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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)

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volcanic hazards
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
Distribution of active volcanoes

60% around Pacific; 20% in Mediterranean region

  • 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)

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)
classification of volcanic eruptions after scheidegger
Classification of volcanic eruptions (after Scheidegger)

Low RiskHigh RiskGas Pressure


Lava Type


Oceanic ridge,Subduction

Hotspots zone


VEIVolume of tephra Eruption

(m3) type

Eruptionmagnitude= Volcanic Explosivity Index

0 nonexplosive Icelandic/



~106 Strombolian

~107 Vulcanian

~108 Vesuvian

~109 Plinian

~1010 Peléan


~1012 “supereruption”


Types of volcanic hazard


basaltic lava flows
Basaltic lava flows

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

Hazards - property burnt and buried by lava

volcanic hazards 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.

mount vesuvius recent major eruptions
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

Mt. Vesuvius



excavated area of Roman


(20 m below

modern city)

volcanic ash
Volcanic ash

Yakima, WA (May, 1980)

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).



Cleveland Okmok


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

pyroclastic flow nu e ardente
Pyroclastic flow (nuée ardente)

Ruins of St. Pierre, Martinique.

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

Collapse of eruption

column (Mt. MayonPhillipines, 1968)

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.

Volcanic gases

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-eruptiveintense rainstorms (e.g. Hurricane Mitch)
lahars mt rainier
Lahars, Mt Rainier

Osceola lahar:

age: 5600 yrs BPlength: 120 kmvolume: 40x Ruiz

depth: 20mvelocity: >70 km/hpop: 100 000

jokulhlaups e g vatnajokull iceland
Jokulhlaups(e.g. Vatnajokull, Iceland)

In 1996 a subglacial eruption released 4 km3 of meltwater

identification of high risk volcanoes
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

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.

identification of high risk volcanoes 1984
Identification of high-risk volcanoes (1984)

SE Asia and Pacific = 42

Americas and Caribbean = 40

Africa and Europe - 7

Total = 89

(of ~500 active volcanoes)

  • 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)]
  • Omissions (Nevado del Ruiz ~25000 killed in1985!)
Since 1980 some 2M m3 of CO2 released and substantial earthquake activity (some quakes M ~ 6)associated with intrusion of magma tongue

10 km

volcanic hazards in the naples region
Volcanic hazards in the Naples region

Campi Flegrei

La Solfatara




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




Earthquake damage,

Church of Purgatory,



the after effects of a super eruption rampino 2002 icarus v 156 p 562
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)