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Etna Volcano Becoming Dangerous, Experts Warn

Hillary Mayell
for National Geographic News
February 6, 2003
 
The current eruption of Sicily's Mount Etna, which began on October 27 of last year, has officially ended, according to volcanologists at the Instituto Nazionale di Geofisica e Vulcanologia (INGV).

That's the good news.

The bad news is that the eruptions that took place in 2001 and 2002-2003 were two of the most explosive of the last several centuries, and that pattern is likely to continue, said a team of four volcanologists with Italy's volcano research agency.

Writing in the February 6 issue of the journal Science, Domenico Patanè and colleagues report that the intrusion of a huge volume of magma into the volcano beginning in 1994 is likely to make Etna's reputation as the "friendly giant" a thing of the past, with eruptive activity becoming more frequent, voluminous, and potentially more hazardous in the near future.



"The intensity of the 2002 eruptions, and the fact that this occurred so closely in time to that of 2001, is the result of the presence of a magma rich in gas added to the volume intruded before the July-August 2001 flank eruption," said Patanè. "The volcano has been intensely fractured during the 2001 and 2002 flank eruptions; this in the future might allow magma easily to rise at the surface."

Europe's Tallest Volcano

Etna is one of the world's most active volcanoes, having been in a state of near-continuous eruption for half a million years. Documentation extends back to 1500 B.C. Etna's eruptions have caused very few deaths—hence its friendly-giant reputation—because the lava flows are slow, the eruptions are not particularly explosive, and preceding earthquakes usually give local residents plenty of warning.

The July-August 2001 eruption was unusual not only for its explosiveness, but also because eruptions occurred simultaneously on the volcano's flanks and at its summit. However, Patanè says it was too short to allow a complete emptying of the intruded magma.

The 2002-2003 eruption was also unusually explosive, hurling lava and ash at a velocity of 350 to 450 meters per second (800 to 1,000 miles per hour) from the main crater and also from at least nine new craters that opened in the mountain, according to the European Space Agency. The volcano also belched an enormous amount of sulfur dioxide into the atmosphere.

One of the most geologically complex volcanoes on Earth, Etna has four summit craters and more than 250 cinder cones on its flanks. Some of the cones are so large they would be ranked as volcanoes in their own right in other regions, said Boris Behncke, a volcanologist at the University of Crete. And the volcano is constantly evolving.

"The 2002 eruption has been described in many reports as a highly unusual event for Etna, and really, this eruption has been one of the most explosive flank eruptions of this volcano in recent times," said Patanè. "The majority of the total volume of erupted products is pyroclastics [particles and rocks ejected from a volcano during eruption], contrasting with most recent eruptions of Etna which produced mainly lava effusion [flowing over the ground]. However, it is very far from the explosivity of some prehistoric and historic Etnean eruptions, like those which have generated the large pyroclastic cones distributed on the lower flanks of the volcano."

Monitoring Mount Etna

To study the recent changes at Etna, the four Italian volcanologists looked at data surrounding 647 earthquakes that occurred between 1994 and 2001. They suggest that the activity of the last several years provides evidence that beginning in 1994, a huge amount of magma pushed its way into Mount Etna's central plumbing system through an area below sea level where two fault lines intersect.

"A more or less continuous transfer of magma from the volcano's storage reservoir located at six to 15 kilometers (four to nine miles) depth into a shallower (three to five kilometers/two to three miles) magma reservoir also occurred during 1994-2001, allowing magma to accumulate in the upper part of Mount Etnas plumbing system," said Patanè.

"The increasing volume of stored magma created an enormous amount of pressure on the rocks above, triggering most of Etnean earthquakes that occurred between 1994 and 2001," he said. "The overpressure of this shallower storage zone, caused by magma accumulation, triggered the eruptions that took place in 2001 and 2002."

What caused the sudden infusion of magma is unknown.

"The mechanisms and timing of intrusions of magma from the mantle are an area of ongoing study," said Wendy Bohrson a geologist at Central Washington University who has studied Etna. "Modeling and laboratory studies have contributed greatly to our understanding, but volcanologists still have a great deal of work to do to fully describe the exact conditions that control the size and timing of intrusions from the mantle."

Monitoring of the volcanic activity at Mount Etna has become much more sophisticated since 1989, allowing researchers to track in nearly real time sub-surface magma movements, said Patanè.

"At present, the Catania Section of the Istituto Nazionale di Geofisica e Vulcanologia has a multidisciplinary monitoring system which allows us to recognize well in advance any significant signal of a new impending eruption. This allows us to advise the Civil Protection authorities with months to days in advance of an impending eruption," he said. "However, the size of an eruption still remains an open question.

"The volcano is erupting more frequently now than during the previous three centuries, and magma output rate is increasing. At present, there is no reason to hypothesize that this trend will invert in the near future. Therefore, in the future, flank eruptions must be expected to occur at intervals ranging from one to three years, and some of them might be much more voluminous and probably explosive than in the past."
 

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