Volcanic hazards
description
Transcript of 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
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
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Volcanic deposits756432
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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)