Even at the most extreme edges of the flow of stuff out of the volcano Pompeii, at the far edge of the mud and ash that came from the volcano’s explosion, the heat was sufficient to instantly kill everyone, even those inside their homes.

ResearchBlogging.orgAnd that is how the people at Pompeii, who’s remains were found trapped and partly preserved within ghostly body-shaped tombs within that pyroclastic flow, died. They did not suffocate. They did not get blown apart by force. They did not die of gas poisoning. They simply cooked. Instantly.

That is the conclusion of a study just published in PLoS ONE by Giuseppe Mastrolorenzo, Pierpaolo Petrone, Lucia Pappalardo and Fabio Guarino, entitled Lethal Thermal Impact at Periphery of Pyroclastic Surges: Evidences at Pompeii.

This research was carried out specifically to address the question of survivability of certain kinds of volcanic eruptions. When this type of volcano explodes, a mixture of hot gas and fine ash flow at very high speed outwards and down slope, causing widespread devastation. It is generally assumed that people would not survive within the pyroclastic flow zone, but the question remained open as to whether people would survive at the outermost edge, where they may not be impacted directly by the flow itself.

… the evaluation of PDCs (pyroclastic flow) effects near the flow termination is widely debated being crucial for risk mitigation management, particularly for distal areas often densely inhabited. Nevertheless, these aspects are documented only in a few modern eruptions and difficult to retrieve from historical record, due to scarce availability of data on thin distal layers.

And thus, Pompeii becomes an important data point. At Pompeii, the remains of hundreds of individuals were found in the pyroclastic deposits from the famous 79 AD eruption, the one documented by Pliny the Younger and memorialized in countless books, a few movies, and a museum exhibit or two.

Yeah, like this:

(Verily, one of Ernest Borgnine’s greatest films!)

The study modeled the physics of the eruption, tying a model to the ground with the physical and archaeological data. For context:

The 79 AD Vesuvius eruption generated a sequence of six distinctive pyroclastic surges (S1 to S6) and flows with increasing power, which caused landscape modification as well widespread building collapse and fatalities [3]. The resulting ash deposits have thicknesses ranging from tens of metres near the vent to few millimetres at the flow periphery. In particular, the early three surges (S1 to S3) stopped ahead the northwestern walls of Pompeii, while the later ones (S4 to S6) over passed the town. The last two surges traveled up to a distance even exceeding 15 kilometres from the vent, whereas the S4 surge deposit least traces are confined within a few hundred of metres next to the south and southeastern walls.

The S4 surge, which deposited only a small blanketing of ash at the site, probably caused most of the fatalities in Pompeii. The 3 cm or so thick layer of ash was “emplaced suddenly in a single depositional event resulting from dusty gas mixture deflation in response to horizontal velocity and turbulence dumping at the flow termination.”

In other words, it was like “phooofff” and everybody was dead and this dusting of ash was everywhere. And I don’t really mean to be flip about this … it is hard to imagine what is being described by this analysis in real terms.

Consider this: Imagine an area about 10 kilometers (just over 6 miles) around the volcano. Now imagine that area being covered with a blanket of very hot ashy air over the course of about 3 minutes. To help imagine this, pretend you are looking at the volcano when the explosion starts, and there is an airliner over the volcano heading for you at the same time. It is moving at top speed for such an aircraft, and when it reached you it has slowed to just over 100 mph. That represents the leading edge of the blanket of hot air and ash. Just at that moment, the blanket of air and ash deflates/dissipates, the air cooling and the ash settling. But first, all humans, probably all tetrapods (birds, mammals, etc) within that few miles of space have simply dropped dead. Since there is only a little ash, they are dirtied by it, but later, a larger deposit of ash is spewed out, and now all the dead are deeply buried. Or at least, that’s what I’m getting from this paper, more or less.

… most of the victims are typically frozen in suspended actions (73% life-like stance, 27% sleep-like stance), showing as well as limb contraction (76%) and a large number of corpses presenting the pugilistic attitude (64%).

That “pugilistic attitude” bit is the appearance that the victim was fighting for his or life, but which actually occurs as a side effect of being cooked very quickly (or drying out more slowly in some cases). Everyone was killed and their bodies frozen in the position they were in at that time of instant death, plus a small bit of involuntary perimortem spasm. They were not suffocated, they were not killed by being blasted with an explosive force that knocked them down. They were cooked in situ.

Finally, contrary to previous hypotheses, our findings based on the interdisciplinary volcanological and bio-anthropological study of the deposits and victims of the 79 AD Plinian eruption reveal that even at the extreme periphery of the S4 surge neither asphyxia nor impact force but heat caused the deaths. Actually, while impact force and exposure time to dusty gas dropped below lethal conditions, the pyroclastic cloud retained its high temperature thus being the main cause of instantaneous mortality for the Vesuvius area inhabitants, including people who were sheltered within buildings as far as in Pompeii.

The temperature was 250 to 300 degrees C, and the time of exposure was about 30 seconds or so. Death would have been during the first few seconds of that time. That temperature is enough to light gasoline and other fuels under certain conditions, but not enough to ignite clothing.

So, now you know how they died.

Mastrolorenzo, G., Petrone, P., Pappalardo, L., & Guarino, F. (2010). Lethal Thermal Impact at Periphery of Pyroclastic Surges: Evidences at Pompeii PLoS ONE, 5 (6) DOI: 10.1371/journal.pone.0011127

Comments

  1. #1 Dan J
    June 27, 2010

    Damn, that’s scary. Residing on this planet is dangerous, it seems, no matter which spot you choose to settle on.

  2. #2 Art
    June 27, 2010

    I wonder if there could be an oven set up to simulate the effect of such flash-cooking. The experimental subject would be chicken or pig, all humanely dead beforehand.

    I figure an oven to heat the air mass then the air mass is driven into a semi enclosed area at suitable velocity, we could try it both with and w/o ash added during transit. It would be an interesting study.

    As far as a practical way of cooking I speculate that such flash cooking will seal in the juices and form a savory crust. You might want to substitute a nice salt and spice rub for the ash. The risk would be that the interior remains uncooked.

    The key would be controlling the duration/dissipation of the heat to get complete cooking. Varying the degree of enclosure and amount of thermal mass should allow a good bit of control. But, as always, getting it deliciously right will be something of an art.

    Once the process is perfected the “Vesuvius Cooker” can be trotted out for geology/vulcanology meetings to prepare the main course at the luncheon.

    After every experiment we have a BBQ where we eat out experimental subjects.

  3. #3 Greg Laden
    June 27, 2010

    Yes, Art, you are a truly demented person. I quickly add that I had the same exact thoughts. I my pick up some ribs at Costco later today. I’m thinking a charcoal fire, some bellows, and a leaf blower….

  4. #4 sailor
    June 27, 2010

    Mt Pelee in Martinique did much the same thing in 1902 and incinerated the town plus about 30,000 people. Dangerous thing pyroclastic flows.

  5. #5 Greg Laden
    June 27, 2010

    That is a good example. I get the impression that for Pompeii S4, there was less of a heavy duty shockwave/blast (which in the case of Pelee was strong enough to knock a steam ship off its keel) and possibly hotter air. Similarly to Pompeii, S4, there was not a huge dumping of ash on the city. Of course, each of these events is going to be different.

  6. #6 sailor
    June 28, 2010

    It is a minor point but I don’t know where you got the information a steamship was knocked of its keel. There were quite a few ships in the bay, most caught fire and sunk, and today are popular dive sites. One managed to make steam and escape, the captain steering with what was left of his burnt arms. However, the suffering a pain on board was so extreme, he considered those who perished immediately were luckier.

  7. #7 NoAstronomer
    June 28, 2010

    “landscape modification”

    One of my favorite technical terms. On a par with “Controlled flight in terrain”.

  8. #8 Sam N
    June 28, 2010

    I for one question the use of this flash cooking. It’s one thing to kill an animal, but it’s another to cook to taste. How much difference is there really between throwing that bird in the deep fryer and moving a massive amount of heated air into its vicinity? I figure in either case, it should kill the animal in seconds (I should hope…) But it still takes tens of minutes to finish cooking.

  9. #9 Anne H
    June 28, 2010

    Sam N, I thought of turkey deep-fryers as well. It’s the closest commonplace comparison I can conceive. A turkey fryer holds an enormous amount of stored heat, that is rapidly released when the turkey is immersed for cooking.

    The citizens of Pompeii were immersed in very hot gasses instead of liquid oil, but my guess (and I am a layperson and not an expert of any kind)is the results would be similar.

  10. #10 Greg Laden
    June 28, 2010

    Sailor, I read it somewhere. It could be wrong. Maybe the Internet knows.

    Ah, here it is:

    “The hurricane force of the blast capsized the steamship Grappler,”

    http://www.geology.sdsu.edu/how_volcanoes_work/Pelee.html

    Wikipedia does not say it, but that does not mean it didn’t happen.

  11. #11 sailor
    June 28, 2010

    Oh yes, capsized, that happened. I guess I guess I would not describe that as “knocking a boat off its keel,” that to me conjures up images of the boat and keel separating, which would be quite a blast! No problem

  12. #12 VolcanoMan
    June 28, 2010

    Actually, Pelee had a much higher eruption temperature than Pompeii (there have been studies done…I forget the exact value, but it was at least 600 C); also, most people there had been cooked before the pyroclastic flow could reach them. They were actually killed by the pyroclastic surge of hot gas and minimal ash that expanded outward from the pyroclastic flow (pyroclastic flows move primarily as gravity currents, so this differentiation is easy to understand – the hot air expanding faster than the acceleration of gravity the ash and rocks experience). From this study, it sounds like they concluded that a surge caused the mass death at Pompeii as well (3 cm of ash is nothing for a pyroclastic flow and the fact that even people outside S4’s ash depositing area died)…not a surprising conclusion in my opinion.

    On another note, did the paper happen to mention…how instantly? I mean, death is basically 100% certain in these things, but it is surprising (and heartening, since I am hoping my volcanic career is ended by one of these things, and I don’t want to suffer – I’m a wuss) to hear that it’d be instant. What evidence do they have that it doesn’t take more than 1 second to lose consciousness from time of exposure (my arbitrary “instant” definition).

  13. #13 Greg Laden
    June 28, 2010

    Right. Knocked off of it’s keel as in knocked off of it’s feet. But with a keel.

  14. #14 sailor
    June 28, 2010

    Greg, I will have to add that to my nautical terms…

    Volcano Man, In St. Pierre a lot of people who died suffered. This was observed by the few boat survivors, where many of them died of horrible burns, their skin peeling right off and limbs burnt like charcoal. Also they reported a few people moving around piteously after the blast in town. Strangely one one guy called Leandre survived pretty much in the center of town. His house was against a steep hill, so there may have been some protection there. Other people in his house died. He was burnt but not in a life threatening way. Must have been a small pocket of luck.
    But by and large I would not say it was likely to be completely painless. On the other hand, once dead there are no memories.

  15. #15 Ender
    June 29, 2010

    Mmm, deep fried experimental results… I could go for that.

  16. #16 R.G. Frano, A-EMT-4-P, (Ret.)
    June 29, 2010

    As a former paramedic, (with extensive experience in burn trauma),to consider the ‘experience’ of being killed in a volcano’s pyroclastic flow, reminds me of the image of a seane in the movie, “Terminator-2′, where the heroine is screaming for people to “wake up”, in a small park – just as a ‘MIRV’ hits.
    The children & guardians in the park are converted to ash & blow away, (which is probably accurate as far as a nuclear blasts go with the high winds), but the ‘quick fry’, (not to be confused with the dramatic spectacle of the screaming, burning skeleton, blown off the chain link fence), is, give or take a few milliseconds, just about right, IMHO.

  17. #17 Katrina
    June 29, 2010

    Interesting this. I remember reading that there was no doubt that the victims at Herculaneum died from pyroclastic flow. They didn’t have the ash fall that Pompeii did. I have seen the ash layers at Oplontis, which wasn’t that far from Herculaneum, but I assume (without running to get my books) that the ash fall was after that fated day in August.

  18. #18 VolcanoMan
    June 30, 2010

    Yeah, I figured that there would be at least a few seconds to a minute of consciousness. Death would technically be suffocation-based, not because of ash, but because breathing would be hindered by the lack of lung function. I don’t think insta-bake would be subjectively short either…that few seconds could feel like a few minutes.

  19. #19 Greg Laden
    June 30, 2010

    Volcano man, I’m not so sure. What is the thermal conductivity of the tissues surrounding the brain? Going from “room temperature” to 240C would probably shut the brain down long before the CP system died, although the lungs would become rather useless in a few seconds.

    That temperature is hotter than anyone ever sets their kitchen oven to.

  20. #20 Handles
    June 30, 2010

    The Indian oven known as the Tandoor can apparently be heated to 480°C.

    http://en.wikipedia.org/wiki/Tandoor

    When I make tandoori chicken in my gas oven at home, I set the dial as high as it will go (past 250°C). It takes minimum 20 minutes to cook a chicken drumstick to the bone, by which time the outside is starting to blacken slightly.

  21. #21 VolcanoMan
    June 30, 2010

    Excellent question…I have no idea. But I would think that even while the outside of your brain’s a-cookin’, the parts that keep you alive and awake are protected enough to give you some time to suffer. Unless, of course, your blood temperature goes up fast enough while the blood vessels remain intact to inundate your brain with hot blood which could cook it faster than it would cook from the outside-in.

  22. #22 Greg Laden
    June 30, 2010

    RG Franco, that is the image I had as I was writing this post. I almost mentioned the movie, but chose not to (for no particular reason).

    Handles: It takes minimum 20 minutes to cook a chicken drumstick to the bone, by which time the outside is starting to blacken slightly.

    OK but when does the clucking stop?

    Unless, of course, your blood temperature goes up fast enough while the blood vessels remain intact to inundate your brain with hot blood which could cook it faster than it would cook from the outside-in.

    Good point. I suspect it would be a race between three or four different things. The lungs would not be able to exchange O2 from the start. THe skin surface would be literally searing and boiling, which would cause instant shock, unconsiousness, etc. The neural system would freak out but the heart would keep beating, potentially, for even longer than the brain would keep operating. The brain would begin to cook pretty quickly.

    What is the effect of a zillion capillaries carrying bits of charred dermis back towards the core in the last spasmodic theree or four beats of the heart?

    I have seen live animals tossed on a camp fire numerous times. Although a wood fire can get very hot in parts, the upper parts are probably comparable to the temperatures discussed here or a bit hotter. They die quickly, but it is hard to say what from (and these have been mainly birds and small rodents being cooked by Efe foragers …. tough I once saw a snake throw itself into hot ashes and die pretty quickly).

  23. #23 Anton Mates
    June 30, 2010

    VolcanoMan,

    What evidence do they have that it doesn’t take more than 1 second to lose consciousness from time of exposure (my arbitrary “instant” definition).

    Looks like a couple of things. First, they cite a couple of other papers on eruption effects(to which I don’t have online access) which say the same thing: death from exposure to that kind of heat is pretty much instantaneous.

    Second, they have direct evidence from the life-like postures of the Pompeii victims. They say that these postures are diagnostic of full-body “cadaveric spasm”–a condition resembling superfast rigor mortis, in which the person simply stiffens in place and falls over. This is usually associated with instantaneous violent death; here they give a couple more citations and allude to observations during modern wartime.

    The authors argue that victims of suffocation generally go through a death agony, then lose muscle tone completely and lie limp until rigor mortis sets in. The Pompeii victims’ postures aren’t consistent with burial during any of those phases, so they probably weren’t suffocated; they were cooked on their feet and were dead and stiff before they hit the ground.

    Now, I think there might be a problem in their analysis–unless I’m misreading it, they don’t consider whether the insta-rigor could be a direct result of the heat and not a symptom of cadaveric spasm. Apparently mammalian muscle experiences heat rigor at 50 °C, so it seems quite possible to me that the victims’ muscles simply locked up from that effect.

    OTOH, that wouldn’t really change their conclusion. A brain temperature of 50 °C is more than enough to shut down consciousness with a vengeance, so if their muscles were instantly frozen from the heat, their minds were extinguished just as fast.

    But I would think that even while the outside of your brain’s a-cookin’, the parts that keep you alive and awake are protected enough to give you some time to suffer.

    I doubt it–not when your outside is cooking at this heat. The authors provide evidence that the victims’ skeletons reached 250-300 °C during the 30-second time of exposure; at that rate of temperature change, their brains would easily have heated to unconsciousness within a second or two.

    Also, there’s not that much to suffer from here; the nerve endings in your skin would have been converted into steam before they even had a chance to fire. The worst burns are often initially quite painless, as I understand it, and these people didn’t live past that phase.

    By the way, the authors also mention that the Herculaneum victims probably experienced internal temperatures of at least 500 °C. This instantly boiled their soft tissues off their bones–which is why most of them were skeletons at best before ash started to bury them–and in many cases their skulls actually blew open from steam pressure.

    Greg,

    That temperature is hotter than anyone ever sets their kitchen oven to.

    And there would be much quicker heat transfer than in a typical oven, I think, because of the speed of the surge gases. It’s the opposite of wind chill, the same principle as is used in a a greaseless fryer or commercial convection oven–except that the airspeed is even higher in this case.

  24. #24 bjvl
    July 5, 2010

    The one image that comes to mind, that I really must ask about, is the twisted, writhing form of the chained dog they found.

    How does that (apparent) anomaly fit with this theorum?

  25. #25 Greg Laden
    July 5, 2010

    I think the idea is that this twisting writhing stuff is what happens when your muscles are reacting to the heat while dead.

  26. #26 Sandgroper
    July 20, 2010

    Coincidentally, a few weeks ago I had the opportunity to visit a mmuseum exhibition on Pompeii, which included some body casts. I’m trying to reconcile what I saw with what is in this paper.

    The casts I saw were a small sample, and it was obviously not a random sample – they were chosen selectively, I assume at least to omit casts that might be more confronting to a general public audience. Perhaps also they were chosen on the basis of the detail which was preserved, but I’m guessing.

    The detail observable in the casts was quite remarkable – including pretty fine detail of the clothes people were wearing, body shape, etc. So these people and their clothing did not burn much if at all before they were covered by a thick layer of very fine ash in one of the phases subsequent to S4.

    In a humane sense, I found the casts to be very touching – they were very lifelike and sympathy-inducing, at least to me. In a couple of groups, people were reaching out to one another – notably one couple who were assumed to be a husband and wife, and a separate couple who were two young women. Some had their hands or the hems of their clothing held over their lower faces in a self-protective gesture.

    I have seen plenty of photos before, but seeing the casts up very close in 3D gave me a different perspective. Of those that I saw, I had the overwhelming sense that these people knew what was happening to them and were reacting to it. In other words, death was not literally instantaneous – they had time to react. It was not death by suffocation, but likewise it was not literally instantaneous. I saw no evidence of writhing or twisting that I could discern, with the exception of the guard dog, the image of which is pretty famous.

    But it was a small sample, chosen with some bias, so I should not infer too much of a general nature. And I’m no biologist. But I am somewhat familiar with deaths in natural disasters.

    But a cast of a young woman lying partly propped on one arm with the hem of her dress held up over her nose and mouth seems like pretty clear evidence she did not die instantaneously. Likewise the case of two young women lying huddled together, with one reaching out to the other, and the other case of the man and woman lying huddled together reaching out to one another.

    The authors seem to be saying a few seconds to a few tens of seconds, which seems about right to me.

  27. #27 Sandgroper
    July 20, 2010

    Addendum – from searching for images of casts, some people do look like they literally dropped dead on the spot. Others look like they died very quickly, but not instantaneously, as in this case.

    (warning – some people might find this image a bit distressing):

    http://freestockphotos.com/POMPEII/BodyCasts1.jpg

    I’m trying to find images of some of the casts I saw in the exhibition, but no luck so far.

  28. #28 Greg Laden
    July 20, 2010

    I think the idea of an almost instant death from a wave of heat is not incompatible with people knowing something was happening. It is not necessarily the case that the heat blast would have been the first thing they could have known about coming at them. (I’m guessing here)

    Anyway, you’ve made some interesting observations, but I would suggest that in any exhibit the chosen casts may be highly selected to illustrate certain points, and an exhibit designed with one process of death in mind may well be served by a different set of casts than a different exhibit with different ideas in mind.

  29. #29 Sandgroper
    July 20, 2010

    Greg, thanks. Yes, I agree on both counts.

    Finally, I found these photos of a cast of a young woman shielding her face. She was one of the casts in the exhibition:

    http://3.bp.blogspot.com/_khSBbOGByJ4/SLMzUEZNUuI/AAAAAAAAAhU/Z5WrXYBrUJQ/s400/IMG_3754.JPG

    http://spqr360.com/images/article_images/body_casts_in_pompeii.jpg

    http://www.signonsandiego.com/uniontrib/20080214/images/met-pompeii220.jpg

    http://0.tqn.com/d/ancienthistory/1/0/h/W/2/woman_800.jpg

    I previously discussed with Martin Runqvist whether it is normal to be able to feel such empathy for the suffering of a total stranger who died on the opposite side of the world nearly 2,000 years ago (yes, I appreciate the irony of that comment), and he persuaded me that I’m not going mad. Well, maybe we both are – he mentioned he sometimes talks to skulls.

  30. #30 Sandgroper
    July 20, 2010

    On your second point, I should have added that the exhibition noted that the majority of people died due to the S4 event, but they attributed it to a surge of toxic gases mixed with ash. Clearly they had not seen the evidence from the paper you linked to that it was heat rather than toxicity that was so immediately fatal.

    Sorry, I think I’m done now. It’s a subject of endless fascination.

  31. #31 Phil Jones
    France
    March 29, 2013

    The accounts of Pompeii have always intrigued me. So many people in almost normal positions, preserved.

    Ive seen various figures for the temperature and this article puts the temperature much lower at 250 while others at over 1000 degrees. Either way, a tad too hot for comfort.

    Traveling at around the speed of sound you wont hear it though you might see it….but not for long.

    No oxygen, no moisture and loaded with dust. So you are not going to burn. We are around 60% water so it boils, explosively in this case. So why don’t we see this if the temperature was 1000 degrees. Sorry to sound gory but we are talking brains and internal organs literally exploding.

    At a lower temperature it will still boil violently but probably not explosively. 250-300 is enough to sear the skin and (forgive me please) there are enough orifice to release the rapidly expanding water vapor……..ears, mouth included.

    We used to test sample of coal for what we called ‘volatile content’. To do this we heated one gram of coal at 900 degrees in an oxygen free atmosphere. This was a fast temperature rise. The essential shape of the coal did not change.

  32. #32 Ethan Bilke
    Joplin Schools
    May 14, 2013

    It is sad that people have to die in Volcanic Eruptions. If there was or could be one wish that would be to not have to suffer pain any or to not die in pain like the people that lived in Pompeii, Italy. It some times wants to make me wonder how much pain it would be to have to die in a volcanic eruption like the people in Pompeii.

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