ERUPTIONS OF VESUVIUS ------------------- John Pazmino NYSkies nyskiesastronomy@earthlink.net 2005 June 24
Introduction ---------- Among the final free public lectures of the 2004-2005 season at Science, Industry, and Business Library was 'Future eruptions of Vesuvius' This was presented on Wednesday 22 June 2005 by Dr Flavio Dobran of Hofstra University. He is also active in 'Vesuvius 2000', an international effort to develop and implement a response plan for a reasonably foreseeable future eruption of this volcano.
Vesuvius ------ Vesuvius (it's just that, not 'Mount Vesuvius') is unusual for being a live volcano close to an urban region with a history of catastrophic blowups. It sits about 12 kilometers from central Naples, being a prominent feature of that town's landscape. Around the volcano is a dense suburban zone. The volcano is tiny compared to most other active ones, but it packs a wallop when it explodes. The small size allows population close in, within 6 kilometers!, before the slope is too steep to build on and travel around on. By the tens of our era, the Romans built up the region around Vesuvius for its fertile land, made so by the blanket of volcanic ash from prior, unrecorded, eruptions. Pompeii and Herculaneum were considerable towns, like those of mid America, with myriads of residents, thriving economy, and active culture. They sat 7 kilometers from the crater. A larger town, Neopolis, taken over from a Greek settlement, was about 12 kilometers away. This is present day Napoli in Italian or Naples in English. Today, about 600,000 souls reside within 7 kilometers of the peak, some 3,000,000 within 50. The latter includes all of Naples and its surrounds. Altho everyone knows about the volcano, they seem blase' about living so close to it. To visualize the situation of Vesuvius, let central Naples be at Bowling Green, Manhattan. The crater would sit near Randolph Sq (116th St & St Nicholas Av)! The proximity of built up land would reach up to the American Museum of Natural History and the Metropolitan Museum of Art!! It would also rank among the tallest peaks east of the Mississippi, some four times the height of the late World Trade Center.
The 79AD eruption --------------- The first records and most famous eruption is that of 79AD. For an early geological event, it was amazingly well documented in an objective fashion. This could be one of the first major catastrophes to be described without the 'biblical' narration of earlier eras. Perhaps this was due to the general maturity and cultural level of the Roman people? The dense population, even back then, produced accounts from various viewpoints and distances, assembling for us today a comprehensive picture of the eruption. Some of the writings of that event are still used today as reading assignment in lain classes! The area around Vesuvius was already known for its tremors. The entire Mediterranean Sea experiences earthquakes routinely so there was nothing abnormal about those around Vesuvius. Apparently there was an extra earth movement on 24 August 79ADD that alerted the populance to a potential major earthquake. They got a lot more. The volcano exploded suddenly. Within hours it wiped out myriads of people for a dozen kilometer around. Pompeii and Herculaneum were effaced. Excavations since then reveal the magnitude of the tragedy, some of which is open for tourists to inspect.
The 1631 eruption --------------- Since 79AD the volcano went to sleep. People moved back into the hazard zone, Naples grew into a major city-state by the Middle Ages. Much of the history was lost in the Dark Ages. On 16 December 1631 Vesuvius blew up again. This eruption was also incredibly well chronicled, this time with paintings and drawings and maps. The destruction leveled many new towns and erased thousands of lifes. One larger fatally hit town was San Sebastiano. There is some debate for the faithfulness of the depictions for this event. Some scientists argue that the spectacle was exaggerated. Others claim there was no need for extra hype. The eruption was one hell of a show on its own. Regardless, the accounts of the 79 and 1631 explosions are used to calibrate modern computer simulations of Vesuvius to an reasonable degree of confidence.
Some astronomy ------------ Dr Dobran didn't mention this, but I saw the connexion right away. The craters on the Moon were only just appreciated with the newly invented telescope. They resembled volcano craters on Earth, there being many known from old volcanos. In fact, there are a couple near Vesuvius! Surely, with the spectacle of the eruption before them, it took little mental exercise for people to conclude that the lunar craters were the result of volcanos. It would be over three centuries before any other cause for the lunar craters was seriously taken up! Not until the 1930s was the alternative, now probably the principal cause, studied: meteor and asteroid collision.
Mt St Helens ---------- The give and take of the audience compared Vesuvius with Mt St Helens. The capital difference is that Mt St Helens is in a wilderness region, well away from population centers. Yet, that peak is a skyline feature of both Portland, Oregon, and Seattle, Washington. These are large towns on the Pacific coast. While they were never in direct danger, the explosion was heard by them and caused mass anxiety. An other difference is that Vesuvius blew off verticly, like a cartoon volcano. Mt St Helens blasted out from one side. By the way, Mt St Helens is right now under a new pressuring, with venting of steam and ash. The show is a big tourist attraction from a safe distance away.
The next eruption --------------- Dr Dobran explained some simulations and studies to foretell when the next eruption may come, and its severity and extent. There really is no good way to reliably predict a volcano event. All that he and other geologists, can say is that Vesuvius WILL blow and cause incomprehensible devastation around it. Will this happen in the next couple decades? Later in this century? A couple centuries from now? With no credible predictive process in hand, it is hardly wise to issue alerts for evacuation or other defensive action. The squander of financial and human resources and the disruption of daily routine from a false alarm will for very many years kill the credibility of any future, perhaps real, alarm. And that constitutes the situation at Vesuvius. The bulk o Dobran's talk dwelled on the absolute need to provide for the eventual blowup of Vesuvius. There is nothing in place now, but some soft passive discussions and tuition in schools.
Vesuvius 2000 ----------- From time to time over the decades Italy studied ways to protect the inhabitants from a future Vesuvius eruption. For the most part, according to Dobran, they were inept and infeasible. Most of them were based on the presumption of orderly civil rule and integrity of escape routes. Neither can be counted on in a sudden catastrophe. For example, people could be assigned to take certain trains out of the danger zone. Lava or earthquake could easily break up rail lines. Rail crew could be killed or injured. Signals and power could be cut. And so on. The plans allowed that once the people were moved out of the danger zone, all was well and done. Now you have several hundred thousand homeless folk slapped onto an already populated region with no subsistence and no obvious return to their land. An other study called for gigantic civil works for penning or diverting lava flows away from the towns. Yes, believe it or not, such a project can be built, forgetting the expense and time. After the lava is contained, it will harden in place, removing the dikes and canals from possible later use. More immediately, the structures will for decades or centuries interfere with human activity near them. One bizarre schemes would purposefully make the danger zone unfit for habitation. No kidding. The state would withdraw social and civic functions, let services and facilities decay, abstain from keeping order and peace. Within a decade the people will on their own move out. Now you got a depopulated area around the volcano, to be fenced off, guarded, and patrolled. Vesuvius 2000 seeks to impress on Italy and other countries to take a more considered look at the Vesuvius situation. So far, nothing seems even remotely credible. It is plain impossible to move a million people on sudden notice to beyond 50 kilometers from Vesuvius within a few hours. That's the timescale of a potential warning of an eruption.
Other evacuations ---------------- I compared the case of Vesuvius with other evacuations. One that has intriguing parallels was the escape plan for a radiation discharge at Shoreham nuclear station. This, now dormant and never actually in operation, sits on the north shore of Long Island about as far out as Riverhead. The debates and arguments about shifting the inhabitants away from the station were, to be kind, ffulgescent. The warning, unlike for a volcano, would be pretty certain and timely. The problem was the utter lack of means to move the people away and the total disregard for their subsistence at their relocation sites. In the end, the futility of an escape plan prevented the station from ever getting into gear. It stands empty, cold, dark. Similar parallels can be made with hurricanes on the Florida Keys, earthquakes in Southern California, and, oh yes, the collision of a asteroid or comet.
The actual danger --------------- Most people think of a volcano for its flood of lava. Lava is melted rock, heated inside the Earth and poured out from the crater. This stuff definitely is dangerous for its heat and mass. However, lava tends to move slow enough to anticipate its path. You have time to evade or escape from it. Of course, the flow causes essentially unrecoverable damage by engulfing all in its path and then freezing into
solid rock. The greater hazard is the blast of superheated and poisonous gas that shoots down the volcano slopes. Traveling at hundreds of kilometers per hour and heated to around 1,000 degrees Celsius, this air instantly suffocates and internally sears anyone in its path. You can not see it coming nor have time to get away. Almost all the deaths of Vesuvius's previous blowups were from this gas. The downpour of ash causes few additional deaths, like burying injured people who can not climb out. It will impede rescue and recovery and will cause peripheral hazards. It clogs ventilation and heating systems, silts up harbors and canals, induces lung and throat ailments, grinds up machines and motors, contaminates water and fuel supplies. It caves in roofs, blankets roads, airports, rails, smothers farms, chokes animals.
Cost-benefit analysis-------------- ---- The Vesuvius case spotlights the problem faced where some disaster could inflict substantial human damage, yet people willingly and cheerfully live inside the danger zone. Why? There seems to be a balance between the perceived risk and prior experience. People don't mind frequent low-level disasters, like storm flooding. They don't mind cataclysms which occur once in millennia, like a tsunami or, ahem, volcano. Some where in between there may be a conscious ration for so-so hazard and so-so frequency. No one knows what this balance is or have to tilt it toward the safe side of action. The session winded down with crosstalk about disaster response, hazard determination, mass psychology, government competence, and other related subjects.