Decade Volcano: Vesuvius

This is what the least worrisome scenario for the next eruption at Mount Vesuvius looks like.

Experts who must be more specific than the rest of us call this 1944 event a “violent Strombolian eruption.”

What’s that?

Well, when we look at the picture we only see Nature’s wrath terrorizing people and ruining the neighborhood, not to mention US Air Force property.

But people whose job it is to protect residents in the area see effusion: basically, lava flows on the slopes and lava in the crater blowing huge bubbles of volcanic gas like Stromboli, off the north coast of Sicily does.

Vesuvius had its most violent Strombolian eruption in 1906, which Frank Perret observed from way too close at the Vesuvius Observatory shown in the above video. It’s now a museum, but when established in 1841, this was the world’s first volcano observatory. You don’t need to understand Italian: images speak a thousand words.

Emergency managers in and around Naples know that violent Strombolian eruptions are Number Three on the list of Vesuvian troubles.

The other two, really problematic ones are explosive eruptions.

Number One, of course, is a plinian event like the Pompeii-killer of 79 AD. Vesuvius buried other places that day — most notably, Herculaneum — but we all know Pompeii.

This was in every sense a plinian eruption:

  • The eruption column was energetic enough to shoot upward through local winds and then spread out like an umbrella at high altitudes.
  • Pliny the Elder, a soldier and the greatest naturalist of the day, died in this eruption.
  • His nephew, Pliny the Younger, wrote down what he witnessed, first from the home he shared, across the Bay of Naples from Vesuvius, with his uncle and mother, and then later on during the evacuation. His letters are the first scientific report of a volcanic eruption.

That’s two scientific “firsts” at Vesuvius now: Pliny the Younger’s reports and the Vesuvius Observatory.

What gives scientists and emergency managers nightmares is the possibility that Vesuvius might also become the first place where pyroclastic flows race into one of the world’s great cities.

They have therefore developed a National Vesuvius Emergency Plan (Italian).

It’s based on our list’s Number Two entry: a subplinian eruption like the one in 1631, which killed some 4,000 people.

Without an evacuation, those numbers today would be at least in the hundreds of thousands.

So, to review, the three worst eruption scenarios at Vesuvius (Baxter et al.) are:

  1. Plinian (Pompeii):

  2. Subplinian (1631, today’s worst-case scenario, statistically four times more likely than a plinian event):

  3. Violent Strombolian eruptions (1906 and 1944, ten times more likely than plinian activity):

A technical note: Volcanologists can’t agree on the dividing line between “plinian” and “subplinian.”

For this post I’m following the civil protection people, who need to be hardnosed about it. Their “plinian” is VEI 5, like the Pompeii eruption; their “subplinian” is VEI 4.

No ifs, ands, or buts.

Of course, this raises the question of whose word counts the most when millions of lives are at stake:

  • Scientists who have many ifs, ands, and buts when it comes to predicting eruptions, and who also know enough about Vesuvius to admit that their understanding of this complex volcano is full of gaps?
  • Civil authorities who must work within budget constraints, give clear information to the public, and need guidelines in order to draw up plans to safely move huge crowds out of harm’s way, support them during the crisis, and then help them recover?


You’re not alone in wanting to set this whole issue aside. That’s exactly what everyone did for centuries, until the Decade Volcano program led to the first-ever Vesuvius evacuation plan in 1995.

Now that’s a Vesuvian first we can all cheer!

The plan is regularly updated, last in 2018, as more scientific information becomes available.

Before looking at it, let’s get to know Vesuvius a little better.


40.821° N, 14.426° E, in Naples District, Campania Region, Italy. The GVP Volcano Number is 211020.

Nearby Population:

Per the Global Volcanism Program, not counting tourists:

  • Within 5 km (3 miles): 19,162
  • Within 10 km (6 miles): 675,705
  • Within 30 km (19 miles): 3,907,941
  • Within 100 km (62 miles): 6,009,961

Current Status:

Normal, Aviation Code Green.


  • Eruption styles: According to Michigan Tech, Vesuvius is very versatile. Instead of terrifying explosions, it sometimes exudes lava and has hosted lava fountains and lakes at times (not currently). It also has that Strombolian activity, as well as one-off Vulcanian pops like those seen at Mexico’s Popocatepetl these days as well as at this eruption type’s namesake: Vulcano, another small volcanic island off Sicily’s north coast. Vesuvius has been sitting there quietly fuming since 1944.

    Volcanologists study the geological history here with an eye to predicting what it will do next. Such a prediction is not yet possible, per Baxter et al., but many papers describe cycles of activity.

    Not everyone buys this (Scandone et al), and the details vary from study to study, but in general researchers describe a plinian blast, an “interplinian” period of lesser activity, eventual dormancy that can last for centuries, another plinian event.

    Each cycle’s details are different from those of other cycles, but that overall pattern has been recognized by some Vesuvius experts. And since the volcano has been quiet for an unusually long time (76 years), it’s possible that Vesuvius has entered a rest period that could last for more decades or even centuries. Good news for Naples, if true — a big “if.”

  • Bronze Age neighbors fleeing Vesuvius’ wrath during the Avellino eruption left behind footprints, as well as their homes and belongings.
    (Pierpaolo Petrone via Wikimedia, public domain.)

  • Biggest recorded event: Pompei in AD 79 was the last plinian eruption in historic times. The VEI 5 before that — the Avellino Pumice eruption — was even worse. It happened almost four thousand years ago. The Bronze Age people it evicted left their footprints, and on at least one occasion, their remains in the ash. Some of those footprints, per Mastrolorenzo et al., are just a few miles from metropolitan Naples. And the Avellino pyroclastic surge bed in Naples is almost 10 feet deep.
  • Most recent eruption: 1944.
  • Past history: See the GVP for details. It’s a long list.


The Vesuvius Observatory, National Institute of Geophysics and Volcanology (INGV).

INGV seismic monitoring

Toulouse VAAC (Volcanic Ash Advisory Center).

Some webcams and satellite data

National Vesuvius Emergency Plan

First off, this is a work in progress and always has been. It’s designed that way so the latest information can be included.

Secondly, this is the national plan. There also should be plans in place by local authorites to implement it.

Basically, it’s hazard based:

Civil Protection (PDF downloaf)

  1. Red Zone: This area is particularly vulnerable to pyroclastic flows. Intense tephra (ash and other debris) fall is also a threat. Immediate evacuation is the only way to protect the hundreds of thousands of people who live here. Ideally, this should happen before the eruption starts; if not then, people need to get out before the main phase gets going.

    There is some discrepancy in online sources. These may be quoting old information when mentioning a warning time of two weeks. That’s how long precursors to the 1631 reference eruption lasted, but today’s Civil Protection plans call for a 72-hour window.

    Of course, the devil is in the details, which are too complex to go into here. They are thoroughly discussed in sources listed below.

  2. Yellow Zone: Roof and building collapse from tephra is the main threat here, based on how things played out in 1631. More time is available here to determine where the most ash will fall, given current weather conditions. Those are the areas that will need evacuation at some point after the eruption starts.
  3. Blue zone: Blue is for water. Flooding isn’t a hazard we normally associate with eruptions, unless there’s a crater lake involved or lava blocks a waterway. Some eyewitness reports, however, describe something like a river coming from the flanks of Vesuvius during an eruption, and geologists have found evidence of floods. Lahars (mudflows) are a threat, too. These areas are now in the Blue Zone.

Evacuations in the Yellow and Blue zones only differ in timing from those in the Red Zone. They will be called after the eruption has begun and authorities know which areas are most at risk.

This is a luxury those in the Red Zone can’t afford. Pyroclastic flows move too quickly for anyone to think about lingering there.

Each municipality in harm’s way is “twinned” with a similar region in a safer part of Campania that will host evacuees until they can go back home or make other arrangements. Final accords were signed for this last year.

If you want to learn more, ArcGIS has a nice online story map map to get you started.

This reviews past and present plans, with lots of pictures as well as maps, and also proposes a scientific alternative, weighing its pros and cons.

From there, check out some of the sources listed below.

You will quickly discover just how complex and challenging it is to come up with a good solution for the human hazards Vesuvius poses.

But there is a plan now.

And that in itself is a great success.

I don’t know what they are saying about the plan in this 2016 video, but it’s a good place to mention a uniquely Italian approach I read about. Just before they call a full Red Zone evacuation, they are going to empty hospitals and care centers — and place protection around monuments and other heritage!

Featured image: San Diego Air and Space Museum, public domain.


Avvisati, G.; Sessa, E. B.; Colucci, O.; Marfè, B.; and others. 2019. Perception of risk for natural hazards in Campania Region (Southern Italy). International Journal of Disaster Risk Reduction, 40: 101164.

Baxter, P. J.; Aspinall, W. P.; Neri, A.; Zuccaro, G.; and others. 2008. Emergency planning and mitigation at Vesuvius: A new evidence-based approach. Journal of volcanology and geothermal research, 178(3): 454-473.

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.

Civil Protection. 2018. The updated National Vesuvius Plan. Last accessed July 18, 2020.

Edwards, C. 2016. Italy puzzles over how to save 700,000 people from the wrath of Vesuvius. Last accessed July 17, 2020.

Mastrolorenzo, G.; Petrone, P.; Pappalardo, L.; and Sheridan, M. F. 2006. The Avellino 3780-yr-BP catastrophe as a worst-case scenario for a future eruption at Vesuvius. Proceedings of the National Academy of Sciences, 103(12): 4366-4370.

Mei, E. T. W.; Lavigne, F.; Picquout, A.; De Bélizal, E.; and others. 2013. Lessons learned from the 2010 evacuations at Merapi volcano. Journal of Volcanology and Geothermal Research, 261: 348-365.

Michigan Tech. 1996. Vesuvio.

Newhall, C. 1996. IAVCEI/International Council of Scientific Union’s Decade Volcano projects: Reducing volcanic disaster. status report. US Geological Survey, Washington, DC. Retrieved from

Oregon State University: Volcano World. 2020. What’s the most recent eruption of Vesuvius and will it erupt again?’s-most-recent-eruption-vesuvius-and-will-it-erupt-again Last accessed July 18, 2020.

Scandone, R.; Giacomelli, L.; and Speranza, F. F. 2006. The volcanological history of the volcanoes of Naples: a review. Developments in Volcanology, 9: 1-26.

Solana, M. C.; Kilburn, C. R.; and Rolandi, G. 2008. Communicating eruption and hazard forecasts on Vesuvius, Southern Italy. Journal of Volcanology and Geothermal Research, 172(3-4): 308-314.

De Vivo, B.; Petrosino, P.; Lima, A.; Rolandi, G.; and Belkin, H. E. 2010. Research progress in volcanology in the Neapolitan area, southern Italy: a review and some alternative views. Mineralogy and Petrology, 99(1-2): 1-28.

Wikipedia (Italian). 2020. Vesuvio. Last accessed July 17, 2020.

Wilson, G.; Wilson, T. M.; Deligne, N. I.; and Cole, J. W. 2014. Volcanic hazard impacts to critical infrastructure: A review. Journal of Volcanology and Geothermal Research, 286: 148-182.

Zuccaro, G., and De Gregorio, D. 2019. Impact assessments in volcanic areas — The Vesuvius and Campi Flegrei cases studies. Annals of Geophysics, 62(1): 02.

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