The Big Island of Hawaii is famous for its quietly erupting volcano, Kilauea. Thousands of people each year walk up close to the sluggish rivers of lava that have oozed down the volcano’s slopes, and often into the sea (above), since 1983. There’s even a visitor center at the summit.

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As it turns out, Kilauea has been giving people the wrong impression. A new assessment of Kilauea’s past activity suggests that this gentle giant’s current mood is a calm lull between aggressive tendencies. In fact, the volcano has erupted explosively about as often as Mount St. Helens.

“Though the explosions may be smaller, there are a lot more people in the area, so the risk is very high,” cautions Don Swanson, a geologist with the Hawaiian Volcano Observatory. “So we have to be very concerned.”

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Kilauea’s next mood swing is likely to last for centuries, Swanson says. New carbon dating of the remnants of old eruptions indicates that the volcano was explosive for 60 percent of the past 2,500 years. It just happens to be in one of its more peaceful, lava-flow stages at the moment.

Swanson announced these latest results during a news conference Tuesday at the annual fall meeting of the American Geophysical Union in San Francisco. This isn’t the first time he has pointed out Kilauea’s explosive history, but it is the first time anyone has shown the length of time the explosive periods lasted.

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For years Swanson has been gathering evidence about and alerting the public to Kilauea’s dark side. In a T.V. interview earlier this year, he described the threat:

“The most dangerous part of the explosions is something that is probably least known to people, and that is fact that they can produce clouds that are a mixture of hot ash and gases that can move horizontally across the ground surface at very rapid speeds—hurricane velocity.”

Searing hot ash and gas suddenly surging out of the volcano killed several hundred people in November 1790, according to rough historical estimates, making Kilauea the deadliest volcano active in the United States today.

Swanson says he is certain that this kind of surge will happen again, engulfing much of the volcano’s summit and spreading ash around the entire island. Yet he offers some comfort: such an event would probably be preceded by a dramatic sinking of the crater at the volcano’s summit, which would unfold over the course of several days—providing time to evacuate. Only there could be no going back for centuries.


This violent, early-morning explosion of steam, rock, and ash ignited as a sluggish river of hot lava from Kilauea volcano entered the Pacific Ocean, causing near-instantaneous evaporation of seawater. (Photo courtesy Susan Dieterich)

A night-time exposure of the fume cloud from Halemaʻumaʻu, a lava-filled crater near Kilauea’s summit. The Milky Way is clearly visible in the sky above. (Photo courtesy James Dieterich)