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."