June 6, 1997

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

Friendly Kilauea

What volcano in the United States has been the most deadly since the country was founded? Mount St. Helens? Mount Rainier? Lassen Peak? Good guesses; but wrong. Don't feel bad, though. Many volcanologists don't know, either. You get an HVO Gold Star if you answered Kilauea. Kilauea?? The drive-in volcano that destroys property but spares lives? The volcano that annually attracts 2.5 million visitors hoping to see an eruption? Friendly Kilauea? Yup, the same one.

Kilauea has killed at least four in this century. A visitor ventured onto the seacoast bench in 1993 and was swept away when the bench collapsed. A photographer was killed by falling rocks blasted from Halema`uma`u in 1924. Kilauea's toll also includes deaths from earthquakes, which are ultimately related to volcanic activity. Two campers died at Halape in 1975 during the tsunami that followed a large earthquake generated within Kilauea.

Forty-six people perished along Kilauea's coastline in 1868, when a huge earthquake caused widespread shaking, coastal subsidence, and a tsunami that destroyed several villages. Thirty-one died in a landslide in Wood Valley, and two in rock falls in Hilo. Whether this earthquake was centered within Kilauea or Mauna Loa is debated, but its effects on Kilauea were devastating.

The single largest catastrophe, by itself making Kilauea the answer to the question posed earlier, resulted from an explosion from the caldera in about 1790. Estimates of the number of fatalities range from "about 80 warriors" (William Ellis) to about "400 people" or "800 warriors" (Stephen Desha) to "5405 countrymen" (David Douglas, quoting an eyewitness, a Priest of Pele, in 1834). The lower numbers are probably most realistic. The dead were warriors and family members of Keoua's army bound for Ka`u. They were probably killed several kilometers (miles) southwest of the present site of HVO. Corpses were discovered clasping one another, perhaps to keep from being blown away by hurricane-force winds accompanying the explosion. The bodies were apparently singed, and death most likely occurred because seared lungs couldn't breath the ash-choked air of the pyroclastic surge, the technical term for this type of explosion.

Recently, geologic studies uncovered evidence for explosive eruptions about 1,100 years ago. Most of their deposits are buried by younger lava flows south of the caldera. Another explosive eruption took place about 2,200 years ago; its deposits underlie Volcano Village and Kilauea's summit area. How many past explosions remain unknown because we haven't found evidence for them? Each known explosion would be lethal today if it were to occur unannounced.

"Unannounced" is the key word. HVO volcanologists believe that such explosions will be telegraphed by precursory activity, probably involving collapse of the floor of Halema`uma`u or another pit crater. Collapse is thought necessary to allow groundwater to enter the magma conduit and heat to steam, which drives the most vigorous explosions. We think (though can't guarantee) that we'll know when explosions are possible, but we'll never be able to pinpoint their exact time or size. Precursory activity will prompt public warnings. HVO, near Halema`uma`u, will be one of the first places evacuated.

Most explosions will come from the summit area, but not all. Any place along the rift zones can collapse and engender explosions. For example, a prehistoric explosion from Alae Crater, near Mauna Ulu, left a deposit plainly visible before lava covered it in 1969. The explosions 1,100 years ago may also have issued from the upper part of the east rift zone.

The gloomy, even macabre, tone of this article is intentional, to impress readers that volcanoes may be great places to visit, inhabit, and enjoy, but that risks are inherent. Sooner or later something untoward will happen. Kilauea provides ample evidence of this unfortunate truth.

Kilauea Eruption Status--June 6

Kilauea's east rift zone eruptive activity continued during the past week. Early in the week, vents on the southwest flank of Pu`u `O`o fed flows that traveled up to 1.5 km away from the cone toward the southeast. As activity from the southwest flank vents waned, a vent on the west flank of Pu`u `O`o restarted early Wednesday morning and fed a flow moving to the northwest. This flow has reached the forest and is burning trees within the National Park. Occasional fountains up to 40 meters high were observed from the western vent.

Recent Big Island Earthquakes

The swarm of shallow earthquakes located beneath the Namakani Paio campground in Hawaii Volcanoes National Park has greatly diminished. Six temblors were felt in the Kilauea summit vicinity on Monday and Tuesday, and over 400 earthquakes were recorded.