6.2.09 Geo. – “Pompeii, the last day.”
In AD79, 2 000 years ago a devastating natural disaster struck the ancient world. The city of
Pompeii (in Italy) was destroyed by the eruption of the volcano, Mount Vesuvius. A town
nearby, Herculaneum was also destroyed by the same eruption, but the affects were
different.
Using evidence from a number of sources they found out the details of the last day and how
the volcano erupted. The evidence they used came from:
 Casts of the victims (people and animals) buried in the ash
 precious (expensive or rare) objects that gave details
 The writings of a young man, Pliny the younger who watched the events happening
from across the bay
Pompeii street (Note: Mount Vesuvius in the
background. Amazing how something so
beautiful can cause such death and destruction)
Mt. Vesuvius
Eerie plaster casts of Pompeii residents at their moment of death.
Human remains preserved intact. People are piled on
top of each other. Note the difference between
Herculanian remains and Pompeiian remains. Isn't it
amazing what difference a few miles can make?
(Encyclopaedia Online)
Lava, ash, and extreme temperatures disintegrated the
bones, skin, and internal organs, leaving pockets of gas
where a person had once been. Plaster was poured
into the air pockets and so today we can see plaster
casts of people frozen at the time of death.
surge - in a volcanic eruption, a fluid (liquid) mixture of hot rock
pieces, hot gases, and trapped air that moves at high speed in thick,
gray-to-black, turbulent clouds that hug the ground.
 The temperature of the volcanic gases can reach about 600
to 700 °C.
 The velocity (speed) of a flow often exceeds 100 km per
hour and may reach speeds as great as 160 km per hour.
 Flows may even travel some distance uphill when they
have sufficient speed, due to the force of a lateral blast out of the side of an exploding
volcano.
 Reaching such temperatures and velocities, flows can be extremely dangerous.
The volcano begun to erupt - why? how?:
 There was a weak area in the earth’s crust
 A thick plug of rock blocks the exit
 Explosive pressure mounts
 The land above swells and the earth shakes (earth tremors)
 It is like a super-heated pressure pot
 Molten rock turns to foam (bubbles)
 This forms a churning (turning, spinning) column of
superheated rock and gas that rises up 15m into the air.
 It goes dark from the cloud of ash.
 Boiling rock mixes with air and cools, then solidifies. The
magma is full of air
 It begins to fall down as light pumice stones but mixed with it is
deadly, dense rocks from deep inside the volcano.
 They fall at 200km/hour and kill/injure people below.
 Pumice and ash suck moisture from the air – people have dry mouths and throats.
 Heavy with denser rock, part of the volcano collapses and a pyroclastic surge speeds
down the sides of the volcano.
 This pyroclastic material is 5 times hotter than boiling water so it burns everything in
its way.
 The heat is so great (intense) that death is
instant and people’s bodies are turned to
charcoal if they are outside.
 People who are inside buildings die from
thermal shock. Their soft tissues (skin, organs
etc) are turned to vapour (vaporised), teeth and
bones are shattered, brains are boiled and
explode.
 Next the magma chamber collapsed (fell in)
 This started another pyroclastic surge travelling
at more than 100km/hr
 Clouds of toxic gases went through the town
(carbon dioxide suffocated people and
Hydrogen chloride gas burned their throats and
eyes).
 People’s lungs filled with fluid from the hot
gases
 The fluid (liquid) mixed with ash to make a
kind of cement in their lungs
 They couldn’t breathe, and suffocated to death.
 In 18 hours, 10 million tonnes of volcanic ash fell.

Victims’ bodies were preserved by the ash surrounding them.
Plinian eruptions – named after Pliny – are very explosive pyroclastic surges. They only
happen on this scale (as great as this) every 2 000 years. Another is thus due now.
Advantages of volcanoes and why people still live there (3 500 000 in Pompeii today):
 Fertile soil land that is good for farming – it has rich soil, full of minerals.
 Good fishing
 Tourism
 Thermal power
 People grew up there, it is beautiful and they don’t believe there will be another
eruption.
In Iceland there are many hot springs:
Geothermal springs are tapped to generate
energy and as a source of hot water for
Icelanders' homes. Water from the plants also
feeds nearby thermal spa baths, such as the
famous Blue Lagoon, where the warm waters
are rich in minerals like silica and sulphur.
Pyroclastic Surges are fast-moving clouds of hot ash
that travel with the pyroclastic flows. These surges
can separate from the pyroclastic flows and even travel
uphill.
See:
http://www.bbc.co.uk/scotland/education/int/geog/envhaz/volcanoes/cause/features/index.sht
ml?factor=surge
Pyroclastic flow
A series of pictures showing the movement of a
small pyroclastic flow shed from the margins
of the growing dome (in cloud) on Montserrat
in 1997.
The photos were taken only a few seconds
apart.
The flow looks like ground-hugging grey
smoke, but consists of a mixture of gas, ash,
and dense hot lava blocks.
The shroud of ashy cloud conceals the dense
interior, and in fact sometimes separates from
the dense part to form a less dense, more
mobile current called a pyroclastic surge.
Pyroclastic surges are dense clouds of hot gas
and rock debris that are generated when
water and hot magma interact. They are more
violent and travel much faster than pyroclastic
flows; surges have been clocked at over 360
km/h. They are extremely destructive because
of their high density and high speeds. People
and structures in their path have little hope for
survival.