As if Sicily's Mount Etna hasn't been enough of a nuisance this summer, it now emerges that the volcano has been going through something of an identity crisis that could make it more prone to acts of random violence.
Over the past hundred thousand years or so - a geological heartbeat - Etna may have gone from placidly dribbling fluid magma to violently ejecting clumps of lava. So suggests a new analysis of rocks expelled by the volcano
"It's the first time this kind of transition has been seen," says Pierre Schiano of Blaise Pascal University in Clermont-Ferrand, France, who led the study. "Now we can explain lots of Mount Etna's curious features."
Geologists have long wondered about Etna's split magmatic personality. Its location suggests it should be a hot-spot volcano like those found in Hawaii. Such volcanoes are produced by a column of pure magma forced up to the surface from deep in the Earth.
But the lava ejected by Etna is closer to that produced by island-arc volcanoes. These form when a watery slab of the Earth's crust, thrust below another slab by tectonic movement, melts, forcing magma to burst through the surface. Huge steam pockets cause an erupting island-arc volcano to belch lava explosively and dangerously. The Philippines are home to many classic island-arc volcanoes.
The magmas from these two types of volcano contain different amounts of trace elements such as barium and neobium. Screening these chemical signatures in rocks from eruptions over the past 500,000 years, Schiano's team shows that Etna, once a hot-spot volcano, is now more like the island-arc variety.
Trace elements change as magma nears the Earth's surface. So the researchers searched the rocks for minute melt inclusions: glass beads, the width of a human hair, that preserve the original magma in its pristine state, Schiano explains.
What drove Etna's transformation is less clear. Probably the southward movement of crust below an island-arc region of the Mediterranean - the Aeolian arc - towards Etna, is now driving the volcano.
"It's speculation, but it's reasonable," says melt inclusion researcher Adam Kent at the Danish Lithosphere Centre in Copenhagen. "There has to have been a fundamental change in the magmatic plumbing system beneath Etna."
If the transition continues Etna could, over the next few thousand years, become more dangerous as it begins to behave more like a classic island-arc volcano with violent explosive eruptions.