Holy hell, Batman: Mount Etna’s sliding toward the sea! This may sound fairly dramatic, but don’t worry, everyone. Europe’s most (in)famous volcano is indeed on the move, but at an average rate of just 14 millimeters (0.55 inches) per year, about three times slower than the average growth rate of your fingernails. Don’t expect the mountain to literally topple into the sea anytime soon.
There’s plenty we’re still yet to understand about Mount Etna, easily one of the most dangerous volcanoes in the world. Its “fuel” source remains somewhat enigmatic, and just recently, a controversial paper implied that it’s a gigantic hot spring, and not even a proper volcano – a rather provocative claim to say the least.
The latest revelations about this fiery fountain may also sound fairly bonkers, but the idea itself isn’t new or unusual. “Geological field evidence and laboratory modelling indicate that volcanoes constructed on slopes slide downhill,” the Bulletin of Volcanology paper notes.
The difference this time is that the Open University-led team has directly detected the movement, or “basement sliding”, of the entire edifice of an active volcano for the first time.
The team suggest that the occasional inflation of Etna’s magma chamber prior to eruptive activity, as well as the more dominant “gravitational spreading” – the lateral extension and vertical contraction of a massive geological object over time – are potentially to blame for the volcano’s sneaking here.
Either way, it’s able to slide even on a very slight (1-3°) slope because the sediments on which it’s based, including clays, marls, limestones, and sandstones, are poorly consolidated, like a pile of inedible crumbs. Etna is, in a manner of speaking, very slowly surfing seawards.
Intuitively, it makes sense that big things on a slope will slide downhill, even if they’re utterly enormous and attached to the slope on which they’re sliding. Detecting this movement, however, is quite difficult when said gigantic, frequently erupting edifice is moving so very slowly.
“Much bigger movements occur on active volcanoes during eruptions – I once measured a horizontal movement of more than 4 meters [13 feet] at one point on Etna – which have swamped the signal of the downslope movement,” lead author Dr John Murray, a renowned expert on Etna at the Open University, told IFLScience.
Fortunately, Etna is covered in a network of hundreds of GPS kits, which can detect the slightest movements between eruptions. Between 2001 and 2012, they revealed that the entire edifice is generally moving toward the east-southeast, into the Mediterranean Sea, at the aforementioned rate.
As the study authors also point out, “it is a continual battle to replace benchmarks as they are destroyed by eruptive activity.” It’s likely several other volcanoes are on similarly slippery slopes around the world too, including Mexico's Colima. No other volcano on Earth is smothered in quite as many GPS devices as Etna, however, so proving this may be difficult.
So – what does Etna's seaward journey mean for us feeble humans, in the long run?
“I don’t think that there’s anything to worry about at present, and probably not for hundreds or thousands of years ahead,” Murray said, adding however that “the geological record shows that extinct volcanoes built on slopes, which were sliding during their lifetime, have had catastrophic collapse later in their history.
“If it increases significantly in the future, then we may have something to worry about, but if it stays the same” – as Murray suspects it will – “then I think the Sicilians can sleep safely in their beds.”
