The Eruption of Mt. Vesuvius in AD 79

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The Eruption of Mt. Vesuvius in AD 79
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Why Vesuvius?

• Mt. Vesuvius lies on a fault, a break in the
  earths crust between the African crustal plate
  and the European crustal plate
• This break results in magma, or molten rock,
  being forced up to the surface of the earth where
  one of the plates is being pushed under the other
  in a process known as subduction
• This region is therefore prone to earthquakes and
  volcanic activity

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The Collision of the African and European Crustal
Plates
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The Bay of Naples from the Air (notice the size
of Mt. Vesuvius)
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A Subduction Zone (from what two Latin words
does subduction derive?)
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Mt. Vesuvius

• Mt. Vesuvius is a stratovolcano, a volcano built
  up with layers of magma that create steep sides
  this creates the potential for violent eruptions
• Mt. Vesuvius had erupted several times in early
  Roman history, but Romans kept no records of it
  it had not had a large eruption since 1800 BC and
  was building a large magma chamber to breed a
  catastrophe

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August 24, AD 79

• Earthquakes were the first sign of Vesuvius
  activity in the weeks prior to August 24, AD 79
• Prior to that, Vesuvius was simply regarded as a
  mons (a mountain) that was suitable for growing
  grapes because of the rich volcanic soil
• It was named for Hercules, son of Zeus, who was
  also known as Ves (in Greek Vesuvious would mean
  Son of Zeus)

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August 24, AD 79

• The eruption began about 1 pm when a giant column
  of smoke and ash rose in an explosion from the
  volcano
• Soon afterwards, small light stones called pumice
  and heavier stones fell out of the sky at over
  100 miles per hour
• The weight of them could cause a headache (ouch!)
  or collapse roofs
• The material ejected is collectively known as
  tephra

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The Perfect Storm

• As ash blanketed the sky, a wind blowing across
  the bay kept the ash hovering over Pompeii
  instead of blowing it out to sea
• People began to flee to the shore in hopes of
  escape but rescue was not coming
• Poisonous gases escaped from the volcanic vent,
  the most deadly of which were carbon dioxide and
  hydrogen chloride
• Across the Bay of Naples, in Misenum, a young
  Pliny with is uncle, the Elder Pliny, watched the
  growing disaster

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Forms of Tephra Ash and Pumice
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Death Comes

• During the 19 hour eruption cycle, Vesuvius
  expelled 1 cubic mile of material
• The most deadly material came in the form of a
  pyroclastic flow a superheated cloud of gas and
  ash that came from the collapsing eruption
  column it rushed down the side of the mountain
  at 60 kilometers an hour with a temperature over
  600 degrees farenheit
• This pyroclastic flow carbonized humans in its
  path, causing their brains to explode out of
  their heads

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A Pyroclastic Flow
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What Vesuvius Might Have Looked Like on the Day
of the Eruption
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Reconstruction of the Vesuvius Eruption
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The Eruption of Mt. St. Helens, United States,
1980
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The Finale

• The eruption ended on August 25th with the final
  collapse of the eruption column blanketing
  Pompeii and nearby cities with ash
• Approximately 3,000 people were killed
• Because their remains were carbonized, their body
  forms were left in the ash for archaeologists to
  study in the 20th century the eruption had both
  destroyed and saved a town