Decade Volcano: Etna


From a distance, Sicily’s Mount Etna looks like your basic stratovolcano: large and pointy-topped with lots of lava flows on its slopes.

Extra points for looming dramatically over a city (Catania, in the above image)!

But looks can be deceiving, especially on such an active fire mountain.

Etna did have a summit cone in the early 20th century. Then activity changed and today there are four summit craters.

More than one of these can erupt at any given moment:



Most of the action in this 2013 video is at the New Southeast Crater. That second blast is from Etna’s Northeast Crater (opened in 1911). New Southeast Crater (2007) is actually part of the Southeast Crater (1971). Etna’s other two summit vents, not seen here, are Voragine (1945) and Bocca Nuova (1968).


Etna erupts from fissures in its flanks, too. This happens less often than at the summit, but it also occurs at lower altitudes — closer to human settlements.

Lava from flank eruptions has wiped out villages and farmlands more than once. In 1669, it even damaged part of Catania, 11 miles away!

Local residents tried unsuccessfully to divert the lava in 1669, but later attempts have worked better, including one in 1983, one during the International Decade, and one in 2001.

John Menard, CC BY-SA 2.0

Here’s another odd thing about Etna — it’s a little round-shouldered, like Mauna Loa, a shield volcano.

That’s because, technically, Mount Etna is a 1200-foot-high stratovolcano sitting on a roughly 9500-foot-tall, 36 x 24-mile-wide shield volcano. (Oregon State University)

However, in practical terms, there is no simple way to classify Etna. Fire mountains have taken many shapes here down through time, as we will see in the history section.

Around 15,000 years ago, a series of Plinian eruptions collapsed the summit into a deep caldera that many intense eruptions have since filled in, building the stratovolcano.

How do they know this?

Fortunately for volcanologists, part of the volcano’s east flank has collapsed into the sea, forming the Bove Valley.

Part of Bove Valley. (Image: Ji-Elle via Wikimedia, CC BY-SA 3.0)

Luckily for the rest of us, this happened some 10,000 years ago.

Sicily and tsunami-prone Mediterranean shores were much less densely populated then, although this still must have been a regional catastrophe.

Today, expert eyes can read many details of Etna’s complex history in the exposed inner layers that form the walls of Bove Valley.

It also helps that Etna has the longest documented eruption history of any volcano, going all the way back to 1500 BC. (Oregon State University)

Its valuable archive of volcanic processes and physical accessibility made Mount Etna, like Mauna Loa, an obvious candidate for the Decade Volcano program.

Just one of the many monitoring instruments on Etna. (Image: Leandro Neumann Ciuffo, CC BY- 2.0)

But ongoing intense activity here also puts more than a million Sicilians in harm’s way.

As well, Etna’s emissions interfere with air traffic and occasionally have scattered ash and noxious gases as far away as Greece and Libya.

Today, Etna is one of the most heavily monitored volcanoes in the world. That’s especially good news in light of recent studies showing that its eruptions have been getting more frequent and more productive since the 1970s. (DelNegro et al.; Etna Observatory)

Location:

37.748° N, 14.999° E, Sicily. The GVP Volcano Number is 211060.

Nearby Population:

Per the Global Volcanism Program website:

  • Within 5 km (3 miles): 78
  • Within 10 km (6 miles): 3,291
  • Within 30 km (19 miles): 1,016,540
  • Within 100 km (62 miles): 3,052,770

Current Status:

As of the time of writing, Aviation Code Orange or Red, depending on activity level.

Eruptions:

  • Eruption styles: Lava flows are the main hazard to people near Mount Etna (DelNegro et al.), though explosions like this near tourist areas occasionally injure nearby visitors; sometimes property damage from summit eruptions is severe enough to affect the local tourist economy. Etna also has frequent lava fountaining and Strombolian-style explosions that are gorgeous but can cause damaging local and long-distance ashfall.
  • Biggest recorded event: A Plinian eruption in 122 BC damaged Catania so badly that Rome’s Senate gave the city ten tax-free years.

    However, many experts regard the 1669 AD event as Etna’s most destructive eruption in recorded times.

    Wikimedia

    About one cubic kilometer of lava poured out of the volcano’s flank.

    It traveled through an extensive complex of lava tubes (which kept it hot and flowing) all the way to the sea.

    At least nine villages were covered, and so were fields and vinyards. Besides messing up a medieval castle and adding almost a kilometer to the shoreline here, lava also overtopped Catania’s wall, damaging some neighborhoods in the western part of the city.

    There is some disagreement on casualties. Brown et al. only list 86 deaths from Etna eruptions between 1536 and 1987. However, this source states there were 20,000 fatalities in 1669 — since it’s NASA, I’m including it here but wonder about their sources.

  • Most recent eruption: Ongoing at Voragine, New Southeast, and Northeast craters.
  • Past history: See the GVP for details.

    Here it is in pictures, unless you speak Italian.



    Basically, per the Etna Observatory, volcanism first began on the Mediterranean seafloor some 500,000 years ago, in the middle Pleistocene.

    The first shield volcano may have formed through fissure eruptions between 220,000 and 110,000 years ago. Activity then centered in and around what’s now the Bove Valley 110,000 years ago and eventually moved northwest to the part that’s active today.

    We’ve already mentioned the caldera-forming explosions 15,000 years ago and the flank collapse 10,000 years ago. Keep watching and you will see the smaller caldera-forming eruption in 122 BC — ashfall from this caused roof collapses in Catania and ruined the local agricultural economy.

    This ArcGIS story has more detailed technical information about Mount Etna’s geologic history and hazards.

    Monitoring:

    The National Institute of Geophysics and Volcanology (INGV) and its Etna Observatory.


    Featured image: Antonio Lacullo via Wikimedia, CC BY-SA 3.0.


    Sources:

    Barberi, F., and Carapezza, M. L. 2004. The control of lava flows at Mt. Etna. (Abstract only) Washington DC American Geophysical Union Geophysical Monograph Series, 143: 357-369.

    Branca, S., and Del Carlo, P. 2005. Types of eruptions of Etna volcano AD 1670–2003: implications for short-term eruptive behaviour. Bulletin of Volcanology, 67(8): 732-742.

    Brown, S.K.; Jenkins, S.F.; Sparks, R.S.J.; Odbert, H.; and Auker, M. R. 2017. Volcanic fatalities database: analysis of volcanic threat with distance and victim classification. Journal of Applied Volcanology, 6: 15.

    DelNegro, C.; Cappello, A.; Neri, M.; Bilotta, G.; and others. 2013. Lava flow hazards at Mount Etna: constraints imposed by eruptive history and numerical simulations. Scientific Reports, 3: 3493.

    Etna Observatory. 2020. Mount Etna. http://www.ct.ingv.it/index.php/ricerca/i-vulcani-siciliani/etna (via Google Translate). Last accessed April 18, 2020.

    Global Volcanism Program. 2020. Etna. https://volcano.si.edu/volcano.cfm?vn=211060&vtab=GeneralInfo. Last accessed April 18, 2020.

    Lester, L. 2020. Et tu, Etna? https://eos.org/articles/podcast-et-tu-etna. Last accessed April 19, 2020.

    Newhall, C. 1996. IAVCEI/International Council of Scientific Unions Decade Volcano projects: Reducing volcanic disaster. status report. US Geological Survey, Washington, DC. Retrieved from https://web.archive.org/web/20041115133227/http://www.iavcei.org/decade.htm

    Oppenheimer, C. 2011. Eruptions That Shook the World. Cambridge: Cambridge University Press. Retrieved from https://play.google.com/store/books/details?id=qW1UNwhuhnUC

    Oregon State University: Volcano World. 2020. Etna. http://volcano.oregonstate.edu/etna Last accessed April 18, 2020.

    Sable, J.; Houghton, B.; del Carlo, P.; and Coltelli, M. (2001, December). Mechanisms for Basaltic Plinian Volcanism: A Quantitative Study of the Products of the 122BC Eruption of Mount Etna. In AGU Fall Meeting Abstracts.

    Stenmark, J. 2020. GNSS and precise positioning to help understand movement in volcanoes. https://www.geospatialworld.net/blogs/a-major-eruption/amp/ Last accessed April 18, 2020.

    Wikipedia. 2020. Aeolian Islands. https://en.wikipedia.org/wiki/Aeolian_Islands Last accessed April 18, 2020.

    Wikipedia (Italian, via Google Translate): 2020. Catania https://it.wikipedia.org/wiki/Catania Last accessed April 18, 2020.

    ___. 2020. Etna. https://it.wikipedia.org/wiki/Etna

    ___. 2020. Linear system of eastern Siciliy. https://it.wikipedia.org/wiki/Sistema_lineare_della_Sicilia_orientale



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