Natural Hazards and Disasters: Volcano of the Week!

12/05/2014-18/05/2014

This week’s volcano of the week is:

Mount Vesuvius

Location: Italy

Type: Stratovolcano

Elevation: 1281 metres, 4202 feet

Last Eruption: 1944

Status: Dormant

Details:

Mount Vesuvius or Monte Vesuvio is classified as an extremely violent and dangerous volcano which is best known for its catastrophic eruption in 79 AD which resulted in the total devastation of the towns of Pompeii and Herculaneum and claimed an estimated 16,000 lives. Since the 79 AD eruption Vesuvius has killed a large number of people and erupted a number of times, of which the last one was in 1944 and the volcano is dormant at present.

Vesuvius formed in Mount Somma’s caldera, the original higher volcano which is why the volcano is also referred to as Somma-Vesuvius. It is believed that Mount Somma’s caldera started forming 17,000 years ago during an eruption. The image below shows the two volcanoes/volcanic remains and what would have been the original structure of Mount Somma.

(Source: INGV)

The volcano is part of the Campanian volcanic arc which is formed by the African plate being subducted beneath the Eurasian plate (convergent plate boundary).

The table below shows the main features of Vesuvius.

Cones
Feature Name	Feature Type	Elevation
Bocca del Viulo	Vent
Camaldoli della Torre	Cone
Fossamonaca	Vent
Gran Cono	Stratovolcano	1281 m
I Monticelli	Vent
Masseria Bosco del Monaco	Vent
Somma, Monte	Stratovolcano	1132 m
Tironi	Vent
Domes
Feature Name	Feature Type	Elevation
Colle Margherita	Dome	959 m
Colle Umberto	Dome	873 m

Source: Global Volcanism Program

Vesuvius/Somma has erupted numerous times in the past 17,000 years. The table below shows a summary of the eruption dates, details and Volcanic Explosivity Indices (VEI). The volcano is associated with both effusive and explosive eruptions resulting in pyroclastic density currents. 8 major eruptions with VEI 4 and 5 have taken place in the past, of which the famous 79 AD eruption was one.

Start Date	Stop Date	Eruption Certainty	VEI	Evidence	Activity Area or Unit
1913 Jul 5	1944 Apr 4	Confirmed	3	Historical Observations	Summit and upper flanks
1875 Dec 18	1906 Apr 22	Confirmed	4	Historical Observations	Summit and upper flanks
[ 1874 Jan ]	[ Unknown ]	Uncertain	1
1870 Dec	1872 Apr 30	Confirmed	3	Historical Observations	Summit and upper NW and south flanks
1864 Feb 10	1868 Nov 26	Confirmed	2	Historical Observations	Summit and upper SE flank
1855 Dec 19	1861 Dec 31	Confirmed	3	Historical Observations	Summit and SW flank (300-225 m)
1854 Dec 14	1855 May 27	Confirmed	3	Historical Observations	Summit and upper N flank
1841 Sep 20	1850 Feb 16	Confirmed	2	Historical Observations	Summit, upper N and E flanks
1835 Jan	1839 Jan 3	Confirmed	3	Historical Observations	Summit, upper east and west flanks
1824 Jul 2	1834 Sep 2	Confirmed	3	Historical Observations	Summit, upper E and S flanks
1796 Jan	1822 Nov 16	Confirmed	3	Historical Observations	Summit and upper flanks
1783 Aug 18	1794 Jul 5	Confirmed	3	Historical Observations	Summit and SW flank (550-300 m)
1770 Feb 15	1779 Oct 4 (?)	Confirmed	3	Historical Observations	Summit, N, NE, SE and E flanks
1764	1767 Oct 27	Confirmed	3	Historical Observations	Summit, upper SW, SE, and NNW flanks
1744 Nov (?)	1761 Jan 6	Confirmed	3	Historical Observations	Summit, upper SE, E and lower S flanks
1742	1743	Confirmed	1	Historical Observations
1732 Dec 25	1737 Jun 4	Confirmed	3	Historical Observations	Summit and SW flank
1724 Sep 4	1730 Apr 1 (?)	Confirmed	3	Historical Observations
1708 Aug 14	1723 Jul 8	Confirmed	3	Historical Observations	Summit, upper east and south flanks
1701 Jul 1	1707 Aug 22	Confirmed	3	Historical Observations	Summit and SW flank
1697 Sep 15	1698 Jul	Confirmed	3	Historical Observations
1696 Jul 31	1696 Aug 14 (?)	Confirmed	2	Historical Observations
1685 Oct 3	1694 Apr 29	Confirmed	3	Historical Observations
1682 Aug 12	1682 Aug 22	Confirmed	3	Historical Observations
1654 Feb 25	1680 Mar 28	Confirmed	3	Historical Observations
1637 Jul 1	1652 Dec	Confirmed	2	Historical Observations
1631 Dec 16	1632 Jan 31 (?)	Confirmed	5	Historical Observations	Summit, SW and S flanks
1570 (in or before)	1572 ± 1 years	Confirmed	1	Historical Observations
1500	Unknown	Confirmed	2	Historical Observations
[ 1347 ]	[ Unknown ]	Uncertain	2
[ 1270 ]	[ Unknown ]	Uncertain	2
1150	Unknown	Confirmed	3	Historical Observations
1139 Jun 1	1139 Jun 9	Confirmed	3	Historical Observations
[ 1073 ± 5 years ]	[ Unknown ]	Uncertain	3
[ 1049 ]	[ Unknown ]	Uncertain	1
1037 Jan 27	Unknown	Confirmed	3	Historical Observations	Summit and south flank (I Monticelli?)
1006 Dec 31 ± 365 days	Unknown	Confirmed	3	Historical Observations
0999	Unknown	Confirmed	3	Historical Observations	Summit and south flank (Fossamonaca)
0991	Unknown	Confirmed	3	Historical Observations
0968 Dec 1 ± 30 days	Unknown	Confirmed	4	Historical Observations
0900 ± 40 years	Unknown	Confirmed	0	Magnetism	South and west (Tironi) flanks
0860 ± 50 years	Unknown	Confirmed	0	Magnetism	South flank
0787 Oct 15 ± 45 days	0788 Jan 15 ± 45 days	Confirmed	3	Historical Observations	Summit and south flank
0685 Feb	0685 Mar	Confirmed	4	Historical Observations
0536	Unknown	Confirmed		Historical Observations
0512 Jul 8	Unknown	Confirmed	4	Historical Observations
[ 0505 Nov 9 ]	[ Unknown ]	Uncertain	2
0472 Nov 5	0472 Nov 6 (?)	Confirmed	5	Historical Observations
0379	0395	Confirmed	2	Historical Observations
[ 0303 ]	[ Unknown ]	Uncertain	2
0222	0235	Confirmed	2	Historical Observations
0203	Unknown	Confirmed	4	Historical Observations
0172	Unknown	Confirmed	3	Historical Observations
0079 Oct 24 (?)	0079 Oct 28 ± 1 days	Confirmed	5	Historical Observations
0217 BCE	0216 BCE	Confirmed	3	Historical Observations	AP6 tephra
0600 BCE (in or before)	Unknown	Confirmed	3	Anthropology
0880 BCE ± 50 years	Unknown	Confirmed	4	Radiocarbon (corrected)	AP3 tephra
1430 BCE ± 300 years	Unknown	Confirmed	4	Radiocarbon (corrected)	AP2 tephra
1550 BCE ± 75 years	Unknown	Confirmed	4	Radiocarbon (corrected)	AP1 tephra
2420 BCE ± 40 years	Unknown	Confirmed	5	Radiocarbon (corrected)
6940 BCE ± 100 years	Unknown	Confirmed	5	Radiocarbon (corrected)	Mercato Pumice

(Source: Global Volcanism Program)

79 AD eruption:

Prior to the eruption of 79 AD a large earthquake occurred in 62 AD which caused the destruction of buildings in the towns of Pompeii and Naples. Several smaller earthquakes occurred before the eruption in 79 AD, however the population did not take precautionary measures since they had become accustomed to the earthquakes.

The eruption began on the noon of 24^th August 79 AD; an explosion was followed by an ash column reaching an estimated height of up to 30 km. Tephra including pumice and hot ash fell on Pompeii at an estimated rate of 15 cm/h causing roofs to collapse and fatalities. After midnight the eruption became more violent when the ash column collapsed causing pyroclastic density currents with temperatures of over 300 degrees Celsius to travel towards the town of Herculaneum destroying and burying everything in its path. Early in the morning of 25^th August, a pyroclasic density current travelled towards Pompeii obliterating the town. The victims died of asphyxiation and were buried by ash, leaving the bodies preserved. A small tsunami is also believed to have occurred during the eruption phase. The towns of Pompeii and Herculaneum became buried under 13 to 20 feet of ash and remained buried until excavations began in 1748.

Pliny the Younger wrote detailed eye witness accounts (as shown below) of the eruption from the town of Misenum. The term Plinian eruption is named after him due to his detailed description of the eruption.

Letter 1 by Pliny the Younger (AD 61-113)

'My dear Tacitus,

You ask me to write you something about the death of my uncle so that the account you transmit to posterity is as reliable as possible. I am grateful to you, for I see that his death will be remembered forever if you treat it [sc. in your Histories]. He perished in a devastation of the loveliest of lands, in a memorable disaster shared by peoples and cities, but this will be a kind of eternal life for him. Although he wrote a great number of enduring works himself, the imperishable nature of your writings will add a great deal to his survival. Happy are they, in my opinion, to whom it is given either to do something worth writing about, or to write something worth reading; most happy, of course, those who do both. With his own books and yours, my uncle will be counted among the latter. It is therefore with great pleasure that I take up, or rather take upon myself the task you have set me.

He was at Misenum in his capacity as commander of the fleet on the 24th of August [sc. in 79 AD], when between 2 and 3 in the afternoon my mother drew his attention to a cloud of unusual size and appearance. He had had a sunbath, then a cold bath, and was reclining after dinner with his books. He called for his shoes and climbed up to where he could get the best view of the phenomenon. The cloud was rising from a mountain-at such a distance we couldn't tell which, but afterwards learned that it was Vesuvius. I can best describe its shape by likening it to a pine tree. It rose into the sky on a very long "trunk" from which spread some "branches." I imagine it had been raised by a sudden blast, which then weakened, leaving the cloud unsupported so that its own weight caused it to spread sideways. Some of the cloud was white, in other parts there were dark patches of dirt and ash. The sight of it made the scientist in my uncle determined to see it from closer at hand.

He ordered a boat made ready. He offered me the opportunity of going along, but I preferred to study-he himself happened to have set me a writing exercise. As he was leaving the house he was brought a letter from Tascius' wife Rectina, who was terrified by the looming danger. Her villa lay at the foot of Vesuvius, and there was no way out except by boat. She begged him to get her away. He changed his plans. The expedition that started out as a quest for knowledge now called for courage. He launched the quadriremes and embarked himself, a source of aid for more people than just Rectina, for that delightful shore was a populous one. He hurried to a place from which others were fleeing, and held his course directly into danger. Was he afraid? It seems not, as he kept up a continuous observation of the various movements and shapes of that evil cloud, dictating what he saw.

Ash was falling onto the ships now, darker and denser the closer they went. Now it was bits of pumice, and rocks that were blackened and burned and shattered by the fire. Now the sea is shoal; debris from the mountain blocks the shore. He paused for a moment wondering whether to turn back as the helmsman urged him. "Fortune helps the brave," he said, "Head for Pomponianus."

At Stabiae, on the other side of the bay formed by the gradually curving shore, Pomponianus had loaded up his ships even before the danger arrived, though it was visible and indeed extremely close, once it intensified. He planned to put out as soon as the contrary wind let up. That very wind carried my uncle right in, and he embraced the frightened man and gave him comfort and courage. In order to lessen the other's fear by showing his own unconcern he asked to be taken to the baths. He bathed and dined, carefree or at least appearing so (which is equally impressive). Meanwhile, broad sheets of flame were lighting up many parts of Vesuvius; their light and brightness were the more vivid for the darkness of the night. To alleviate people's fears my uncle claimed that the flames came from the deserted homes of farmers who had left in a panic with the hearth fires still alight. Then he rested, and gave every indication of actually sleeping; people who passed by his door heard his snores, which were rather resonant since he was a heavy man. The ground outside his room rose so high with the mixture of ash and stones that if he had spent any more time there escape would have been impossible. He got up and came out, restoring himself to Pomponianus and the others who had been unable to sleep. They discussed what to do, whether to remain under cover or to try the open air. The buildings were being rocked by a series of strong tremors, and appeared to have come loose from their foundations and to be sliding this way and that. Outside, however, there was danger from the rocks that were coming down, light and fire-consumed as these bits of pumice were. Weighing the relative dangers they chose the outdoors; in my uncle's case it was a rational decision, others just chose the alternative that frightened them the least.

They tied pillows on top of their heads as protection against the shower of rock. It was daylight now elsewhere in the world, but there the darkness was darker and thicker than any night. But they had torches and other lights. They decided to go down to the shore, to see from close up if anything was possible by sea. But it remained as rough and uncooperative as before. Resting in the shade of a sail he drank once or twice from the cold water he had asked for. Then came an smell of sulfur, announcing the flames, and the flames themselves, sending others into flight but reviving him. Supported by two small slaves he stood up, and immediately collapsed. As I understand it, his breathing was obstructed by the dust-laden air, and his innards, which were never strong and often blocked or upset, simply shut down. When daylight came again 2 days after he died, his body was found untouched, unharmed, in the clothing that he had had on. He looked more asleep than dead.

Meanwhile at Misenum, my mother and I-but this has nothing to do with history, and you only asked for information about his death. I'll stop here then. But I will say one more thing, namely, that I have written out everything that I did at the time and heard while memories were still fresh. You will use the important bits, for it is one thing to write a letter, another to write history, one thing to write to a friend, another to write for the public.

Farewell.

Pliny Letter 2

My dear Tacitus,

You say that the letter I wrote for you about my uncle's death made you want to know about my fearful ordeal at Misenum (this was where I broke off). "The mind shudders to remember ... but here is the tale."

After my uncle's departure I finished up my studies, as I had planned. Then I had a bath, then dinner and a short and unsatisfactory night. There had been tremors for many days previously, a common occurrence in Campania and no cause for panic. But that night the shaking grew much stronger; people thought it was an upheaval, not just a tremor. My mother burst into my room and I got up. I said she should rest, and I would rouse her (sc. if need be). We sat out on a small terrace between the house and the sea. I sent for a volume of Livy; I read and even took notes from where I had left off, as if it were a moment of free time; I hardly know whether to call it bravery, or foolhardiness (I was seventeen at the time). Up comes a friend of my uncle's, recently arrived from Spain. When he sees my mother and me sitting there, and me even reading a book, he scolds her for her calm and me for my lack of concern. But I kept on with my book.

Now the day begins, with a still hesitant and almost lazy dawn. All around us buildings are shaken. We are in the open, but it is only a small area and we are afraid, nay certain, that there will be a collapse. We decided to leave the town finally; a dazed crowd follows us, preferring our plan to their own (this is what passes for wisdom in a panic). Their numbers are so large that they slow our departure, and then sweep us along. We stopped once we had left the buildings behind us. Many strange things happened to us there, and we had much to fear.

The carts that we had ordered brought were moving in opposite directions, though the ground was perfectly flat, and they wouldn't stay in place even with their wheels blocked by stones. In addition, it seemed as though the sea was being sucked backwards, as if it were being pushed back by the shaking of the land. Certainly the shoreline moved outwards, and many
sea creatures were left on dry sand. Behind us were frightening dark clouds, rent by lightning twisted and hurled, opening to reveal huge figures of flame. These were like lightning, but bigger. At that point the Spanish friend urged us strongly: "If your brother and uncle is alive, he wants you to be safe. If he has perished, he wanted you to survive him. So why are you
reluctant to escape?" We responded that we would not look to our own safety as long as we were uncertain about his. Waiting no longer, he took himself off from the danger at a mad pace. It wasn't long thereafter that the cloud stretched down to the ground and covered the sea. It girdled Capri and made it vanish, it hid Misenum's promontory. Then my mother began to beg and urge and order me to flee however I might, saying that a young man could make it, that she, weighed down in years and body, would die happy if she escaped being the cause of my death. I replied that I wouldn't save myself without her, and then I took her hand and made her walk a little faster. She obeyed with difficulty, and blamed herself for delaying
me.

Now came the dust, though still thinly. I look back: a dense cloud looms behind us, following us like a flood poured across the land. "Let us turn aside while we can still see, lest we be knocked over in the street and crushed by the crowd of our companions." We had scarcely sat down when a darkness came that was not like a moonless or cloudy night, but more like the black of closed and unlighted rooms. You could hear women lamenting, children crying, men shouting. Some were calling for parents, others for children or spouses; they could only recognize them by their voices. Some bemoaned their own lot, other that of their near and dear. There were some so afraid of death that they prayed for death. Many raised their hands to the gods, and even more believed that there were no gods any longer and that this was one last unending night for the world. Nor were we without people who magnified real dangers with fictitious horrors. Some announced that one or another part of Misenum had collapsed or burned; lies, but they found believers. It grew lighter, though that seemed not a return of day, but a sign that the fire was approaching. The fire itself actually stopped some distance away, but darkness and ashes came again, a great weight of them. We stood up and shook the ash off again and again otherwise we would have been covered with it and crushed by the weight. I might boast that no groan escaped me in such perils, no cowardly word, but that I believed that I was perishing with the world and the world with me, which was a great consolation for death.

At last the cloud thinned out and dwindled to no more than smoke or fog. Soon there was real daylight. The sun was even shining, though with the lurid glow it has after an eclipse. The sight that met our still terrified eyes was a changed world, buried in ash like snow. We returned to Misenum and took care of our bodily needs, but spent the night dangling between
hope and fear. Fear was the stronger, for the earth was still quaking and a number of people who had gone mad were mocking the evils that had happened to them and others with terrifying prognostications. We still refused to go until we heard news of my uncle, although we had felt danger and expected more.

You will read what I have written, but will not take up your pen, as the material is not the stuff of history. You have only yourself to blame if it seems not even proper stuff for a letter.

Farewell'.

Source: GVP

Excavated stadium in Pompeii.

Source: Global Volcanism Program-Photo by Dan Dzurisin (U.S. Geological Survey), 1983

Source: National Geographic

Victims of Vesuvius Source: BBC

1631:

The 1631 eruption began on 16^th December producing a Plinian ash column which reached heights of up to 28 km. The eruption produced pyroclastic density currents, lahars, lava flows and tephra. Ash affected towns and cities to the east of the volcano and even fell as far as Constantinople (Istanbul), over 1200 kilometres (750 miles) away. Lahars and lava flows from the eruption killed over 3, 500 people.

1944:

The last eruption of Vesuvius occurred on 18^th March 1944 and lasted 2 weeks, beginning with effusive lava flows and becoming more explosive on 21^st March when eight lava fountains were produced, some which reached heights of 1000 metres. A few lava flows travelled towards towns and villages around the vicinity of the volcano including San Sebastiano and Massa di Somma causing destruction in their path.

The eruption included ash columns, lava flows and fountains, tephra including scoria and lapilli and pyroclastic density currents. The eruption ended on 29^th March 1944 leaving a 300 metres deep crater at the summit and claiming 28 lives.

Source: Global Volcanism Program-Photo by US Navy)

Evidence of lava flow from the 1944 eruption. Source: Global Volcanism Program- Photo by Roberto Scandone, 1989

Crater of Vesuvius with tephra and lava flows from the 1944 eruption. Source: Global Volcanism Program-Photo by Roberto Scandone, 1989

1999:

On 9^th October 1999 a magnitude 3.6 earthquake struck Vesuvius. It was the largest earthquake swarm since 1944 and was felt within a distance of 25 km of the volcano, making it more important to monitor the volcano closely and understand it, thus preventing false alarms in the future.

If the same magnitude eruption as the one in 79 AD takes place today, the result would be devastating and overwhelming, claiming thousands of lives and affecting millions. Today an eruption would affect over three million people, of which two million live in the immediate area around Mount Vesuvius in towns and cities such as Pompeii, Herculaneum and Naples. In some areas the population density is extremely high with 20,000 to 30,000 people per kilometres squared therefore increasing the vulnerability of the population. Over 500,000 people live dangerously close to the volcano in 18 towns which would result in them having little hope to survive since evacuation in less than 24 hours would be extremely difficult to conduct successfully. It is predicted that the most likely kinds of eruptions that will take place are strombolian, Vulcanian, Vesuvian or Plinian.

Currently there is an evacuation plan of 700,000 people around Vesuvius in a weeks warning time, in 4000 cars, 81 ships and 40 trains a day. 18 towns around the volcano would have to be evacuated. It is also stated that 16,500 people would be needed to manage this evacuation. However the questions to be raised by this are:

1. Is the plan realistic?

2. Will it really be possible to follow planned procedures whilst panic is amongst the population and authorities?

3. Where would the large number of people needed to manage the evacuation come from?

4. What about transport chaos which would prevent the evacuation to take place rapidly caused when the eruption occurs?

5. Will there not be a large amount of the population left behind due to confusion and unsuccessful evacuation?

6. What about the threats of a false alarm?

More importantly, volcanic eruptions are not always followed by precursors and many occur without even a few hours warning. It would therefore be unrealistic to plan according to the current evacuation plan which is based on a 7 day warning. In true sense volcanic eruptions cause panic and chaos, therefore carrying out evacuation measures would be more difficult and complex than simply following an evacuation plan. The Italian Government as a result is finding other means of reducing the risk of which one includes paying incentives to the residents living in the vicinity of the volcano to move out of the red zone.

Evacuation destinations (Source: David K. Chester et al)

Vesuvius is one the most studied volcano today. It is closely monitored by National Institute of Geophysics and Volcanology (INGV) in one of the oldest volcano observatory in the world (http://www.ov.ingv.it/ov/en/vesuvio.html). Numerous scientific studies which have included sophisticated GIS and statistical 2d and 3d models have been produced to predict the hazard and risk assessment of a potential eruption at Vesuvius. Below are examples of maps and models produced by a few studies. The devastation caused my a potential eruption at Vesuvius makes it essential to be understood and monitored in order to save lives in the future.