Volcanic hazard assessment

Volcanic Hazard
Assessment & Mitigation
by
Robert P.G.A. Voskuil
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Millions of people live close to dangerous
volcanic eruption centres
Mt. Unzen,
Japan
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Many different types of Volcanic Hazards
z Lava flows
z Ash falls
z Glowing clouds
z Direct blasts
z Lahars (volcanic debris- and mudflows)
z Volcanic gases
z Volcanic earthquakes
z Tsunami (large sea- or lake waves)
z Ash clouds endangering aircraft
Hazard assessment, mitigation and zonation:
complicated procedure!
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Various types of
volcanic eruption
products cause
different types of
hazards.
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Volcanic Hazard Assessment
z Evaluation of volcanic hazards:
two main complementary approaches, which may lead
to their prediction:
1. Medium- to long term analysis : study of the
eruption history of the volcano, volcanic hazard
mapping, and modelling.
2. Short term : human surveillance and instrumental
monitoring of the volcano (precursory phenomena).
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Hazard Assessment & Mitigation (1)
z Medium- to longterm analysis
ΠStudy of the eruption history of a volcano:
mapping volcanic deposits and assessing
explosivity (VEI), intensity, magnitude and
duration of previous volcanic events >>>>
characterization of overall activity of a
volcano and its potential danger.
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Analysis of volcanic
deposits
Ash fall deposits
Pyroclastic Flow deposits
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Lahar deposits,
not well sorted
(Agung volcano,
Indonesia)
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Analysis of
images:
regional
setting of
volcanoes
Virunga volcanic
chain,Rwanda,
Zaire, Uganda
False colour
composite
Sir-C/X-SAR
3/10/94,
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Analysis of images: Lahar flows
(Landsat image, Kelut volcano, Indonesia)
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0
Mapping geomorphology, Mayon Volcano,
Philippines
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Volcanic Hazard Zoning
z Reconstruction of previous eruptions and
quantification of the volume and dispersion of volcanic
products
z Some very recent eruptions (last 100 years) were
studied in detail >> information about the processes
responsible for the distribution of the different
volcanic products.
z This also resulted in the development of models of
hazardous processes
This information may serve a the base for volcanic
hazard zoning
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Lahar models
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Hazard Zoning: general rules
ΠThe intensity of volcanic phenomena
decreases with the distance from the eruptive
centre (crater or fissure)
ΠTopographic or meteorological factors may
modify the progression of the phenomenon,
such as the diversion of flows by the
morphology.
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Volcanic Hazard Zoning
z Zoning of each hazard according to:
Πthe frequency of occurrence
Πthe intensity (e.g. the thickness or extent of
the hazard)
Πor their combination
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Dating of volcanic eruption products by using
archaeological evidence
Temple complex
covered with 8
meters of
pyroclastic flow
and airfall
deposits
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Frequency scale
z Annual frequency : permanent hazard (yearly)
z Decennial frequency : very high hazard (ten years)
z Centennial frequency : high hazard (one hundred
years)
z Millennial frequency : low hazard (one thousand years)
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Intensity,
e.g. lava flow extension and thickness of ash deposits
z Very high intensity : total destruction of population,
settlements and vegetation.
z High intensity : settlements and buildings partial
destroyed
: important danger for the population
z Moderate intensity : partial damage of structure
: population partly exposed
z Low intensity : no real danger for population
: damage for agriculture
: abrasion, corrosion of machinery,
tools, etc.
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Volcanic hazard
map of Merapi,
Java, Indonesia
Simple map for
public use
No information
on probability of
events
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Map of a
single hazard:
lahar
distribution
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Lahar Hazard,
Mt. Rainier,
USA
Map includes information
on intensity and
probability
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Ashfall hazard map Mt. Rainier, USA.
Map includes information on intensity and probability
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Hazard map of Hawaii:
5 volcanoes and their rift zones
Relative hazard from lava flows
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Multi-hazard
map
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Hazard - vulnerablity - risk
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Volcanic hazard maps are fundamental for volcanic
hazard mitigation, but the next step is the
preparation of volcanic risk maps
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Volcanic risk maps
Use data from hazard maps
Incorporate probability of a volcanic event
Incorporate economic value and activity
Incorporate vulnerability to destruction
1.
2.
3.
4.
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(Guatemala)
Landsat TM
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Santa Maria
volcano,
Guatemala
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Volcanic Risk Maps
z Volcanic Risk Maps allow for the calculation of the
economic impact of an active volcano in ‘dollar’ terms
z These maps are useful for disaster preparedness
planning, because the real cost of the impact of a
volcanic eruption can be compared with costs of
mitigation and monitoring effects.
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Monitoring & forecasting
z
1.
2.
3.
4.
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Most volcanic eruptions are preceded by a variety of
environmental changes (‘precursory signs’) which
accompany the rise of magma towards the surface
Seismic activity
Ground deformation
Hydro-thermal phenomena
Chemical changes
Monitoring & forecasting
Human surveillance and instrumental
monitoring of volcanoes (using ground-based
& space-based systems) > short term predictions
Techniques:
Œ
Œ
Œ
Œ
Œ
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Visual observations
Use of Seismographs (tremors/volcanic earthquakes)
Use of tiltmeters and GPS (ground deformation)
Measuring gas emission (chemical composition +
temperature)
Remote Sensing
Ground based monitoring of volcanic activity
Seismograph
Tiltmeter
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Hazard Assessment & Mitigation (3)
z Early warning systems
z Emergency management and evacuation plans
z Creating awareness and education programs for
people living in volcanic areas
z Landuse planning, based on hazard zoning
z Building codes (e.g. roof-constructions)
z Building structures like dikes, to divert lahars
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Use of Remote Sensing & GIS
Examples :
z Mapping volcanic terrain
z Hazard & risk zonation
z Monitoring volcanic activity
z Monitoring volcanic eruptions
z Part of early warning systems
z Quantifying volcanic deposits, upstream &
downstream (Pinatubo)
z Damage Assessment after eruption
z Land use planning
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Mapping volcanic geology and
geomorphology: Galunggung, Indonesia
Landsat TM
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Monitoring Volcanic activity
Volcanic hot spot at summit of Shishaldin Volcano
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Eruption Monitoring, Mt. Pinatubo, 15 June 1991
13.31 hrs.
14.31 hrs.
15.31 hrs.
GMS visible Images (0.5-0.75 micrometers
wavelength), 1.25 km spatial resolution.
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Monitoring eruption plumes
Galunggung,
Java, 28/7/82
Noaa-7,
AVHRR
Colour
indicates
temperature of
plume
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Eruption monitoring
(Pinatubo, 1991) (MOS-1)
25 - 11- 1989
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5 - 7 - 1991
Pinatubo ash:
global distribution
Eruption June 1991
NOAA AVHRR
images, May 1991,
July 1991, August
1991
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Mt. Pinatubo,
Philippines, 13/4/94
SIR-C/X-SAR,
false colour
Orange:
pyroclastic flow
deposits (1991)
Black:
smooth lahars
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Mt. Pinatubo,
Philippines
SIR-C/X-SAR
Lahar
monitoring
14/4/94
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5/10/94
Damage Assessment with sequential aerial
photographs Armero (Colombia):
pre & post eruption of 13 november 1985
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Damage assessment,
small format aerial
photography,
Armero, Colombia
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Combining imagery with DEMS
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Lahar Hazard Assessment
Mt. Pinatubo
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Modelling erosion at Mt. Pinatubo
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Modelling erosion at Mt. Pinatubo
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Mitigation: Event Modification Adjustments
Statements:
z There is no method to prevent volcanic eruptions
z There is no defence against threat from pyroclastic
flows
z Little can be done to protect crops and exposed water
against air-fall tephra
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Environmental Control
z Lava flows are the volcanic hazard over which most
pysical control can be exerted: diverting and
controlling lava flows by:
1. Bombing or the use of explosives (Etna, Hawai)
2. Artificial barriers (Hawai, Iceland)
3. Water Spray (Hawai, Iceland)
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Environmental Control 2
z Building barriers to divert lahar flows
Merapi,
Indonesia
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Environmental Control 3
z Lower levels of crater lakes to reduce the formation of
lahars (Kelut)
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Hazard-resistant design
z Heavy ash falls:
houses and buildings might collapse under the weight
of the ash. Flat roofs should not be used.
Pinatubo ashfall
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