Volcanic Eruptions: 79 AD Versus the Present ATOC 250: Natural Disasters Term Paper Abstract: Volcanic eruptions can be disastrous and deadly. It is, therefore, important to look back at prior eruptions and compare them to present eruptions in order to draw conclusions on what could be done to mitigate loss of life and destruction. The eruption of Mount Vesuvius in 79 AD on Pompeii and surrounding areas proved to be catastrophic because of the location of the volcano and especially since citizens were not aware that an active volcano was in their midst.
By examining the series of events that took place at Mount Vesuvius in 79 AD and comparing them to the impacts and forecasting of present day volcanism, one could draw better conclusions of the grandeur of the ancient eruption. After thorough analysis of scientific models, field data, and scientific journals, it is evident that the effects of the 79 AD eruption could have been lessened had roofing been better and had forecasting technology been where it is today.
However, had the 79 AD eruption happened today there could have been far worse economic implications on the aviation and leisure industries. The conclusion is that though forecasting technology has come a long way, it should be improved upon so that regional disasters such as the 79 AD eruption of Mount Vesuvius can be avoided. Introduction: Mount Vesuvius is infamous for its eruption in 79 AD when the volcano’s pyroclastic flows simultaneously destroyed and preserved the cities of Pompeii and Herculaneum.
Many details of this legendary eruption are derived from ancient literature and witnesses. Therefore, aside from examining literature and witness accounts, this paper will also look at research conducted by modern scientists in order to uncover more about its formation, composition and eruptions. In order to estimate the grandeur of the 79 AD disaster and to elucidate how its effects differed from present-day eruptions or could have been mitigated using modern techniques, this paper will also analyze more recent effects of volcanoes and modern predictive ethods. Overview of the problem: Mount Vesuvius is a Stratovolcano located on the Bay of Naples, Italy. It is the only European volcano located on the mainland to have erupted in the past 100 years. Two other major volcanoes in Italy are located on islands. This is a huge contributing factor to the great destruction caused to Pompeii and surrounding settlements by Mount Vesuvius in 79 AD. The ruination rooted from its close proximity to the 20,000 inhabitants of Pompeii as well as other inhabited settlements.
Though today the areas surrounding Mount Vesuvius are even more densely populated than in 79 AD, a settlement in the path of an active volcano is always extremely perilous. Today, Mount Vesuvius is encircled by three million inhabitants and is regarded as one of the most dangerous explosive volcanoes because it is the most populous volcanic region in the world (Marshall, 1906). The presence of cities and human activity at the base of an active and dangerous volcano is simply a plea for disaster if evacuation is not fast enough. The problem and sequence of events:
Before discussing the series of events for a specific volcano, it is important to examine its structure and composition. The present-day state of Vesuvius differs from its structure in 79 AD. The 79 AD explosion itself altered the shape of Vesuvius due to the explosive nature of that particular eruption. Mount Vesuvius is a Stratovolcano composed of alternating layers of ash and lava as well as pumice and tephra. This type of volcano can produce two different kinds of eruptions; the first is an eruption that ejects primarily ash and cinders, while the other type ejects lava.
Present-day Vesuvius has a large cone encircled by the rim of a summit caldera that began forming approximately 17,000 years ago. The large cone is in fact a product of the 79 AD eruption. (Vasallo, 2008) The magma has an intermediate to high viscosity and is composed of andesite. (Borade, n. d. ) Figure 1 This image shows Mount Vesuvius, reaching a height of 1,281 m above sea level at its highest point. It consists of the older volcano, a caldera, created by the collapse of its summit and the younger volcano, Vesuvius, which rises out inside of this caldera. Instituto Nazionale di Geofisica Vulcanologia, n. d. ) There was some precursory activity leading up to the climactic eruption of Mount Vesuvius in 79 AD. The volcanic eruption of Mount Vesuvius during the discussed period is known as a Plinian eruption, named after Pliny the Younger who was the only surviving witness of the events of 79 AD. (Sigurdsson, 1982) A Plinian eruption is known to be hugely explosive. In 62 AD, seventeen years prior to the eruption of Mount Vesuvius, the Bay of Naples and especially Pompeii suffered a destructive and powerful earthquake.
This earthquake is speculated to have been a sign that magma had moved up the volcano’s chamber towards the surface and fractured the edifice of Vesuvius. (Sigurdsson, 1982) An eyewitness from 62 AD, known as Seneca the Younger, reported ‘tainted air’ responsible for killing 600 sheep. Modern day scientists speculate that this ‘tainted air’ described by Seneca the Younger may have been Carbon Dioxide released by the volcano implying new activity from within Vesuvius, which in modern day society could have acted as a predictor of an oncoming eruption. Surrell, 2010) Another precursor involved a second foreshock in 64 AD. Suetonius Tranquillus and Tacitus, whom was senator at the time, reported this earthquake in separate accounts. (Tranquillus, 1914) Pliny the Younger wrote of more and more frequent tremors of the earth, which grew in recurrence until 79 AD. These earthquakes became so frequent that he wrote, “They are not particularly alarming because they are frequent in [Pompeii]”. (Pliny the Younger, n. d. ) Though the seismic activity persisted as magma was forced up the chamber of the volcano, this was not recognized as a warning sign during this era. Sigurdsson, 1982) The actual events that took place during the climactic eruption of Mount Vesuvius will be discussed through the analysis of a letter written by Pliny the Younger to Tacitus, the senator at the time. Also, reinterpretations done by present-day scientists will help unravel the events and eruptions of August 24th and 25th, 79 AD. Pliny the Younger described a giant cloud in the sky, which seemed to have been formed from, “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. ” (Pliny the Younger, n. d. ) According to modern day scientists’ reconstruction of these events, what Pliny the Younger witnessed was in fact the commencement of what would be an 18-hour Plinian eruption. An eruption column formed of pumice and ash rose above the crater to a height of approximately 20 km, which is consistent with the layer of pumice found in Pompeii around 79 AD. Pumice-fall was a huge threat to the population of Pompeii and surrounding areas.
The pumice was said to travel at terminal speeds of approximately 10 miles per second. The pumice posed two specific problems to the settlers; firstly, evidence shows that layers of pumice were up to 280 cm thick and had the ability to cause flat roofs to collapse and secondly, the air-fall phase caused darkness and made it difficult for citizens to get about outdoors. (Sigurdsson, 1982) This 18-hour Plinian phase of the volcanic eruption acted more as a warning to settlers than a death sentence, offering them the opportunity to flee before horror struck.
However, the fall of limestone and volcanic rock, about 9-11 cm in diameter, may have been damaging to humans and even fatal to those in its way. Not many samples of this type of rock were found; therefore, the chance of being hit by such a projectile was most likely rare. (Sigurdsson, 1982) Figure 2 This figure shows the thickness of the ash-fall in different regions around the volcano. It demonstrates how far the ash reached and also the areas impacted by pyroclastic flows, which will be discussed later.
Pompeii is one of the areas directly in the red section, so it was most affected by the eruption. (Oracle, n. d. ) Pliny the Younger further described harsh conditions including dark and thick skies, more tremors of the earth, and receding waters, “as though forced back by the tremors of the earth” (Pliny the Younger, n. d. ) Following these conditions, the next stage of the climactic eruption seemed to have kicked off in full throttle, “Then came an smell of sulfur, announcing the flames, and the flames themselves, sending others into flight but reviving [my uncle from his sleep]. (Pliny the Younger, n. d. ) According to scientists, the circumstances described by Pliny the younger such as increasing tremors and darkness are consistent with the climax of the Plinian stage of eruption. The receding waters described by the ancient witness are congruent with the prelude indicator of a tsunami. Tsunamis are often associated with volcanic eruptions due to extensive displacements of the sea floor or slumping of sea floor sediments caused by seismic activity. Scientists refer to the following events described by Pliny the Younger as the Pelean phase of eruption.
The fire and flames referred to previously are conjectured to have been pyroclastic density currents, also known as nuees ardentes, sweeping down the slope of Mount Vesuvius. This mixture was traveling down the flank of the volcano at a high velocity and was relatively denser and higher in temperature than the composition released in the previous Plinian phase. The nuee ardente that struck Pompeii and its citizens, who had not escaped in the previous 18 hours, was composed of two stages.
First, a ground surge, which ranged between 10-20 cm, followed by an inescapable pyroclastic flow ranging from 200 cm in thickness that buried and suffocated its victims, preserving fine details of their bodies in a delicate and powdery layer of ash. (Sigurdsson, 1982) To this day, body casts of victims from Pompeii who succumbed to the fury of the nuees ardentes still remain intact. Not much information remains concerning post-climactic activity because Pliny the Younger was writing to Tacitus in the context of the death of his uncle and anything subsequent to his uncle’s death was not discussed in the letter. Figure 3
This figure demonstrates the evolution of column height as well as associated events that occurred during the 79 AD eruption of Mount Vesuvius. The time scale assumes a constant rate of pumice-fall and is based on the information recounted by Pliny the Younger. (Carey, 1987) Cause of the problem: An interesting query involved with this particular volcanic eruption was the cause of the eruption and the cause of the sudden change in the composition of the magma as well as the transition from a Plinian eruption to a Pelean eruption. Multiple scientists investigated this query and most came to a concurrent conclusion.
External water played a large role in the volcano’s complex eruptive style. The Vesuvius eruption showed evidence of an eruption initially triggered by slight interaction between the magma from within the chamber and water. This generated a phreatomagmatic eruption, which is depicted in figure 3. (Hydrovolcanic Eruptions, n. d. ) Phreatomagmatic eruptions are characterized by much hydromagmatic activity, that is, magma-water interactions. The opening phase of the 79 AD Vesuvius eruption was followed by the Plinian stage, which was distinguished by increasing magma discharge and increasing eruptive columns.
As less water interacted with the magma within the chamber, there was a decrease in column heights, discharge rates and volatile, easily evaporated, content of the magma. As the volatile content of the magma decreased, it became denser. The hydromagmatic phase of eruption is associated with the high levels of lapilli found in the ash at Pompeii. (Rolandi, 1993) Figure 4 This image depicts the occurrence of a phreatomagmatic eruption in which magma reacts with ground water creating a steam explosion and ejecting shattered pieces of magma. (Hydrovolcanic Eruptions, n. d. )
Remedial action that could have been taken to predict or reduce the problem: The eruption of Mount Vesuvius in 79 AD clearly had massive impacts on Pompeii as well as other surrounding settlements. There are several known remedial actions that could have been taken to mitigate the effects of the eruption. However, the people of Pompeii were not necessarily aware that they lived in the midst of an active volcano because it had not erupted in approximately 1800 years. This kept them in the dark and gave them no time to take remedial action or to predict and understand the warning signs of an oncoming eruption.
Citizens may not have even known to flee when they saw smoke rise from the crater of the volcano. Initially, inhabitants were more intrigued by the phenomena than worried that an eruption was approaching. The seismic activity could have acted as a predictor had the people of Pompeii known that Vesuvius was in fact a volcano. (Wallace-Hadrill, 2010) After analysis of the horrific impacts of the eruption of Vesuvius on the urban environment of Pompeii, one could infer that proper roofing is crucial to survival in a similar scenario.
It is significant to note that 38% of loss of life in Pompeii, 79 AD, was due to roof and wall collapse. Flat roofs are subject to collapse from the accumulation of thick layers of pumice and ash, up to 5 m thick in the case of Pompeii, which spouted from the volcano into urban areas. Therefore, steeper roofs could have been a preventative measure taken by citizens in order to drain pumice and ash from rooftops and avoid over accumulation and subsequent collapse. (Luongo, 2003) Steepening the slope of roofs could have mitigated the loss of life in Pompeii.
Though at the time, citizens of Pompeii had a lack of knowledge and predictive technology, not much could have been done to avoid the high casualties resulting from this volcanic disaster. Due to the high velocity of the pyroclastic flows, even had inhabitants attempted to flee earlier on, there were no cars, or transport to aid in eluding the natural disaster. No matter where they were, the scalding pyroclastic flows would have engulfed and incinerated them to their death. (Luongo, 2003) Comparison to Present-Day Volcanism:
In present-day society, the actual eruptions of volcanoes have not altered all that much. However, forecasting methods as well as mitigation techniques have far improved since 79 AD. Volcanism also has several different as well as exaggerated effects on our society due to new technology such as aviation and also due to larger populations and the erection of more buildings. The first noticeable difference between volcanism in 79 AD and now is the forecasting knowledge and technology that society now has access to.
These technologies are still evolving and research is still in motion. However, forecasting gives us the ability to determine whether and when to evacuate a city or region before the volcanic eruption actually occurs based on cost-benefit analysis. In 79 AD, there were many warning factors that a primitive society could not recognize, but signals such as foreshock could have forewarned the people of Pompeii and significantly decreased loss of life. The complexity of the volcano makes determinism practically impossible, even with all the scientific break-throughs and technologies.
That is why scientists are experimenting with a “probabilistic volcano hazard analysis” in order to assess volcano risk. (Woo, 2009) Surveillance of the volcano as well as hazard mapping, which could not have been done in 79 AD, play a large role in the mitigation of damage and loss of life on account of volcanic eruptions. (Chester, 2000) Determining subterranean volcanic deformations may also aid in predicting when an eruption will occur because it indicates a change in subsurface magma. Earth-orbiting satellites as well as global positioning systems work together to provide hree-dimensional data on ground displacements. Though this evolving technology is extremely useful, it is limited in its functionality and is not so practical when it comes to Stratovolcanoes, like Vesuvius, because of their steeper slopes and complex structures. (Dzurisin, 2000) A second change since the 79 AD volcanic eruption in Pompeii has been urbanization, otherwise described as the movement of people from rural areas to cities. During the past 60 years, there has been a high concentration of people migrating to less economically developed regions.
This urbanization to less economically stable countries has increased global exposure to natural hazards such as volcanoes. (Chester, 2000) Lava flows, lahars, pyroclastic flows, as well as ash and tephra all have direct hazardous effects on nearby societies. People populate areas so close to volcanoes because of their multiple benefits, not because of their destructiveness. Volcanoes can increase soil fertility and can also become popular tourist destinations. (Lechner, 2002) A major eruption affecting a populated city may cause extreme damage if response time and forecasting is not fast enough.
This helps explain the large loss of life and damage done to Pompeii in 79 AD where forecasting technology was not available and the population did not know to flee. Now, with even larger populations settling near quiescent or active volcanoes and even more infrastructures, risk of damage is even greater. Volcanoes in present-day society are known to have adverse economic effects on the aviation industry. The implications of volcanic ash on aircraft safety are severe. In December of 1989, a Boeing 747 flying over Alaska lost power to all four engines and almost crashed on account of ash ejected from the nearby Mount Redoubt.
In the past 30 years, volcanic ash clouds have jeopardized more than 90 aircrafts. (Casadevall, 1994) A more recent example to demonstrate the huge impact of volcanoes on the airliner industry was during the low intensity eruption of Eyjafjallajokull in Iceland. During its eruption in April 2010, the airline industry took a hard hit and declared a no fly zone over many European countries. This caused them an estimated revenue loss of $1. 7 billion in US Dollars. (Mazzocchi, 2010) The effects volcanic ash could have on an aircraft are lethal.
Ash may cause the erosion of compressor blades. Also, since ash has a lower melting point than many other substances, when it gets sucked into the engine it melts and creates hot and sticky clumps that stick to the turbine blades and can stop them from functioning. (Vasko, 2010) Volcanoes clearly have grave economic effects on the airline industry and this was a technology that did not exist in 79 AD. An eruption of Mount Vesuvius today that produced large amounts of ash cloud could have enormous economic impacts on several industries.
Concluding Remarks: To conclude, since Mount Vesuvius is a volcano located on the European mainland in the vicinity of populated cities, in 79 AD it caused mass destruction and death to the people of Pompeii and surrounding settlements. The volcano started with a large Plinian eruption due to magma-water interactions in August of 79 AD and finished with a Pelean eruption that spouted destructive pyroclastic flows. Modern day scientists know several ways that the destruction caused by Mount Vesuvius to Pompeii could have been mitigated.
Damage could have been far palliated had their been better roofing, had people been aware that they were in the midst of a dangerous volcano and had they been mindful of the volcano’s precursors. In comparison to the 21st century, Mount Vesuvius could have been even more devastating today due to larger populations, more infrastructures, as well as the relatively recent establishment of the aviation industry. Scientists should continue their ongoing research of important forecasting technologies to improve hazard analysis and determine more precisely when exactly a volcano will erupt. Figure 5
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