Volcanic hazards• >1300 volcanoes known to

have erupted in Holocene (last 10 000 years)

• ~500 classified as ‘active’ (i.e. known to have erupted in recorded history)

• Remainder classified as ‘dormant’ (may become active again) or ‘extinct’ (not expected to erupt again), but Vesuvius was thought to be extinct before AD 79!

Plus new vents: e.g. Paricutin (Michoacan,

Mexico)shown erupting in 1943

(graphic by Diego Rivera)

Distribution of active volcanoes

60% around Pacific; 20% in Mediterranean region

Major volcanic eruptions since AD1600 (>8000 deaths)

Event Date Deaths Hazard type

Laki, Iceland 1783 9000 Starvation

Unzen, Japan 1792 14300 70% by cone collapse;30% by tsunami

Tambora, Indonesia 1815 92000 90% by starvation

Krakatoa, Indonesia 1883 36000 90% by starvation;<10% pyro. flows and tephra

Mt. Pelée, Martinique 1902 29000 Pyroclastic flows

Nevada del Ruiz,Colombia

1985 25000 Lahars

Volcanoes

Eruptive style and hazard depends on:

•Tectonic setting

•Depth of magma formation

•Rate of magma movement to the surface

•Percent and type of volatiles (gases)

Volcanoes - tectonic settings

examples?

Oceanic ridge, SubductionHotspots zone

Basic/Mafic volcanics

•Low SiO2

•Fluid lava (10 m/s)

•Low gas pressure(little explosive activity)

Acidic/Felsic volcanics

•High SiO2

•Viscous lava (3 m/s)

•High gas pressure(explosive activity)

Low Medium High

Fluid Icel andicHaw aii an

Stro mbol ia n Vesuvi an

Inter. - Vulc anian Perr et ian

Viscous Mer apian Vin centi an Pel éean

Classification of volcanic eruptions (after Scheidegger)

Low Risk High Risk Gas Pressure

Low

High

Lava

Typ

e

Oceanic ridge, SubductionHotspots zone

Eruptionmagnitude

= Volcanic

Explosivity Index

VEI Volume of tephra Eruption (m3) type

0 nonexplosiveIcelandic/

Hawaiian1 <105

2 ~106 Strombolian3 ~107 Vulcanian4 ~108 Vesuvian5 ~109 Plinian6 ~1010 Peléan7 ~1011 8 ~1012

“supereruption”

Types of volcanic

hazard

http://volcanoes.usgs.gov/Hazards/What/hazards.html

Volcanic hazards:deaths (AD 1900-2000)

Pyro flowsLaharsDisease, etc.Tephra fallsOthersUnknown

Basaltic lava flows

Hazards - property burnt and buried by lava

“Aa” (blocky lava) flow, Hawai “Pahoehoe” (ropy lava) flow, Reunion

Recent major lava

flows, Hawai’i

Volcanic hazards - Hawai’i

Five active volcanoes;hazards are mainly lava flows, although tephra and gas emissions also occur. Hazard profile similar for all three.

IberianAfricanApulianEurasianEurasian

IranianIo.VolcanoesPlate motions

Volcanoes of the Mediterranean

Mount Vesuvius: recent major eruptions

• A.D. 79: destruction of Pompeii and Herculaneum;

• 80 eruptions since then -most violently in 1631 and 1906; quiet since 1944

Eruption of Vesuvius, A.D. 79

08060402002220181412

756432

711m

Volcanic deposits756432

1

from Pliny’s letters

Pumice begins to fall on Pompeii

First surge cloud kills Herculaneumvictims; pyroclastic flow followsSecond surge and flowThird surge reaches northern walls ofPompeii; flow buries HerculaneumFourth surge asphyxiates Pompeii victims;flow followsFifth surge and flowSixth (final) surge causes Pliny to fleeMisenum; flow buries Pompeii

Mt. Vesuvius

modern Herculaneum

excavated area of Roman

Herculaneum(20 m belowmodern city)

Volcanic ash

Fine-grained volcanic ash can cause health problems in susceptible people, clog ventilation systems, cause electrical short circuits, damage crops, and wreck jet engines (e.g. the BA 747 that lost all 4 engines and dropped 4 km after encountering an ash cloud over Indonesia in 1982).

Yakima, WA (May, 1980)

Spurr

KasatochiCleveland Okmok

Visit the AVO website [http://puff.images.alaska.edu/] for animations of current eruptions

Ash cloud from the eruption of Mt. Spurr (Alaska) in 1992

Dominant wind directions,Mt. Baker

Pyroclastic flow (nuée ardente)

Collapse of eruptioncolumn (Mt. MayonPhillipines, 1968)

Ruins of St. Pierre, Martinique.Pyroclastic flow (>700°C; ~200 km/h) from Mt. Pelée in 1902 killed 30 000 people; 2 survived.

Volcanic gases

Lake Nyos (Cameroon, 1986).More than 1700 people killed as a result of a massive release of CO2; formed a ‘river’ about 50m deep that flowed for 25 km. L. Nyos currently contains about 350 M m3 of CO2. Similar event at L. Monoun (Cameroon) in 1984 resulted in 37 deaths.

In 1783 a massive fissure eruption near Laki, Iceland released huge amounts of basaltic lava (5 000 m3/s), and a ‘dry fog’ rich in SO2 and flourine. Some 75% of stock animals in Iceland died, the subsequent famine killed 10 000 people.

Lahars: volcanic mudflows

•Eruptive “volcanic rain” (e.g. Herculaneum) melting of summit snow/ice (e.g. Nevado del Ruiz)

•Post-eruptive intense rainstorms (e.g. Hurricane Mitch)

Lahar resulting

from volcanic rain

Nevado del Ruiz, Colombia

Lahars, Mt Rainier

Osceola lahar:age: 5600 yrs BP

length: 120 kmvolume: 40x Ruiz

depth: 20mvelocity: >70 km/h

pop: 100 000

Jokulhlaups (e.g. Vatnajokull, Iceland)

In 1996 a subglacial eruption released 4 km3 of meltwater

Identification of high-risk volcanoes

• Frequency and nature of past eruptions

• Distribution and nature of eruptive products

• Population density and property value in vicinity of volcano

BedDate (BP)

Eruptive styleVolume (km3)

Pompeii

~1900 Plinian 2.8

AP6 ~2200 Strombolian ?

AP5 ?Strombolian to Vulcanian

0.08

AP4 ? Phreato-Plinian 0.12

AP3 ~2700Strombolian to Vulcanian

0.15

AP2 ~3000Sub-Plinian to phreato-Plinian

0.14

AP1 ~3300Sub-Plinian to phreato-Plinian

0.15

Avellino

~3450 Plinian 1.5

Why wasn’t Vesuvius recognized as high-risk by the Romans?

From data in: Andronico, D. and Cioni, R. 2002. Bull. Volcanology 64, 372-391.

Caveat: “low ratings may simply reflect incomplete or incorrect information, not necessarily low risk. In fact, volcanoes not listed should be the focus of... investigation” [Yokohama et al. (1984)]

Identification of high-risk volcanoes (1984)

SE Asia and Pacific = 42Americas and Caribbean = 40 Africa and Europe - 7

Total = 89 (of ~500 active

volcanoes)

Omissions (Nevado del Ruiz ~25000 killed in1985!)

Monitoring techniques

Gas sampling at vents (craters, fumaroles)

Monitoring and

prediction

(Mt St Helens, 1982)

“Super-volcanoes”

Continental caldera formation

Since 1980 some 2M m3 of CO2 released and substantial earthquake activity (some quakes M ~

6) associated with intrusion of magma tongue

10 km

The last super-eruption from Long Valley caldera

Bishop Tuff

Volcanic hazards in the Naples region

Campi Flegrei

La Solfatara

Tectonic deformation, Campi Flegrei

(1982-1985 pulse)

Ruins of Roman market, Pozzuoli; inundated by sea,

uplifted by 2m in <10 years as a result of

volcano-tectonic forces beneath Campi Flegrei

caldera

1976

1984

Earthquake damage,Church of Purgatory,

Puzzuoli1982

La Solfatara, one of several small active craters in the Campi Flegrei

City of Naples

The after-effects of a super-eruption(Rampino, 2002, Icarus, v.156, p. 562)

Stratospheric loading of ~1000 Mt of SO2 and sulphate aerosols

Aerosol veil persists for 5 - 10 years Global cooling of 3-5°C (locally 15°C) Collapse of agricultural production for several

years --> famine --> conflict Last great supereruption (Toba, ~73,000 BP)

may have reduced human population to ~10,000 people (Ambrose, 1998, J. Human Evolution., v. 34, 623)