infer is bulging with magma and might be the site of a future eruption shows no signs of magma movement. Rather than bulging upwards, the surface in this area is moving down and towards the coast, but at only moderate rates.The news reports led some listeners to incorrectly conclude that there was a new eruption along the southwest rift of Kīlauea Volcano.

The U.S. Geological Survey's Hawaiian Volcano Observatory monitors Kīlauea and Mauna Loa Volcanoes 24 hours per day with an array of instruments. We report any significant changes in the volcanoes through timely press releases and through this column so that the public will be well informed at all times.