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Volcanic Eruptions
Mt. Vesuvius (79AD) – Pompeii
Prepared by Karissa Lee
What is a volcano?
• A volcano is a vent or
'chimney' that connects
molten rock (magma) from
within the Earth’s crust to
the Earth's surface.
• The volcano includes the
surrounding cone of erupted
material.
How and why do volcanoes erupt?
• Hot, molten rock (magma) is buoyant (has a lower density
than the surrounding rocks) and will rise up through the crust
to erupt on the surface.
• Depending how magma reaches the surface, how easily it
flows (viscosity) and the amount of gas (H2O, CO2, S) it has in
it, determines how the volcano erupts.
• Large amounts of gas and a high viscosity (sticky) magma will
form an explosive eruption!
• Small amounts of gas and (or) low viscosity (runny) magma
will form an effusive eruption, non-explosive.
• Lava flows when magma trickles out of the volcano (lava flow).
Effusive and Explosive Eruptions
• Effusive Eruptions
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Occur when hot, (1200 °C )
runny basalt magmas reach
the surface. Dissolved gases
escape easily as the magma
erupts, forming lava that
flows downhill quite easily.
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Lava flows generated by effusive
eruptions vary in shape, thickness,
length, and width depending on
the type of lava erupted,
discharge, slope of the ground
over which the lava travels, and
duration of eruption
Kilauea Volcano, Hawaii. Lava
spilling from the cone has formed a
series of lava channels and flows.
Effusive and Explosive Eruptions
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Explosive Eruptions
• Explosive volcanic eruptions is usually
catastrophic
• Erupts 10’s-1000’s km3 of magma
• Send ash clouds >25 km into the
stratosphere
• Have severe environmental and climatic
effects
• Very Hazardous
•
Three products from an explosive eruption
• Ash fall
• Pyroclastic flow – A fast moving hot gas
and rock with up to 450 mph speed and
up to 1,000 °C temperature. This usually
travels downhill by gravity, which can
easily bury the highly populated areas
under the mountain
•
Pyroclastic surge - a fluidized mass of
turbulent gas and rock fragments which is
ejected during some volcanic eruption
Above: Large eruption column and
ash cloud from an explosive
eruption at Mt Vesuvius, Italy in
March 1944
More About Pyroclastic Flows
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Burns and buries such a wide range of region
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Flood and Mud Slides
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Hot volcanic activity can melt snow and ice
Melted snow and ice picks up rock and debris
Forms fast flowing, high energy torrents
Destroys all in its path
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Ash Builds Up
• Collapses roofs
• Brings down power lines
• Kills plants
• Contaminates water supplies
• Respiratory hazard for humans and animals
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Vesuvius (AD79) eruption had pyroclastic flows with the above occurrences.
Background
Mt. Vesuvius (AD79) - Pompeii
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Mt. Vesuvius is located seven
miles from the city of Naples in
Italy.
The height of the volcano has
changed greatly for 200,000 years.
It stands today at 1277 meters in
height with a base that is 48
kilometers wide.
On August 24, 79AD Mount Vesuvius
literally blew its top, erupting tons of
molten ash, rocks, pumice and sulfuric
gas miles into the atmosphere and it
continued about 19 hours.
Mt. Vesuvius is a composite type of
volcano, which is formed by alternating
layers of lava and rock fragments
The black cloud represents the general
distribution of ash and cinder
Negative and Positive Effects of Eruption
Mt. Vesuvius (AD79) - Pompeii
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Negative Effects
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It was an explosive eruption that
followed by Pyroclastic flows of
poisonous gas and hot volcanic
debris engulfing the cities of
Pompeii, Herculaneum and Stabiae,
suffocating the inhabitants and
burying the buildings.
Positive Effects
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The cities remained buried and
undiscovered for almost 1700
years until excavation began in
1748. These excavations continue
today and provide insight into life
during the Roman Empire.
Interesting Facts
Mt. Vesuvius (AD79) - Pompeii
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The people of Pompeii and Herculaneum had
plenty of warning signs way before the eruption.
Some but not many did escape in time.
Most were overcome by the gasses before the
actual eruption.
Because ash covered the sky, the visibility was
so poor that people were disoriented and
stopped in their tracks.
The weight from the ash and debris collapsed
most rooftops
Mt. Vesuvius has been rumbling for years and no
one took it seriously.
Many tried to escape by sea but were overcome
by the debris falling and many were found dead
in caves along the coast.
The forms of where bodies once lay were
discovered when an excavator poked a rod into
the ground and realized there were hollow
cavities.
Food, tools, paintings, and many other items
were discovered under the packed and hardened
ash.
People today are still living quite near this
rumbling mountain with it's rich, fertile soil.
Vesuvius Today
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The areas of Vesuvius was
declared as a national park in
1995 by attracting thousands
of visitors worldwide
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Vesuvius is still regarded as
an active and the most
dangerous volcano in the
world because it is located
nearby heavily populated
flanks:
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around 1.5 million people live
in the city of Naples alone
Naples is situated approx. 30
km from Vesuvius
Pyroclastic flows can flow up
to 100 km from source
THANK YOU
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References
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http://en.wikipedia.org/wiki/Volcano
http://library.thinkquest.org/03oct/01550/eruptions.htm
http://kids.discovery.com/tell-me/curiosity-corner/earth/naturaldisasters/why-do-volcanoes-erupt
http://en.wikipedia.org/wiki/Explosive_eruption
http://en.wikipedia.org/wiki/Effusive_eruption
http://en.wikipedia.org/wiki/Vesuvious#Eruption_of_79
http://www.windows2universe.org/earth/interior/Mt_Vesuvius_ad79.html
http://www.lovethesepics.com/2011/10/infamous-mount-vesuviusone-of-the-worlds-most-dangerous-volcanoes-41-pics/
http://vulcan.fis.uniroma3.it/vesuvio/79_eruption.html
http://www.bbc.co.uk/dna/ptop/A28303968
http://en.wikipedia.org/wiki/Pyroclastic_flow