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Volcano-Mt. Vesuvius
Crystal Crow
Physical Geology
Fall 2005

                                            Mount Vesuvius, Italy

                                              Vesuvius is a 10,000-year-old composite volcano. The volcano overlooks Naples, Italy. Vesuvius has erupted two hundred times in a span of two thousand years, and is still considered active. The volcano is famous for the destruction of Pompeii and Herculaneum.

 Mt. Vesuvius, Italy

and U.S./Japan ASTER Science Team

Vesuvius lies on a fault line that is caused by the subduction of the African Plate lying beneath the Eurasian Plate. Because of this subduction the Mediterranean Sea is becoming smaller and the Apennine Mountains are being uplifted. About 1.9 miles under the volcano lay the magma chamber. When the magma grows it starts off a series of earthquakes. Prior to the A.D. 79 eruption there were a series of earthquakes ranging from 4 or 5 on the Richter scale.

The crater of Vesuvius. All photographs courtesy of and copyrighted by Mike Lyvers.

                        The Eruptions of Mt. Vesuvius:

   There are three types of eruptions that Vesuvius has shown:
      Strombolian-Vulcanian eruptions

          Happened in the years 1906 and 1944.
          The explosions range from small to medium in size.
          The eruptions are either effusive or explosive-effusive.
          There were local heavy tephra falls, major lava flows, and small pyroclastic flows that were restricted to the cone of the volcano.
      Subplinian eruptions

          Happened in the years A.D. 472 and 1631.
          There were explosive eruptions. Heavy tephra fall was around the volcano with pyroclastic flows and surges.      C)C)       Plinian eruptions
          Very violent explosions
          Widespread tephra fall with major pyroclastic flows and lava flows. 

Photo by Italian Air Force from Green and Short (1971). 

What happened to Pompeii:

5 Feb A.D. 62: Pompeii experiences a severe earthquake. The earthquake causes damage to both the buildings and the majority of the city.

20 August A.D. 79: Pompeii is hit again with a less severe earthquake. The citizens have no idea what will come next.

24 August A.D. 79: Between noon and 1pm Mt. Vesuvius erupts sending a 12 mile high cloud of ash and rock into the air and blocking out the sun. This description is portrayed in a letter by Pliny the Younger; a witness to the destruction. The wind, blowing from the Northwest, sends volcanic matter to Pompeii, Herculaneum, Stabiae, and other southeast towns. The eruption triggered lightning, which was caused from the ash and other atmospheric disturbances being thrown into the air. Piles of ash, pumice, and rock fell filled up the streets; open spaces; and rooftops, causing injuries. This phase lasted all day.  Some people had escaped while others chose to stay.

25 August A.D. 79: Sometime after midnight the Pelean phase (2nd phase) brought magma surges, volcanic mud, and pyroclastic surges.

 Ten feet of tephra covered Pompeii. 

These skeletons were found in a boathouse off the shoreline in Herculaneum. 

What happened in Herculaneum:

Herculaneum was situated at the base of the volcano. The city was hit by a pyroclastic surge and buried within the volcanic mud. At first, the city was out of harm's way until the column of the volcano collapsed creating a pyroclastic flow of hot ash. The surge swept down the western part of the volcano, thus destroying Herculaneum. Due to the hot ash the citizens were burned, battered, and had suffocated. 75 feet of ash buried the city of Herculaneum.  

Interior part of a house in Herculaneum. 

Pompeii would have been hit by the same amount of the surges, but their northern wall had stopped them. Around 7.30 am, a pyroclastic surge was able to roll over the wall due to the accumulated ash, pumice and other volcanic matters. The surge killed everything in sight. The people who had stayed were baked by the hot air that had come from the surge.  Both Pompeii and Herculaneum were buried for 1700 years.

                      The mold of a dog is shown in the above photo.  It was chained and had died from the ash.

                     Other dates:

                       After Pompeii was destroyed, the volcano continually erupted every 100 years until roughly
                       1037 A.D., when it became dormant for 600 years.                      

                       A.D. 475: High explosive Plinian eruption.

                       1631: A series of earthquakes begin 6 months before the explosion.

                       During the restoration, workers found the ruins of Pompeii, 1600 years after its destruction.
                       Herculaneum would be found 300 years later.

                       16 December 1631: Around midnight there is a large explosion. This lasted for two days. 
                       There were some volcanic activity (lahars, lava, and ash) that continued until January 1632.

                      13 March 1944: This is the last of eruptions from Mt. Vesuvius.  

                      There was volcanic activity ranging from 6 months to 30 years, and a dormant time ranging
                      from 1.5 years to 7.5 years. These periods had lasted for about three centuries before
                      completely stopping in 1944.

                  The rocks at Mt Vesuvius are tephrite.  Tephrite has a basaltic character and contains calcic plagioclase, augite, and nephline.

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