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January 7, 1999

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


How long do eruptions last?

Kilauea has been erupting for more than 16 years. Is this an exceptionally long time for an eruption to last? The answer is yes, but there have certainly been longer eruptions during human history--much longer.

Stromboli, one of the Eolian Islands north of Sicily, is the undisputed champion. Known as the "lighthouse of the Mediterranean" by Roman and Greek sailors, Stromboli has apparently been erupting almost continuously for more than 2,400 years. A climb up the easy trail to the top of Stromboli will almost certainly reward the visitor with views of spattering from one or more small vents. Nighttime views are particularly colorful, and the Roman-candle show of glowing spatter arcing through the night air reminds a Hawai`i resident of New Years Eve without the sounds and smell of gunpowder. Rarely, however, does Stromboli do more than emit spatter. Lava flows, moderately high fountains, and even steam-driven explosions have been witnessed, but they are not the norm.

According to the catalog "Volcanoes of the World" by Smithsonian Institution volcanologists Tom Simkin and Lee Siebert, 9 percent of eruptions end in less than one day, 16 percent within two days, 24 percent within one week, 30 percent within two weeks, 43 percent within a month, 53 percent within two months, 83 percent within a year, and 93 percent within three years. Thus Kilauea's current eruption is in the top 7 percent of the 3,211 historical eruptions examined by Simkin and Siebert. It is halfway toward achieving what only 0.5 percent of those eruptions have--a duration of 30 years or more.

The ongoing eruption still has to catch up with at least two past Kilauea eruptions. Most of Puna north of the east rift zone was covered by lava flows during what appears to have been a sustained eruption in the first half of the 15th century. Lava from this event, dubbed the `Aila`au eruption, came to the surface from a low shield east of Kilauea Iki and eventually flowed eastward and northeastward into the sea at Kaloli Point. Some lava, perhaps from the same eruption, moved southward to form the youngest flow on `Ainahou Ranch.

The best estimate for the duration of the `Aila`au eruption is 40-50 years, based on radiocarbon ages obtained and interpreted by Dave Clague (formerly of HVO). This estimate is probably a minimum, for some late flows could have covered earlier, unvegetated lava flows of the same eruption; such late flows would be impossible to date by radiocarbon methods, which depend on charcoal from burned vegetation. So, Pu`u `O`o has to continue for at least another 25 years and perhaps longer to match the duration of the `Aila`au eruption.

Pu`u `O`o faces an even tougher challenge. Halema`uma`u and other vents on the floor of Kilauea's caldera were continuously active for at least 71 years, from 1823 until 1894. For the next 30 years, Halema`uma`u was mostly active, though with pauses long enough to disqualify it as a continuous eruption.

Another possibly long-lived eruption built Kane Nui o Hamo, on Kilauea's east rift zone, more than 700 years ago. Sparse evidence suggests that this eruption, which produced a flow field comparable in size to that of the current eruption, lasted more than 50 years.

Given the choking vog of the new year, residents of East Hawai`i doubtless wince at the thought of the current eruption lingering for another several decades. We have no evidence that it will or that it won't, but the past history of Kilauea suggests that it might. No matter what, however, the Pu`u `O`o-Kupaianaha eruption already is exceptionally long by even world standards, and it becomes even more exceptional with each passing day.

Eruption Update

The eruption continues at its usual pace, unbroken by the onset of 1999. Lava continued to erupt from Pu`u `O`o and flow through a network of tubes from the vent to the sea. No surface flows from breakouts of the tube system were observed on the coastal flats. Lava is entering the ocean near Kamokuna and forming a new bench. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the new land. The steam clouds are highly Pnd laced with glass particles.

The poor air quality continued in East Hawai`i during the past week, as the kona winds carried the volcanic gases into populated areas that are usually upwind of the vents.

Two earthquakes were reported felt during the past week, ending on January 7. Residents of Leilani Estates reported one tremor at 7:18 p.m. on New Years Eve. The earthquake originated at a shallow depth south of Pu`u Kaliu and had a magnitude of 2.5. At 5:45 p.m. on Wednesday, January 6, residents of Hawaiian Ocean View Estates were jolted by a magnitude-3.7 earthquake, located about 15 km (9 mi) northwest of Na`alehu at a depth of 9 km km (5.5 mi). One earthquake felt in Leilani Estates on December 27 was overlooked in last week's report. It was fairly large, a magnitude 4.7, but was located at a depth of 11 km (7 mi) south of Apua Point and so was not widely felt.

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Updated: 21 Jan 1999