Eruptions of Mt. Vesuvius Mt Vesuvius and Naplesacademic.brooklyn.cuny.edu/geology/powell/courses... · 79 AD Eruption of Vesuvius August 24 or 25 Explosive eruption that lasted 19

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Eruptions of Mt. Vesuvius

Eruptions of Mt. Vesuvius

Historical and Future(?)

Historical and Future(?)

Tragedies

Tragedies

CC 3.32, Lecture 3

CC 3.32, Lecture 3

Location of Mt. Vesuvius

Location of Mt. Vesuvius

Mt Vesuvius and Naples

Mt Vesuvius and Naples

Ruins of Pompeii

Ruins of Pompeii

79 AD Population: ~20,000

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Casts of Bodies in Pompeii

Casts of Bodies in Pompeii

1,150 bodies have been uncovered

79 AD Eruption of Vesuvius


��Vesuvius had not

Vesuvius had not

erupted violently in

erupted violently in

prior history

prior history

��Minor eruption in 217

Minor eruption in 217

BC (Plutarch)

BC (Plutarch)

Precursor Signs:

Precursor Signs:

��Earthquakes

Earthquakes

��Drying of wells and

Drying of wells and

springs in early

springs in early

August, 79 AD

August, 79 AD



��August 24 or 25

August 24 or 25

��Explosive eruption

Explosive eruption

that lasted 19 hours

that lasted 19 hours

��1 cubic m

ile of ash

1 cubic m

ile of ash

erupted

erupted

��Ash column was 20

Ash column was 20

miles high

miles high

��Winds blew southward

Winds blew southward

••10 feet of ash fell on

10 feet of ash fell on

Pompeii

Pompeii



by Pliny the Younger


��““The cloud was rising from a

The cloud was rising from a

mountain

mountain-- at such a distance

at such a distance

we couldn't tell which, but

we couldn't tell which, but

afterwards learned that it was

afterwards learned that it was

Vesuvius. I can best describe

Vesuvius. I can best describe

its shape by likening it to a

its shape by likening it to a

pine tree. It rose into the sky

pine tree. It rose into the sky

on a very long "trunk" from

on a very long "trunk" from

which spread some

which spread some

"branches." I imagine it had

"branches." I imagine it had

been raised by a sudden

been raised by a sudden

blast, which then weakened,

blast, which then weakened,

leaving the cloud unsupported

leaving the cloud unsupported

so that its own weight caused

so that its own weight caused

it to spread sideways. Some

it to spread sideways. Some

of the cloud was white, in

of the cloud was white, in

other parts there were dark

other parts there were dark

patches of dirt and ash.

patches of dirt and ash. ””

Vesuvius

1944

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��““Ash was falling onto the ships

Ash was falling onto the ships

now, darker and denser the

now, darker and denser the

closer they went. Now it was

closer they went. Now it was

bits of pumice, and rocks that

bits of pumice, and rocks that

were blackened and burned

were blackened and burned

and shattered by the fire

and shattered by the fire””

��““The ground outside his room

The ground outside his room

rose so high with the m

ixture

rose so high with the m

ixture

of ash and stones that if he

of ash and stones that if he

had spent any m

ore time there

had spent any m

ore time there

escape would have been

escape would have been

impossible

impossible……They tied pillows

They tied pillows

on top of their heads as

on top of their heads as

protection against the shower

protection against the shower

of rock. It was daylight now

of rock. It was daylight now

elsewhere in the world, but

elsewhere in the world, but

there the darkness was darker

there the darkness was darker

and thicker than any night .

and thicker than any night . ””

Plinian

PlinianEruptions

Eruptions

��Large, explosive events

Large, explosive events

��Eject enorm

ous columns of

Eject enorm

ous columns of

ash (>11km tall)

ash (>11km tall)

��Ejecta

Ejecta

is carried by the

is carried by the

prevailing winds

prevailing winds

��A few hours to a few days

A few hours to a few days

��Mt. Vesuvius

Mt. Vesuvius

Mt. St. Helens

Mt. St. Helens

Mt.

Mt. Pinotubo

Pinotubo

Plinian

PlinianAnimations

Animations

��http://

http://www.sci.sdsu.edu

www.sci.sdsu.edu/volcano/

/volcano/

��http://

http://www.sci.sdsu.edu/volcano/fly

www.sci.sdsu.edu/volcano/fly

by.m

ov

by.m

ov



��10 feet of ash fell on

10 feet of ash fell on

Pompeii

Pompeii

••Winds m

ust have been

Winds m

ust have been

blowing southward

blowing southward

during the eruption

during the eruption

��38% of the 1,150 bodies

38% of the 1,150 bodies

recovered in Pompeii lie

recovered in Pompeii lie

within the ash fall

within the ash fall

••Mostly crushed under

Mostly crushed under

collapsing roofs

collapsing roofs

••Weight of pumice ash

Weight of pumice ash

has been estimated at

has been estimated at

476 lb/ft

476 lb/ft22

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Volcanic Strata at Pompeii

Volcanic Strata at Pompeii



��Ash fall was followed by a

Ash fall was followed by a

series of

series of pyroclastic

pyroclasticsurges

surges

on the next morning

on the next morning

••Ground

Ground-- hugging, directed

hugging, directed

explosions

explosions

••Super

Super --heated gasses and

heated gasses and

pyroclastic

pyroclasticdebris

debris

••Asphyxiated the remaining

Asphyxiated the remaining

people in Pompeii

people in Pompeii

��62% of the bodies in

62% of the bodies in

Pompeii lie within the

Pompeii lie within the

surge deposits

surge deposits

��Half of these were on the

Half of these were on the

streets and half were

streets and half were

indoors

indoors

Types of

Types of Pyroclastic

PyroclasticFlows

Flows

��Pyroclastic

PyroclasticFlow

Flow: A hot, chaotic avalanche of

: A hot, chaotic avalanche of

pumice, ash, and gasses.

pumice, ash, and gasses. Pyroclastic

Pyroclasticflows can

flows can

move at high speeds along the ground and pass

move at high speeds along the ground and pass

over substantial obstacles. Their distribution is,

over substantial obstacles. Their distribution is,

however, strongly controlled by topography.

however, strongly controlled by topography.

��Pyroclastic

PyroclasticSurge

Surge: A turbulent cloud of volcanic

: A turbulent cloud of volcanic

ash and hot gasses, which hugs the ground and

ash and hot gasses, which hugs the ground and

travels at speeds often exceeding 100 km per

travels at speeds often exceeding 100 km per

hour. Surge deposits are m

ore widely distributed

hour. Surge deposits are m

ore widely distributed

than

than pyroclastic

pyroclasticflow deposits, although not as

flow deposits, although not as

widespread as air

widespread as air--fall pumice layers.

fall pumice layers.

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Types of

Types of Pyroclastic

PyroclasticFlows

Flows

Pyroclastic

PyroclasticFlows at Pompeii

Flows at Pompeii

��The deposits reveal that after the

The deposits reveal that after the Plinean

Plinean

eruption, Pompeii was hit first by a

eruption, Pompeii was hit first by a pyroclastic

pyroclastic

surge

surge, leaving a deposit of 10 to 20 cm, closely

, leaving a deposit of 10 to 20 cm, closely

followed by a

followed by a pyroclastic

pyroclasticflow

flowthat left a deposit

that left a deposit

varying in thickness up to 200 cm

varying in thickness up to 200 cm

��Shortly thereafter, there was a

Shortly thereafter, there was a second

second pyroclastic

pyroclastic

surge

surgeleaving a deposit of 10 to 20 cm, rich in

leaving a deposit of 10 to 20 cm, rich in

fragments of limestone and dense volcanic rocks.

fragments of limestone and dense volcanic rocks.

Pel

Pel ééananEruptions

Eruptions

��Explosive outbursts that

Explosive outbursts that

generate

generate pyroclastic

pyroclasticflows

flows

��Eruption columns are short

Eruption columns are short

��First described from Mt

First described from Mt

Pelee

Peleeon Martinique

on Martinique

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Eruptive History of Vesuvius

Eruptive History of Vesuvius

History of

History of

Vesuvius

Vesuvius

Phlegrean

PhlegreanFields

Fields

��13 km caldera

13 km caldera

��Form

ed 35,000 years

Form

ed 35,000 years

ago

ago

��Eruption of 80km

Eruption of 80km

3

3 of

of

ash

ash

��Two historic eruptions

Two historic eruptions

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Phlegrean

PhlegreanFields Caldera

Fields Caldera

Monte

Monte Nuovo

Nuovo

��Form

ed during an

Form

ed during an

eruption in one

eruption in one

week, beginning on

week, beginning on

September 28,

September 28,

1538

1538

Solfatara

Solfatara

��Volcano form

ed 4000

Volcano form

ed 4000

years ago

years ago

��Last erupted in 1198

Last erupted in 1198

��Boiling m

ud and

Boiling m

ud and

sulfurous vapors

sulfurous vapors

Bradyseism

Bradyseism

��Gradual change in ground elevation due to

Gradual change in ground elevation due to

filling or emptying of a m

agma chamber

filling or emptying of a m

agma chamber

��Between 1968 and 1972, the

Between 1968 and 1972, the Phlegrean

Phlegrean

Fields rose 1.7 m

eters

Fields rose 1.7 m

eters

��Between 1982 and 1984, the

Between 1982 and 1984, the Phlegrean

Phlegrean

Fields rose 1.8 m

eters

Fields rose 1.8 m

eters

��Region still active

Region still active

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Current

Current

Threat?

Threat?

Naples Population

~1 m

illion people

Documents

Eruptions of Mt. Vesuvius Mt Vesuvius and Naplesacademic.brooklyn.cuny.edu/geology/powell/courses... · 79 AD Eruption of Vesuvius August 24 or 25 Explosive eruption that lasted 19