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)

(from what two Latin words does “subduction” derive?) 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