Italian News

What Do You Know About Etna’s Eruptions?

By Dr. Alberto Lunetta, NAS Sigonella Public Affairs

Boasting a huge surface of 1,200 square kilometers, the 10,918-foot-high Etna is the largest and tallest volcano in Europe, as well as one of the most active volcanoes on Earth. Around 900,000 residents live on the slopes or in the vicinity of Etna.

Every time the glow of Mt. Etna’s orange halo appears, people get excited, scared, curious, or are simply awed by the spectacle. Traditional media outlets often sensationalize the volcanic events by using dramatic pictures of giant lava explosions and label every pyroclastic blast as a “new eruption,” even though Etna’s eruptions tend to last for months, if not years. Additionally, local volcanologists will often get pressed for predictions about future eruptions, which are impossible to accurately state.

To combat hearsay, local experts try their best to explain to the media what’s really happening to dispel the rumors, but their statements are sometimes misinterpreted.

So, what is the real story behind Etna’s eruptions, and how does the volcano typically behave?

Etna produces two extremely different types of eruptions: summit eruptions and flank eruptions.

Summit eruptions take place in the four craters of the volcano (the North East Crater, the Voragine, the Bocca Nuova, and the South-East Crater) and can go on for months or even years with spectacular lava fountaining and effusive activity which produce abundant ash fallouts. This type of volcanic activity, called “Strombolian,” does not typically pose any danger to local towns except for the ash that can cause traffic hazards, damage to infrastructure and utilities, and acute health effects in the exposed population. Air traffic can also be disrupted by closures of the Catania and local airports.

“As of mid-January 2021, Etna has been erupting for more than 15 months almost without interruption,” said Dr. Boris Behncke, a research scientist at the Catania office of the National Institute of Geophysics and Volcanology (INGV) which monitors Etna 24/7 with 170 stations scattered around the Catania provincial area, keeping an eye on eruptions’ early warnings. “Since early December 2020, the activity has intensified, with several episodes of lava fountaining and lava flow emission from the Southeast Crater (the most active of the four summit craters), and renewed lava emission on the morning of 17 January. Intermittent explosive activity, sometimes accompanied by small lava flows, is also occurring at the Voragine (“big mouth”) crater, and sporadic explosions are taking place at the other two summit craters, the Bocca Nuova (“new mouth”) and Northeast craters.”

Behncke is committed to creating awareness about the risk of volcanic hazard in a highly-populated area. He reiterated that although Etna’s volcanic activity is spectacular, these summit eruptions pose little threat to the people living around the volcano and their property.

In contrast, flank eruptions are characterized by deep magma which emanates from the central conduit and escapes by infiltrating lateral fissures of the volcano at lower altitudes. A flank eruption in 1669 was so large that actually it changed the topography and size of the city of Catania. Thanks to its medieval walls, Catania was spared by the lava that surrounded part of the city, but the lava flows increased the coastline by half of a mile. The Ursino Castle, which used to be a stronghold overlooking the sea, became a land fortress. Although some sources incorrectly conflate this eruption with the terrible 1693 Eastern Sicily earthquake which killed about 12,000 of the 19,000 city residents, no casualties were reported from this flank eruption.

Since 1669, other dramatic eruptions have occurred to include in 1886 near Nicolosi, in 1923 near Linguaglossa, and in 1928 when the city of Mascali was buried by lava. In 1971, another eruption covered the Etna Observatory, destroyed the Etna cable-car, and threatened several villages on Etna’s eastern flank. In 1981, the town of Randazzo was narrowly missed by a new vent which opened near the town’s limits.

As for more recent volcanic activity, another important flank eruption occurred in 1991-1993 and threatened the town of Zafferana. Subsequent eruptions occurring from 1995 until 2009, including the current one, haven’t been particularly dangerous because they are mainly summit eruptions.

When Etna’s eruptions occur, they can trigger earthquakes which may cause structural damage to homes, buildings, and infrastructure. Earthquakes are obviously troubling events and sometimes create confusion among residents and tourists who don’t know where the seismic activity is coming from. About four weeks ago, for instance, Etna was blamed for a 4.6 earthquake occurred off the Ragusa coast, forcing experts to explain that it was not the case.

The good news is that, according to experts, Etna typically generates only small-magnitude earthquakes! Though Sicily’s seismic activity is mainly associated with Etna, many earthquakes which occur across Sicily are due to the island’s complex geodynamic context. Sicily sits atop the convergence of the African and Eurasian tectonic plates. This precarious perch would be the typical reason for a larger magnitude earthquake.

So, as Behnke pointed out, Etna is neither a friendly nor hostile volcano; she’s just a volcano behaving the way a volcano should behave. However, over the past 150 years, the population in Etna’s area has tripled, and residents do need to be informed of the low volcanic risk.

Etna is one of the most active and studied volcanos in the world whose documented history dates back to 475 BC. It was added to the list of UNESCO World Heritage Sites in 2013 for the importance of its geological and scientific features. The volcano produces breathtaking long-lasting and near-continuous eruptions, which are mainly restricted to the summit craters and do not pose threat to the local communities. However, over the centuries, flank eruptions threatened and/or inundated surrounding inhabited areas destroying properties, houses and infrastructures. Etna is constantly monitored by Italy’s National Institute of Geophysics and Volcanology. (PHOTO BY ALESSANDRO LO PICCOLO)