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Volcanic hazardsMore on monitoring,prediction

and mitigation

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Structure of talk

Monitoring methods seismic and ground deformation other methods

Eruption prediction Hazard mapping Risk awareness and education Case studies

Nevado del Ruiz (1985) Pinatubo (1991) Rabaul (1994)

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Reducing volcanic risk

Return period analysis and risk estimation

Volcano monitoring Eruption forecasting Hazard mapping Intervention Building construction Education and awareness

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Volcano monitoring methods Core methods

Seismic Ground deformation

Supportive methods Microgravity,

electrical & magnetic studies

Geochemical monitoring (gas and water)

Satellite-based methods Global Positioning

System Radar interferometry Thermal monitoring

Monitoring dress code

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Seismic monitoring Vital tool for monitoring

and prediction Baseline monitoring

essential Ideal seismic networks

6 or more local seismic stations (within 15km)

several regional stations (>15km)

capable of detecting volcanic quakes of M 0 beneath volcano

Montserrat 1996

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Seismic monitoring & successes

Earliest volcano observations using seismometers

Vesuvius 1856 Usu 1910 Kilauea 1912 Sakurajima 1914 Aso 1930 Merapi 1924

Over 25 successful forecasts in 20 years

MSH 1980-86 Galeras 1989 Unzen 1990-91 Pinatubo 1991 Mayon 1993 Rabaul 1994 Popocatepetl 1994 Montserrat 1995-7

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Volcano seismicity Five main types of

seismic event: high frequency

(tectonic) low frequency tremor explosion surface (rock falls,

lahars)

Pre-eruption quakes typically swarms M < 5 increase in number occur close to

eruption location

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Pre-eruption swarm sequence

Background

Swarms of high-frequencyevents

Relative quiescenceafter a peak rate

Low frequencyevents

Tremor

Eruption

Deep post-eruptionearthquakes

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Example: Mount St. Helens

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Mount Hood: baseline seismicity

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RSAM method

Real-time Seismic Amplitude Measurement rapid automatic quantitative assessment

methods RSAM provides consecutive 1 or 10m

averages of absolute amplitude or energy for each seismic station regardless of event type

digital recording methods so overcome problem of analogue recorders (drums) becoming saturated

RSAM helped predict eruptions at Pinatubo & Mount St Helens

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RSAM record: Redoubt (Alaska)

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Volcano deformation: principles & methods

Tilt measurement tiltmeter ‘dry’ tilt

Lateral displacements EDM (infrared;

laser;microwave) GPS

Vertical displacements precise levelling

Space-based Radar interferometry laser altimetry

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Ground deformation sources and patterns

Inflation-deflation of magma reservoirIntrusion of dyke, sill or cryptodomeSubsidence due to lava loadingEdifice spreading/sliding under gravity

‘Mogi’ spherical source

Δh

Δh

Linear source(dyke)

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Tilt measurement

Early versions water-tube tilt-meters

‘Dry’ tilt levelling Borehole tiltmeters

provide continuous record

need to be insulated from T and rainfall effects

Problems site specific no measure of

absolute altitude change or horizontal movements

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Tilt related to Pu’u’ ‘O’o eruptions (Kilauea, Hawaii)

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Tilt at Mount St Helens dome 1982

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Precise levelling

Most accurate way of deriving relative height changes

First used to investigate 1910 Usu (Japan) eruption

Regular monitoring tool since mid 1960s

Involves use of a level and graduated measuring staff

time consuming and labour intensive

accuracies of 0.8mm over 1km possible Etna (1989 eruption)

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Precise levelling: the method

Benchmark

Turning point

Benchmark

backsight

foresight

a bc

de

a + e = permanent benchmarksb + c + d = temporary staff and instrument positionsHeight difference e - a = sum of all the foresights minussum of all the backsights

Any number of turning points may be used

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Electronic distance measurement Measures horizontal

distance changes in a network of benchmarks

Uses laser or IR Total Stations (incorporate electronic theodolite)

Light beam bounced off reflector a few kms away

Preliminary distance read from instrument

Corrections for T and P made to give final distance

accuracies of a few cm

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Global Positioning System Most accurate way of

measuring horizontal position over large distances

Utilises ‘constellation’ of ~ 24 satellites that beam radio signals to Earth

Determines precise distance to satellite and thus position on Earth

At least four satellites needed

Accuracies of a few mm over 10s km using dual receiver differential GPS

drawbacks: line of sight; weatherEtna 1996

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GPS: the method

One antenna (rover) is set up vertically above a benchmark

Locked on to satellites ~ 15 minutes. Data stored in hand-held controller

A second antenna (base) is left locked on to satellites at start of day’s work

Rover moved on to successive benchmarks in a network designed to provide good spatial coverage

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Integrated monitoring networks

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Microgravity monitoring Measures small changes

in value of g at a network of stations

Changes in Earth’s gravity field measured in µGals

On volcanoes changes in sub-surface M and D results in Δg of 10s - 100s µGals

Changes due to variety of processes including intrusion & vesiculation

Interpretation of data not straightforward

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Microgravity data interpretation

Microgravity readings must be taken in tandem with elevation change readings (levelling or GPS)

If Δg are due solely to Δh, readings should plot on a straight line known as the Free Air Gradient

If data plot off this line, an explanation in terms of sub-surface mass change must be sought volcanic processes or water table changes?

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Interpreting micro-gravity changes on volcanoes

Height decrease-Δh(m)

Height increaseΔh(m)

Gravity increase Δg(μGal)

Gravity decrease -Δg(μGal)Free airgradient

Mass Mass

Magmavesiculationor drainage,creation of voidsor fall in watertable

Magmaintrusion,devesiculationor void fillingor rise in water table

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Synthetic Aperture Radar (SAR)

Two satellite images taken on different orbits from almost same point in space superimposed

Phase differences between images produces interferometric fringes

Allow detection of surface changes between images

No ground instrumentation needed

Accurate to ~ 3cmMount Etna 1991 - 93

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Satellite SAR interferometry

Mount Etnapost 91-93eruption

Contractionof sphericalmagmareservoir

Still some problems• atmospheric• snow cover/vegetation• high relief

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Gas monitoringCOSPEC

TOMSDirectsampling

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Satellite thermal monitoring

Pavlof volcano, Alaska

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Predicting volcanic eruptions

Pre

curs

ory

dat

aTime

E.g. tiltseismic energyreleaseSO2 emission

Primarily based upon detecting accelerations in pre-cursory activity

Allow definition of successively narrower predictive windows

Can be linked to warnings and alert level system

Terminology crucial factual statements predictions

Not fool proof MSH collapse

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Hazard zonation Predict future hazards on

basis of past activity Can be constructed for

single or all hazards Dependent on

representative preservation

Require detailed geological mapping, dating and correlation

Aided by computer simulations

Boundaries must be regarded as approximate and conservative

Lava flow hazardHawaii

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The ideal Hazard Zonation map

Mount St. Helens 1980 eruption deposits

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Single hazard zonation map: lahars at Mount Rainier

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Composite hazard zonation map

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Risk awareness and education

Critical role in reducing impact of volcanic eruptions

Progressive programme raising awareness of

the threat educating about the

nature of the threat training in

preparedness and crisis response

Culmination successful handling

of volcanic event

Auckland newspaper cartoon after Rabaul(PNG) 1994 eruption

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Risk education

Active caldera (Azores)

Overcoming the ‘not in my lifetime’ problem

Coherent public education programme critical

multiple messages multiple channels multiple agencies consistent message

Schools play a vital role People respond to

personalized information facts about likelihood &

severity practical precautionary

measures

Involvement (Philippines)

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Emergency response

Effective emergency response depends upon

pre-crisis education and training

an established information and warning system

a simple and understandable ALERT SYSTEM

Successes Pinatubo (1991) Rabaul (1994)

Failure: Ruiz (1985)

Pinatubo (1991)

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Pinatubo 1991

Last eruption ~600y previous 3 month build-up to climax Combined response by

PHIVOLCS & USGS Rapid monitoring set-up Alert system established

over a month before climax Rapid hazard mapping of PF

deposits undertaken Video used in public

awareness programme 200,000 evacuated in

advance (progressive) Potential death toll ~15,000;

actual ~500

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Nevado del Ruiz (1985) Small eruption - 1/10 size of

Mount St. Helens Armero - 72km from summit Hazard mapping indicated

risk from lahars due to PF triggered snow melt

Police informed after eruption began: no action

Emergency Management Plan due for review 2 days later

No preparedness No alert system or

evacuation procedure No precursive signs Death toll ~ 23,000

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Rabaul 1994 Seismic crisis from 1983 -

1985 Triggered programme of

public education, establishment of alert system and evacuation exercises

Quiescent for 9 years Eruption in September

1994 following just 27 hours of intense seismicity and surface deformation

Populace self-evacuated death toll ~5

Current monitoringsituation

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Rainier& Hood

MammothLakes

Michoacanvolcanic field

Dominicaand others

Vesuvius& Campi Flegrei

Aucklandvolcanic field

The future: some possible volcanic gaps

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