The Eruption of Mt. Vesuvius
in AD 79
Why Vesuvius?
Mt. Vesuvius lies on a fault, a break in the earth’s
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
The Collision of the African and European Crustal Plates
The Bay of Naples from the Air (notice the size of Mt. Vesuvius)
A Subduction Zone
(from what two Latin words does “subduction” derive?)
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
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”)
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
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
Forms of Tephra: Ash and
Pumice
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
A Pyroclastic Flow
What Vesuvius
Might Have Looked
Like on the Day of
the Eruption
Reconstruction of the Vesuvius Eruption
The Eruption of Mt. St. Helens, United States, 1980
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