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Mount Vesuvius

by Alex Loeb

 

http://volcano.und.nodak.edu/vwdocs/volc_images/img_vesuvius.html

Mount Vesuvius, the only active volcano in continental Europe and maybe the most well known volcano worldwide is located near Naples, Italy. This picturesque and dangerous volcano is responsible for the most catastrophic eruption the world has ever seen in 79 A.D. The enormous eruption wiped out the cities of Pompeii and Herculaneum and killed of upwards of 16,000 people.  Besides it most devastating eruption in 79 A.D., Mount Vesuvius has erupted 200 times since, each time with devastating affects. The fascination with Mount Vesuvius likely stems from its eruption in 79 A.D. being the first documented eruption. As a result, citizens through reading could understand for the first time the enormity and incredible destruction of volcanic eruptions, but more importantly scientists have used Mount Vesuvius as a basis of volcanic study. (Vulcan’s Fury)

 

The interaction between continental plates floating on the surface of the mantle creates mountains and volcanoes. Mount Vesuvius was created through the convergence of two tectonic plates, the African plate pushing beneath the Eurasian plate, which pushed upward and created a submerged deep ocean volcano in the Bay of Naples.  Converging plates are typically responsible for the creation of volcanoes. Later, Mount Vesuvius emerged from the ocean as an island and over time has connected to the mainland due to the buildup of deposits from its eruptions. (Volcanoes)

 

http://pubs.usgs.gov/publications/text/understanding.html

Mount Vesuvius’ volcanic behavior originates deep below the earth’s surface.  4.6 million years ago earth formed from a cloud of dust and gas; the heat on the surface of earth cooled but the fiery rock on the inside did not.  The fiery rock, or the mantle, over time has gained heat from gravitational energy and radioactive decay. When the converging plates collide and then gradually separate, magma from the mantle, or molten rock, seeps up through the cracks and rises to the surface. The other way magma emerges is when other plates converge together and through fiction creates heat which melts the molten rock. This molten rock rises up from the magma chamber of Mount Vesuvius and into the atmosphere because it is less dense then the surrounding rock. (Volcanoes)

 

Mount Vesuvius standing 4190 feet tall is a composite volcano composed of a mix of layers of lava flows, volcanic ash, and cinders. It consists of a volcanic cone, called Gran Cono, that was built inside a summit caldera , called Mount Somma.

 

http://vulcan.fis.uniroma3.it/vesuvio/gifs/conoaer.gif

A caldera is a volcanic depression usually circular in form and caused by a collapse of the magma chamber after a large eruption. Composite volcanoes, or stratovolcanoes, like Mount Vesuvius and other famous mountains such as Mount Saint Helens in Washington state and Mount Fiji in Japan are usually massive, steep sided mountains. Convergent plate boundaries are most associated with the formation of composite volcanoes. (Volcanoes) The distinguishing characteristics of composite volcanoes are the large craters or multiple vents on the top of the mountain that release the magma from the earth’s crust.  Mount Vesuvius is a complex volcano with many major and minor volcanic centers. The other two types of volcanoes are shield volcanoes which release fast moving, less viscious basaltic lava and cinder cone volcanoes that release high viscosity, slow moving andesitic lava. Basaltic lava, reddish yellow in color, and andesitic lava, dark gray or brown in color, emerge from below ground around at a temperature around 1200 degrees Celsius.  In appearance, basaltic lava is smooth and takes pillow-like form whereas andesitic lava is blocky.  Contrastly, Mount Vesuvius like other composite volcanoes releases both basaltic and andesitic lava from its major and minor volcanic centers. This lava hybrid adds to the danger of Mount Vesuvius because during eruption it emits flows of smooth lava like shield volcanoes and has pryoclastic explosions that blow large amounts of rock and debris into the air. (“Pyroclastic Flows,” Encyclopedia of Volcanoes)        

 

1971 Eruption

http://volcano.und.nodak.edu/vwdocs/volc_images/img_vesuvius.html

Mount Vesuvius has erupted at least 200 times, most recently in 1944, but is most remembered for the eruption at 1:00 P.M. August 24th in 79 A.D which destroyed the city of Pompeii and claimed thousands of lives.  Romans scholars, including Pliny the Younger, witnessed and described the catastrophe in writing. Mount Vesuvius, like many volcanoes offered premonition that disaster was going to strike. Months preceding the eruption ground around the volcano swelled and there were numerous small earthquakes. Although there were warnings, the citizens of Pompeii did not understand their significance. (Vulcan’s Fury )

 

Fragments of rock and lava, or tephra, fell for a day straight after the pyroclastic eruption and covered Pompeii. During the pyroclastic eruption, a fast moving cloud of ash and lava fragments carried through the air, engulfed citizens and flattened the city. The pyroclastic eruption created a huge mushroom cloud consisting of three regions. From bottom to top: the gas thrust, convective, and umbrella regions. In the gas thrust region, expanding gas in the magma determines the type of eruption and magnitude of the explosion before the magma ascends from the magma chamber. The convective region, directly above the gas thrust region is to a hot air balloon. Just like a hot air balloon, the plume retains its buoyancy by the heating of entrained air. The tephra, ash, and atmospheric gases remain airborne in the plume since their combined density is the less than that of the ambient atmosphere. Lastly, the umbrella region, or top of the plume, is the point in which the plume has equal density to the surrounding atmosphere and begins to horizontally spread and resemble a mushroom cloud.  (Volcanoes)

 

Volcanoes, second edition

 

http://volcano.und.nodak.edu/vwdocs/volc_images/img_vesuvius.html

The 20,000 residents of Pompeii, many who lived in close proximity to Mount Vesuvius because of the fertile land, faced a difficult decision the day of the pyroclastic eruption, either stay and hope the shower of hot ash and pumice subsided or attempt to flee. (Mount Vesuvius) The pumice and ash fell for eighteen hours straight and chaos continued through the night into the following morning. Those citizens fortunate enough to flee accounted for almost all of the survivors. After the onslaught of explosions, twelve feet of pumice and ash covered Pompeii. The decimation of Heruclaneum, Pompeii’s sister city, occurred shortly after as a result of a massive cloud of steam and mud that completely enveloped they city.  Herculaneum’s destruction was even more devastating than Pompeii’s. Like in Pompeii, hundreds of Herculaneum’s citizens were discovered in a hardened molten cast.  (Vulcan’s Fury)

 

Two days later on August 26th the sky finally cleared, ash blanketed the 300 kilometers around Mount Vesuvius and destroyed everything. In both Pompeii and Herculaneum there were no more trees, buildings, villages, animals, but most shocking, people.  It was as if the cities of Pompeii and Herculaneum never existed. A city was later built on top of Pompeii however luckily for archaeologists hundreds of years later much of both cities were preserved buried beneath the ash. Because of the preservation the public today can visit Pompeii and many of the ruins.  (Vulcan’s Fury)

 

Even though Mount Vesuvius is most remembered for its destruction of the Roman city of Pompeii, it is still an active volcano. Long calm periods are usually a sign that an eruption cycle is due. After two sizeable eruptions in 472 and 532 A.D., there was a period of quiescence before the next significant eruption in March of 1631. In 1631, 3,500 residents died in and around Naples from the fast moving lava and mudflows. The last eruption occurred in 1944 when the conelet collapsed and a lava flow was emitted which eventually reached villages below. After the lava flow, a small pyroclastic explosion took place and a plume formed. Although again this eruption was devastating to the surroundings, it had an interesting historical impact. In March of 1944 the arrival of the allied forces in WWII coincided with the eruption of Mount Vesuvius. As a result, lava flows from Mount Vesuvius destroyed fighter airplanes stored by the allies east of the volcano. (“History of Eruptions”)

 

Mount Vesuvius has erupted sporadically for hundreds of years and shows no signs of letting up. For volcanologists this presents a challenge of predicting when the next eruption may happen. Volcanologists continue to make progress in predicting eruption however it remains in inexact science. Magma shifting underground which may cause small earthquakes and the magma underground making bulges in the sides of the volcano are usually good indicators. Also, changes in chemicals emitted from the volcano also help predict eruptions. Nevertheless, the one million people living in and around Naples still face a danger that Mount Vesuvius will strike again with devastating results. (Volcanoes)

 

Bibliography

Sigurdsson, Heraldur. “Pyroclastic Flows.” pp. 572-579. Encyclopedia of Volcanoes.   New York: Academic Press, 2000

Francis, Peter and Clive Oppenheimer. Volcanoes. pp. 17-53, pp150-156, and pp. 481-490. New York: Oxford University Press, 1993, 2nd Edition.

Scarth, Alwyn. Vulcan’s Fury. pp18-41. London: Yale University Press,  1999.

Lobley, Logan. Mount Vesuvius. Roper & Drowley, 1889.

“History and Eruptions.” Vesuvioinrete. 14 April 2004 <http://www.vesuvioinrete.it/e_storia.htm>