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Mount Etna Just Started Erupting From A New Fissure. Here's Everything You Need To Know

Robin Andrews
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Opinions expressed by Forbes Contributors are their own.
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According to new reports, Mount Etna – an active and mercurial volcano in Sicily – has produced a fresh eruption from a brand-new fissure.

The Etna Observatory, part of Italy’s National institute of Geophysics and Volcanology (INGV), explain that a collection of 130 tremors at the volcano, perhaps indicating magma moving through the crust, caught their attention, with the most powerful of the swarm equivalent to a magnitude 4.0 earthquake. Then, sometime on Monday, lava flows began emerging from a new fissure high up on the southeastern side of the volcano, producing a persistent ash cloud.

So far, it looks like no-one’s in danger, as the flank eruption is taking place high up away from any population centres. Hikers are also being brought down from higher elevations too, according to the Washington Post. Catania's airport has also been temporarily shut down and flights have been grounded in order to not run into trouble with the ash cloud.

So, What Happened?

The Etna Observatory, part of Italy’s National Institute of Geophysics and Volcanology (INGV), explain that a collection of 130 tremors at the volcano, perhaps indicating magma moving through the crust, caught their notice when it began at 0850 hours local time, with the most powerful of the swarm equivalent to a magnitude 4.0 earthquake.

Then, sometime later on Monday, at around 1205 hours, lava flows began emerging from a new fissure high up on the southeastern side of the volcano, producing a persistent ash cloud. According to Boris Behncke, a volcanologist at the Etna Observatory, this is the first flank eruption at Etna for more than 10 years at the site. It began shortly after noon, local time.

At the same time, eruptive activity at various other parts of Etna, including the Northeast Crater and the Bocca Nuova area, amped up a little. GPS networks, among others, found that there has been conspicuous deformations of the summit area,” according to an INGV press release.

This flank eruption appears to be part of a sequence that started in September 2013, according to the Smithsonian Institution’s Global Volcanism Program (GVP). Focused on the New Southeast Crater, these eruptions have not, in general, proved to be dangerous, but the emergence of a new fissure has certainly got the INGV sitting up and paying close attention.

Reporting by Volcano Discovery notes that the lava is flowing into the upper Valle del Bove, a horseshoe-shaped depression feature on the eastern part of the volcano. The new fissure itself appears to be at the foot of the New Southeast Crater.

Early on Wednesday, as the flank eruption continued, an earthquake coming in at a magnitude 4.8 hit part of the volcano just a little southeast of the majority of the activity on Etna. As with the rest of the quakes in this sequence, this was likely caused by the movement of magma through the crust, causing parts of the volcano to fracture in a somewhat dramatic fashion.

At the time of writing, the swarm contains at least 3,000 individual events, most of which aren’t powerful enough to be felt by people. This event, however, was powerful enough to cause some structural damage to buildings in the area, and injure approximately 30 people.

What is Mount Etna’s History Like?

Mount Etna is a particularly strange volcano with a very complex volcanic history. Although it’s a stratovolcano, which is typified by explosive eruptions, it is also capable of producing prolific lava flows too, and the underlying geochemistry of its magmatic system is fairly enigmatic. It has multiple active vents, and a horseshoe-shaped cauldron-like feature named Valle del Bove on its eastern section.

It’s also capable of producing violent magma-water interactions through a style of volcanism known as phreatomagmatism, which you may remember almost killed a BBC film crew near the summit back in 2017. It’s cropped up in the news a fair few times since 2014, as its fantastic plumes of ash, triggered by moderate blasts at one of its summit vents, generate a decent amount of dramatic volcanic lightning.

The 3,329-metre (10,900-foot) high edifice, which also has a base circumference of 150 kilometres (93 miles), has erupted plenty throughout the past year or two, but it’s been active for a considerably length of time. According to the GVP, Etna began to be built between 500,000 and 350,000 years ago, and LiveScience notes that the first historical documentation of an eruption there was written by one Diodorus Siculus in 425 BCE.

A 2018 review by various scientists, including those at the INGV, provided some fascinating detail as to the evolution of Mount Etna using a variety of techniques. Volcanism indeed began 500,000 years ago through submarine eruptions. Then, 300,000 years ago, fissure-style eruptions – think Kilauea’s recent fissures – appeared on land, creating a plateau.

From 220,000 years ago, eruptions along the Ionian coast ended up producing a shield volcano, a massive, far-wider-than-tall volcano a bit like Hawaii’s Kilauea. Then, a shift occurred: around 129,000 years ago, volcanism migrated west towards the current centre of the volcano, and eventually two complex volcanic mounds appeared on the site, fed by various magmatic sources.

There’s some debate as to what exactly is fuelling all this volcanism, but for most of its history, it appears to be linked to extensional tectonic activity. That describes a situation involving the pulling apart of the underlying crust and upper mantle, allowing hotter mantle material to rise up in place and cause considerable melting as it decompresses.

Today, unlike plenty of nearby volcanoes – say, Stromboli and Vesuvius – it doesn’t lie directly atop the subduction zone boundary where the African tectonic plate, along with the Ionian microplate, are descending beneath the Eurasian plate. This setting produces highly explosive volcanism and “evolved” magmatic compositions that have been through a complicated plumbing system and have been cooked and reduced, in a manner of speaking, over time.

Instead, Etna sits just in front of the subduction zone, and doesn’t appear to tap such complicated magma reservoirs. In fact, its fairly fluid magmas are compositionally similar to those you’d see at mid-ocean ridges, despite the fact it sits on continental crust. This 2018 paper in Nature suggests that it’s sucking up lower mantle material from underneath the African plate, which implies that the two doomed, descending tectonic slabs are rolling back a little, creating a stream of superheated mantle material that’s flowing towards Etna.

A detailed dive into its origins is a story for another time, but the TL; dr of this is that Etna is a very complicated volcano, which can make understanding its hazards somewhat difficult.

Its most infamous historical eruption took place in 1669. First, an earthquake triggered by the volcano killed 1,500 people in the town of Nicoli. Then, as lava flowed downslope, the people of Catania dug trenches in order to try and divert it. They succeeded to an extent, but the lava was now heading towards another town, Paterno. A brawl of sorts ensued, and ultimately the lava made it to Catania. Reports are hazy on the damage, but it seems as if plenty of the town was burned down.

Several other hazardous eruptions have happened since and can be divided into two broad categories: summit eruptions, and flank ones. Those at the summit are really only dangerous for those at the peak, but flank eruptions can occur lower down, near population centres – and it’s worth noting that roughly a million people live on the slopes of Mount Etna. That’s why it’s an incredibly hazardous volcano, and one that’s heavily monitored by the INGV.

Flank eruptions, like this one, tend to involve lava effusions, a bit of lava fountaining – when pockets of gas cause burp-like blasts, flinging lava skyward – and plenty of ash generation. They are not majorly explosive, but the hazard here comes in the form of the lava, which is hard to stop. In the past, concrete blocks, trenches and even explosives have been used to try and divert the lava flows, and they often fail to achieve their objectives.

There is also a long-term risk of flank collapse at Etna. Remember what happened at Anak Krakatau? There is a distinct possibility that it’ll happen one day at Etna, and we know this because scientists suspect it happened before: a large tsunami generated by a landslide 8,000 years ago splashed onto the nearby shores of the Mediterranean Sea.

A couple of recent studies also point to the fact that Etna is, by and large, slowly sliding into the sea, driven by gravity more than anything else, although magmatic injections certainly play a role too. There’s no way to tell when a flank collapse could happen but quantifying its movement and understanding how it’s propagating seawards is vital to comprehend its hazards.

Importantly, this flank eruption is unrelated to this type of hazard; there’s zero signs that a flank collapse is nigh, so let’s nip that one in the bud right now.

What Is This Not Related To?

This eruption at Etna has nothing to do with what’s happening in Indonesia, for some many reasons. The fact that Anak Krakatau triggered a tsunami after a multi-month-long eruption sequence (which is still continuing) and the fact that Mount Etna opened up a new fissure on its flanks are entirely coincidental. If you see anyone telling you that there’s a pattern here, please pay them no heed.

It’s also worth remembering that a very active volcano erupting isn’t that unusual. Sure, the appearance of a new fissure is interesting, but Etna is known for erupting fairly frequently. There are also 40 volcanoes, on average, erupting on Earth at any given moment, so don’t think this eruption is the start of something bigger, so to speak. There are no patterns here.

Saying that, it's unclear how the eruption will proceed, so all eyes are on Etna's slopes, even on Christmas Eve.

This is a developing story, and will be updated as more information comes in.

Robin Andrews
Robin Andrews
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