This November, thousands of small earthquakes marked the rise of magma towards the surface along a 14km-long fracture near Iceland's Svartsengi geothermal power plant. Molten rock is now close to the surface and has opened wide fractures that slice through the small town of Grindavik. The ground is still swelling and an eruption could happen with little notice.
At around the same time as earthquakes were shaking parts of Iceland, Sicily's Mount Etna exploded impressively, dumping ash on nearby towns.
That's not all. Elsewhere, 45 other volcanoes across the world continue to rumble, including Mayon and Ta'al in the Philippines, Santa Maria in Guatemala, Nevado del Ruiz in Colombia and Krakatau in Indonesia. Of these, the latter is building again following a collapse in 2018, which created a tsunami that took more than 400 lives.
How active are these volcanoes?
It is possible that the rising magma near Svartsengi may not erupt at all, merely solidifying beneath the surface instead. But if it does, it is likely to be in typically Icelandic style – very fluid lava will pour from long cracks in Earth's surface, occasionally solidifying into spectacular cones.
At Mount Etna, the recent eruption marks business as usual at a volcano that is always sparking minor firework-like displays, pumping out lava, or launching columns of ash high into the atmosphere.
Activity at the rest of the world's currently active volcanoes is – at the moment at least – relatively inconsequential, involving minor explosions, lava outbursts or the formation of small pyroclastic flows (rapidly moving flows of hot ash and gas). The only threat is to those living on or close to the volcanoes, so many have exclusion zones in place in case activity escalates.
Why are all these volcanoes erupting?
Volcanoes erupt when fresh magma produced in the Earth's mantle reaches the surface, either via an open vent or by breaking the rock above it.
This actually happens all the time, with about 70 volcanoes erupting every year – of these, around 20 erupt each day. Iceland has an estimated 30 volcanic 'systems', discrete zones where an eruption can occur, either from an established cone or from new fissures (cracks in Earth's surface).
In fact, Iceland – which straddles the join between the North American Plate to the west and the Eurasian Plate to the east – is built entirely from volcanic rock.
The plates are moving apart at about the same rate as your fingernails grow, allowing new magma to rise and feed eruptions that happen somewhere on the island every few years. Elsewhere, many of the currently active volcanoes are located above so-called subduction zones, where one tectonic plate is diving beneath another.
As the subducting plate pushes further into the Earth, it begins to melt, sweating out the magma that feeds the volcanoes above. Typically, these magmas are stickier and more gas-rich than those that erupted in Iceland – and they can feed far bigger, explosive, and deadlier eruptions.
Has this volcanic activity happened before?
In 2021, Iceland's Fagradalsfjall volcano erupted after a long period of dormancy, putting on a spectacular show just 40km west of the capital Reykjavik. It was the first time for more than 800 years that an eruption had occurred in the Reykjanes Peninsula, and the region may now be the source of new eruptions for decades to come.
Etna, on the other hand, is never quiet. But its past activity has been far more destructive. The main problem has come from lava outbursts low down on its slopes, which caused considerable damage through inhabited areas in 1928, 1971 and 1983. Further back in time, an enormous lava eruption in 1669 destroyed parts of the coastal city of Catania.
Many of the volcanoes currently displaying low-level activity have also had far bigger eruptions, most notably Krakatau, which killed 36,000 people in a colossal explosion in 1883. Then there's Nevado del Ruiz in Colombia, which took 23,000 lives in 1985. And in 1902, Santa Maria (Guatemala) hosted one of the biggest volcanic blasts of the 20th century, killing around 6,000 people.
Should we be worried about volcano eruptions?
The short answer is, no more than usual – unless you live in the Icelandic town of Grindavik. The citizens are currently evacuated, and plans are in place to try and protect the town using water jets to cool any lavas heading its way.
A small concern is that a future Icelandic eruption might follow the same pattern as the Laki eruption of 1783. Then, a voluminous outpouring of lava was accompanied by a huge volume of poisonous gas. This formed a noxious cloud that spread at least as far as Europe and eastern North America, polluting the air, bringing extreme weather and causing famine as far afield as Egypt, and perhaps India.
Elsewhere, nothing Earth-shattering is on the cards, but one thing I have learned in four decades of studying volcanoes, is to always expect the unexpected.
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