Transcript Document

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
Unzen, Japan 1792
Tambora, Indonesia 1815
Krakatoa, Indonesia 1883
Mt. PelЋe,Martinique 1902
Nevada del Ruiz, 1985
Colombia
9000 Starvation
14300 70% by cone collapse;
30% by tsunami
92000 90% by starvation
36000 90% by starvation;
<10% pyro. flows and tephra
29000 Pyroclastic flows
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,
Hotspots
Subduction
zone
Basic/Mafic volcanics
Acidic/Felsic volcanics
•Low SiO2
•High SiO2
•Fluid lava (10 m/s)
•Viscous lava (3 m/s)
•Low gas pressure
(little explosive activity)
•High gas pressure
(explosive activity)
Classification of volcanic eruptions
(after Scheidegger)
Low
High
Lava Type
Low Risk
Fluid
Inter.
High Risk
Gas Pressure
Low
Medium
High
Ic e l a n d ic
Haw a ii an
-
St ro mb o l ia n
Vesu vi an
Vulc a n ia n
P err e t ia n
Vin c en ti an
P e l ée an
Viscous Mer a p ia n
Oceanic ridge,
Hotspots
Subduction
zone
Eruption
magnitude
=
Volcanic
Explosivity
Index
VEI
Volume of tephra Eruption
(m3)
type
0
nonexplosive
1
2
3
4
5
6
7
8
<105
~106
~107
~108
~109
~1010
~1011
~1012
Icelandic/
Hawaiian
Strombolian
Vulcanian
Vesuvian
Plinian
Peléan
“supereruption”
Types of
volcanic
hazard
http://volcanoes.usgs.gov/Hazards/What/hazards.html
Volcanic hazards:
deaths (AD 1900-2000)
Pyro flows
Lahars
Disease, etc.
Tephra falls
Others
Unknown
Basaltic lava flows
“Aa” (blocky lava) flow, Hawai
“Pahoehoe” (ropy lava) flow, Reunion
Hazards - property burnt and buried by lava
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.
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
Mt. Vesuvius
modern
Herculaneum
excavated area
of Roman
Herculaneum
(20 m below
modern city)
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).
Spurr
Cleveland Okmok
Kasatochi
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 eruption
column (Mt. Mayon
Phillipines, 1968)
Ruins of St. Pierre, Martinique.
Pyroclastic flow (>700°C; ~200 km/h)
from Mt. Pelée in 1902 killed 30 000
people; 2 survived.
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-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 km
volume: 40x Ruiz
depth: 20m
velocity: >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
Why wasn’t Vesuvius recognized as high-risk by the Romans?
Bed
Volume (km3)
Date (BP) Eruptive style
Pompei
i
~1900
Plinian
AP6
~2200
Strombolian
AP5
?
Strombolian to
Vulcanian
0.08
AP4
?
Phreato-Plinian
0.12
AP3
~2700
Strombolian to
Vulcanian
0.15
AP2
~3000
Sub-Plinian to phreatoPlinian
0.14
AP1
~3300
Sub-Plinian to phreatoPlinian
0.15
From data in: Andronico, D. and Cioni, R. 2002.
Avellin
~3450
Plinian
o
2.8
?
Bull. Volcanology 64, 372-391.
1.5
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)
 Omissions (Nevado del Ruiz ~25000 killed
in1985!)
 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)]
Monitoring techniques
Gas sampling at vents
(craters, fumaroles)
Monitoring
and
prediction
(Mt St
Helens, 1982)
“Super-volcanoes”
10 km
Since 1980 some 2M m3 of CO2 released and
substantial earthquake activity (some quakes M ~ 6)
associated with intrusion of magma tongue
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,
Puzzuoli
1982
City of Naples
La Solfatara, one of several small active craters in
the Campi Flegrei
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)