This page last updated on 03-Jul-2012 EENS 3050 Natural DisastersTulane University Prof. Stephen A. NelsonVolcanic Case HistoriesIn this lecture we will discuss three case histories of important eruptions that have occurred within recorded history. The eruption of Mount Vesuvius, Italy in 79 A.D., the eruption of Mount Pelée on the Caribbean island of Martinique in 1902, and the eruption of Mount St. Helens on May 18, 1980. Vesuvius, 79 A.D.Mount Vesuvius is located to the southeast of Naples, Italy along the Bay of Naples. Prior to the catastrophic eruption of 79 A.D. Vesuvius was considered an extinct volcano by the inhabitants of the area, who were flourishing at the height of the Roman Empire. The area northwest of Naples, known as the Phelegrean Fields, was known to be an active volcanic area, however. Nevertheless, when earthquakes became frequent in the Vesuvius area in 62 A.D., they caused no alarm because earthquakes were quite common throughout Italy. What we know of the eruption that took place in 79 A.D. comes from two different sources: (1) Two letters written by the Pliny the Younger, the nephew of Caius Plinius (Pliny the Elder), to the historian Tacitus concerning the death of his uncle. Pliny the Elder was an admiral in the Roman navy and well known in his time. (2) Information from geological and archeological studies that have examined the area around Vesuvius. We start with the account given by Pliny the Younger in his letters to Tacitus. About 1 P.M. on Volcanic Case Histories7/3/2012Page 1 of 8August 24, 79 A.D. the Plinys were in Misenum, about 30 km across the Bay of Naples from Vesuvius. A large cloud appeared above the volcano, growing rapidly, rising many thousands of meters and spreading out laterally in the atmosphere. Pliny the Younger states that the cloud had the shape of a Mediterranean pine tree, with a narrow trunk at the base, spreading out like branches above. Pliny the Elder was curious about the cloud and began to plan a trip across the bay to investigate. Before he could get his ship ready, he received word from people living closer to Vesuvius that people needed help, and his investigative mission became instead a rescue mission. He organized his fleet and set sail with the intention of rescuing people living near the base of the volcano at Torre del Greco. As he crossed the bay his ship was showered by hot ashes and pumice which accumulated on the deck. He soon found it was impossible to make the rescue attempt and he turned in the direction of the wind and instead landed at Stabiae, to the south of Vesuvius. At Stabiae, conditions were still mild and he encountered his friend Pomponianus who was trying to escape to the sea, but the winds were not favorable. In order to reassure Pomponianus that there was no danger, Pliny went to the local baths and sat down for a meal. As night came, Pliny retired for several hours of sleep. During his sleep tephra began piling up in the courtyard of the house and earthquakes and loud explosions occurred in the area of Vesuvius. Pliny awakened by the trembling and loud noises and conferred with Pomponianus. They decided that their best escape was to go to the shore and try to leave by ship. They tied pillows to their heads for safety from the falling pumice, but darkness enveloped the area as a result of the falling tephra, and it remained dark even after the sun should have come up. They eventually made it to the shore, but found that the wind was not blowing in a direction favorable to sail away from the area. Suddenly Pliny the Elder began to feel poorly. He laid down on a cloth near the shore and asked for water twice. Then sulfurous fumes descended on the area making staying put an unpleasant experience. Pliny rose to move away from the area, but fell dead. His friends thought that he had been poisoned by the fumes, but no one else was affected. His friends all later escaped. Three days later Pliny's body was found, unmarked by any damage. It is highly unlikely that Pliny died of poisoning from the fumes because Stabiae is so far from Vesuvius; it is more likely that he died from a heart attack resulting from his physical exertion in attempting to flee the falling ash. On the same morning that Pliny the Elder died, his wife and nephew were still in Misenum. Conditions there were also growing worse. Although Misenum was upwind from the volcano, there were still frequent earthquakes and the sky filled with ash and became dark. Pliny the Younger and his mother decided to leave their house and move farther away from the volcano. They set off in chariots, but the shaking of the ground and the accumulation of ash soon made it impossible to continue. They observed sharp retreats in the sea, followed by waves that crashed high on the shore, probably due to tsunamis as pyroclastic flows from Vesuvius entered the sea. They attempted to move farther inland, but soon the ash from the eruption became so thick that they were engulfed in total darkness. Pliny the Younger compared the darkness to that of a sealed room with no source of light. This lasted for many hours, but eventually the air cleared and they were able to observe Vesuvius in the distance. What had once been a smooth gentle mountain was now seen to be reduced in size by about one half, and what once had been lush vineyards in the countryside surrounding the mountain was now a plain of gray colored ash mantling the countryside like snow.The account given by Pliny the Younger says nothing about what happened to the towns of Volcanic Case Histories7/3/2012Page 2 of 8Pompeii and Herculaneum, close to the volcano. But his account of the "pine tree" like cloud above the volcano was the first description of an eruption column, and thus volcanic eruptions that produce eruption columns and fall deposits have taken on his and his uncle's name, and are referred to as Plinian eruptions.The fate of Pompeii and Herculaneum had to await further exploration by geologists and archeologists. Note that Pompeii was located about nine kilometers down wind from Vesuvius, and was buried by close to 3 meters of tephra that had fallen from the eruption cloud. Since the eruption killed most of the inhabitants of Pompeii it remained abandoned for hundreds of years. In 1595 some of the ruins of Pompeii were discovered when excavation for a new aqueduct began. Coins were found, along with marble tablets with inscriptions