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Volcanic Hazard Assessment & Mitigationby

Robert P.G.A. Voskuil

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Millions of people live close to dangerous Millions of people live close to dangerous volcanic eruption volcanic eruption centrescentres

Mt. Unzen, Japan

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Many different types of Volcanic HazardsMany different types of Volcanic HazardsLava flowsAsh fallsGlowing cloudsDirect blastsLahars (volcanic debris- and mudflows)Volcanic gasesVolcanic earthquakesTsunami (large sea- or lake waves)Ash clouds endangering aircraft

Hazard assessment, mitigation and zonation: complicated procedure!

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Various types of Various types of volcanic eruption volcanic eruption products cause products cause different types of different types of hazards.hazards.

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Volcanic Hazard AssessmentVolcanic Hazard AssessmentEvaluation 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)Hazard Assessment & Mitigation (1)

Medium- to longterm analysisStudy 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 Analysis of volcanic deposits 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:Analysis of images: LaharLahar flowsflows((Landsat Landsat image,image, KelutKelut volcano, Indonesiavolcano, Indonesia)

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Mapping geomorphology, Mapping geomorphology, Mayon Mayon Volcano, Volcano, PhilippinesPhilippines

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Volcanic Hazard ZoningVolcanic Hazard Zoning

Reconstruction of previous eruptions and quantification of the volume and dispersion of volcanic productsSome very recent eruptions (last 100 years) were studied in detail >> information about the processes responsible for the distribution of the different volcanic products.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: Hazard Zoning: general rulesgeneral rules

The intensity of volcanic phenomena decreases with the distance from the eruptive centre (crater or fissure)Topographic 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 ZoningVolcanic Hazard Zoning

Zoning of each hazard according to:

the frequency of occurrencethe intensity (e.g. the thickness or extent of

the hazard) or 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

Annual frequency : permanent hazard (yearly)Decennial frequency : very high hazard (ten years)Centennial frequency : high hazard (one hundred years)Millennial frequency : low hazard (one thousand years)

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IntensityIntensity, e.g. lava flow extension and thickness of ash deposits

Very high intensity : total destruction of population, settlements and vegetation. High intensity : settlements and buildings partial destroyed

: important danger for the populationModerate intensity : partial damage of structure

: population partly exposedLow intensity : no real danger for population

: damage for agriculture: abrasion, corrosion of machinery,tools, etc.

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Volcanic hazard Volcanic hazard map of map of MerapiMerapi, , Java, IndonesiaJava, 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 Ashfall hazard map Mt. Rainier, USA. hazard map Mt. Rainier, USA. Map includes information on intensity and probabilityMap 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

Volcanic hazard maps are fundamental for volcanic hazard mitigation, but the next step is the preparation of volcanic risk maps

Volcanic risk maps 1. Use data from hazard maps2. Incorporate probability of a volcanic event3. Incorporate economic value and activity4. Incorporate vulnerability to destruction

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(Guatemala)

Landsat TM

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Santa Maria volcano, Guatemala

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Volcanic Risk MapsVolcanic Risk Maps

Volcanic Risk Maps allow for the calculation of the economic impact of an active volcano in ‘dollar’ termsThese 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 & forecastingMonitoring & forecasting

Most volcanic eruptions are preceded by a variety of environmental changes (‘precursory signs’) which accompany the rise of magma towards the surface

1. Seismic activity2. Ground deformation3. Hydro-thermal phenomena4. Chemical changes

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Monitoring & forecastingMonitoring & forecasting

Human surveillance and instrumentalmonitoring of volcanoes (using ground-based& space-based systems) > short term predictions

Techniques:Visual observationsUse of Seismographs (tremors/volcanic earthquakes)Use of tiltmeters and GPS (ground deformation)Measuring gas emission (chemical composition + temperature)Remote Sensing

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Ground based monitoring of volcanic activityGround based monitoring of volcanic activity

Seismograph

Tiltmeter

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Hazard Assessment & Mitigation (3)

Early warning systemsEmergency management and evacuation plansCreating awareness and education programs for people living in volcanic areasLanduse planning, based on hazard zoningBuilding codes (e.g. roof-constructions) Building structures like dikes, to divert lahars

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Use of Remote Sensing & GISUse of Remote Sensing & GIS

Examples :Mapping volcanic terrainHazard & risk zonationMonitoring volcanic activity Monitoring volcanic eruptionsPart of early warning systemsQuantifying volcanic deposits, upstream & downstream (Pinatubo)Damage Assessment after eruptionLand use planning

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Mapping volcanic geology and Mapping volcanic geology and geomorphology:geomorphology: GalunggungGalunggung, Indonesia, 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, 28/7/82Noaa-7,AVHRRColour indicates temperature of plume

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Eruption monitoring (Pinatubo, 1991) (MOS-1)

25 - 11- 1989 5 - 7 - 1991

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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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14/4/94 5/10/94

Mt. Pinatubo, Philippines

SIR-C/X-SAR

Lahar monitoring

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Damage Assessment with sequential aerial Damage Assessment with sequential aerial photographs photographs ArmeroArmero (Colombia): (Colombia):

pre & post eruption of 13 pre & post eruption of 13 november november 19851985

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Damage assessmentDamage assessment, , small format aerial small format aerial

photography, photography, ArmeroArmero, Colombia, Colombia

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Combining imagery with DEMSCombining imagery with DEMS

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Lahar Lahar Hazard Assessment Hazard Assessment Mt.Mt. PinatuboPinatubo

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ModellingModelling erosion at Mt.erosion at Mt. PinatuboPinatubo

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ModellingModelling erosion at Mt.erosion at Mt. PinatuboPinatubo

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Mitigation: Event Modification AdjustmentsMitigation: Event Modification Adjustments

Statements: There is no method to prevent volcanic eruptions There is no defence against threat from pyroclastic flowsLittle can be done to protect crops and exposed water against air-fall tephra

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Environmental ControlEnvironmental ControlLava flows are the volcanic hazard over which mostpysical 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 ControlEnvironmental Control 22

Building barriers to divert lahar flows

Merapi, Indonesia

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Environmental Control 3Environmental Control 3Lower levels of crater lakes to reduce the formation of lahars (Kelut)

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HazardHazard--resistant designresistant designHeavy ash falls:

houses and buildings might collapse under the weight of the ash. Flat roofs should not be used.

Pinatubo ashfall