Volcano Watch — What if there'd been no Pu‘u ‘O‘o eruption?

When the eruption started on January 3, 1983, no one had any reason to suspect it would last into the next millennium. Since 1952, when Kīlauea resumed erupting after a lull of 18 years, the volcano had erupted 32 times. Twelve eruptions started at the summit (Halemaumau, Kīlauea Iki, and the caldera floor). One started at the summit and migrated into the southwest rift zone. Another started at the summit and shifted into the east rift zone. One eruption took place only in the southwest rift zone. The remaining 17 eruptions were confined to the east rift zone.

Twenty-two of these 32 eruptions took place in the 20 years preceding 1983. Thirteen eruptions started in the east rift zone, one in the southwest rift zone, and six at the summit. The two others started at the summit and migrated into one of the rift zones.

These tallies indicate that about 53 percent of the eruptions since 1952, and 59 percent since 1962, started on the east rift zone. Forty-four percent of the eruptions since 1952, and 36 percent since 1962, started in the summit.

The average length of time between the onset of eruptions was about 1 year, for both the 1952-1983 and 1963-1983 periods.

Thus, in the 20 years since 1983, we might have expected--statistically, at least--20 different eruptions, 55 percent (11) in the east rift zone, 40 percent (8) that started in the summit, and perhaps one in the southwest rift zone.

Of the 17 eruptions in the east rift zone between 1952 and 1983, two took place from fissures that cut through lower Puna, one in 1955 and the other in 1960. Two out of 17 is about the same as 1 out of 11. In other words, one of the fictitious 11 eruptions between 1983 and 2003 could have been in lower Puna. Of course, none would have been in lower Puna if the record from 1963 to 1983 were used for comparison.

All of this proves nothing. The statistics are not solid, because the number of eruptions is small and the time interval short. For example, there were few east rift eruptions between 1840 and 1955; using that period would change the statistics greatly. If they are relevant at all, the statistics are good only for the past 50 years of Kīlauea activity.

The tabulation does, however, highlight an important fact about the Pu`u O`o eruption. The past 20 years have been ones of stability at Kīlauea, with far less uncertainty than at any time in the past 50 years.

This stability has helped the island. Development in lower Puna has not had to deal with an eruption, and, as media accounts have stressed, the continued eruption has brought visitors and dollars to the county. Had the eruption not taken place, we would probably have had an on-again, off-again style of volcanic activity difficult to plan around.

When the current eruption ends, we'll probably start looking at the statistics again. Magma may stop entering the volcano for a while; if so, the volcano will shut down as it did from 1934 to 1952.

So long as magma is supplied to the volcano, however, it has to go somewhere. It either intrudes into the edifice, causing potential structural instabilities, or erupts to the surface. About half of the eruptions are likely to occur in the east rift zone, and perhaps 5-10 percent of those will start in lower Puna.

With all these uncertainties, the stability of the current eruption can be viewed as reassuring, despite all the trouble and destruction it has caused. These may be viewed as the "good old days" when the next fissure starts erupting fountains of lava along the lower east rift zone.

Volcano Activity Update

Eruptive activity at the Pu`u `O`o vent of Kīlauea Volcano continued unabated during the past week. Lava flows through a tube system from the vent to the sea. Lava continues to enter the ocean and form lava deltas (benches) at Wilipe`a, West Highcastle, and between Highcastle and Lae'apuki. The east arm of the Mother's Day flow, which feeds the Highcastle-Lae`apuki entry, has persistent breakouts between Paliuli and the coast. A substantial new flow tongue is visible on Pulama Pali and has made it halfway to Paliuli.

The Wilipe`a and West Highcastle lava deltas have hosted several small collapses in the past week, and explosions have been common. The public should be aware that the ocean entry areas can collapse at any time, potentially generating large explosions in the process. The steam clouds rising from the entry areas are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary onto the lava deltas and benches. Even the intervening beaches are susceptible to large waves suddenly generated during delta collapse; these beaches should be avoided.

No earthquakes were reported felt on the island during the past week.

Mauna Loa is not erupting. The summit region continues to inflate, though the rate of inflation has slowed gradually during the past month or two. The earthquake activity is low, with only 2 earthquakes located in the summit area during the last seven days.