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March 21, 2002

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

The most active volcano on Earth?

From time to time, we get calls from people who are writing about Kilauea, hoping to confirm the idea that Kilauea is the most active volcano on Earth. We have to tell them that, no, it's only one of the most active volcanoes. At least one other volcano on the planet erupts more frequently than Kilauea - Stromboli. Stromboli Volcano, off the west coast of southern Italy, has been erupting nearly continuously for over 2,000 years. Often called the "Lighthouse of the Mediterranean," Stromboli produces spectacular incandescent explosions that have long attracted visitors.

A typical eruption at Stromboli consists of several small gas explosions each hour, ejecting incandescent cinder, lapilli, and bombs to heights of a few tens or hundreds of feet. Tephra is glowing red when it leaves the vent but becomes black and nearly solid before hitting the ground. Occasionally, lava flows may also be produced. Lava flows from Stromboli are typically less fluid than Hawaiian lava flows and thus are somewhat shorter and thicker. Because of the lower fluidity, it is harder for gas to escape from the rising magma. Gas bubbles become pressurized and burst at the top of the magma column, producing small explosions and throwing clots of molten lava into the air. When this type of eruption is observed at other volcanoes, it is referred to as "Strombolian".

Volcanic activity is often classified by its resemblance to the type of eruption common to a specific volcano. Eruptions characterized by quiet effusion of fluid lava with low gas content and high temperature are called "Hawaiian". However, during some Hawaiian eruptions (such as the early episodes of the current Pu`u `O`o eruption), gas pressure in the magma propels lava high into the air. These lava fountains are not truly explosive and are best thought of as jets of incandescent lava shot into the air like water from a fire hose.

Further examples of eruption types are Vulcanian (after Vulcano, Italy) and Peleean (Mt. Pelee, Martinique, West Indies). Vulcanian eruptions commonly involve relatively cool, thick, gas-rich magma. This type of eruption usually begins with steam explosions that remove old, solid material from the central vent. A cauliflower- or mushroom-shaped cloud of ash, often with lightning within it, then develops above the vent. The eruption of thick, sluggish lava flows indicates the end of the eruptive cycle. Peleean eruptions are characterized by the formation of domes and powerful, glowing avalanches of hot ash and blocks that travel down the flanks of the volcano.

Another type of eruption, Plinian, is named for a person rather than a volcano, though which person may not be completely clear. Pliny the Elder was a Roman naturalist who died in the A.D. 79 eruption of Vesuvius volcano, while his nephew, Pliny the Younger, made detailed observations of the eruption. Plinian eruptions, like the Vesuvius eruption, are large, explosive events that send enormous columns of ash, pumice, and gas high into the stratosphere. Pyroclastic flows and extensive ash fall are usually produced during these events as well. Recent examples of Plinian eruptions include Mount St. Helens (1980) and Mount Pinatubo, Philippines (1991).

Additional classifications of eruptions are based on the nature and scale of activity, for example, basaltic flood eruptions and gas eruptions. There are gradations between each type of eruption, and some volcanoes display more than one type of activity.

Although Kilauea cannot lay claim to the title of most active volcano on Earth, it is indeed one of the most active. From at least 1823 until 1924, lava-lake eruptive activity was almost continuous in the summit caldera. Since 1924, only one interval of more than four years has separated eruptions - the 18-year quiescence between 1934 and 1952. The current eruption has been going on for over 19 years and shows no signs of stopping.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week, and nearly the entire Pu`u `O`o crater floor is covered by fresh lava. Bright glow persists over the "rootless" shield area, where short flows emanate from overflows of the perched ponds and from leaks at the base of the shields. Flows on Pulama pali are mainly crusted over. Surface flows appear on the fan at the base of the pali and extend onto the coastal flats. The distal end of the flows is 2.3 kilometers (1.4 miles) from the seashore.

One earthquake was reported felt during the week ending on March 21, but it was not large enough to be located. skip past bottom navigational bar

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Updated: March 25, 2002 (pnf)