Monitoring Volcanoes & Predicting Eruptions monitoring.pdf · Seismic Analysis Centre in the...

Monitoring Volcanoes

& Predicting Eruptions

I.G Kenyon

Why Monitor?

At least 200,000

people killed

by volcanoes over

the last 500 years

Why Monitor?

500 active volcanoes on land

10% of world population live

on their flanks (640 million)

Major

Eruptions

In the last

2000 years

Earthquakes

kill far more

people than

volcanoes

1815, 1883

1902, 1985

Monitoring – USA - Where?

Hawaiian Volcano Observatory

(HVO)

Cascades Volcano Observatory

(CVO)

Alaskan Volcano Observatory

(AVO)

Monitoring – Where?

Italy

Japan

New Zealand

The Philippines

Russia

Most active volcanoes are not monitored

Monitoring Techniques

Volcanocams

Seismic studies

Gas Analyses

Ground Deformation

Gravity Surveys

Hydrological Surveys

Electrical/Magnetic

Surveys

Monitoring Sakurajima, Japan

Monitoring Techniques - Volcanocams

On Stromboli in the Aeolian

Islands a surveillance

camera has been installed

on the peak of the volcano

The camera transmits

‘real-time’ images of

the volcano’s activity 24

hours a day to a monitoring

centre in Catania where

the pictures are analyzed

Volcanic Seismic Activity

Seismic Analysis Centre in the Vesuvian observatory in Naples, Italy

Transmission stations that collect seismic data have

been set up on Vesuvius, Campi Flegrei and the island

of Ischia and the collected information is studied here

Volcanic Seismicity 3 major types of seismic information

Short-period earthquakes are like normal

fault related earthquakes. They are caused

by magma forcing its way upwards and

fracturing brittle rock in the process.

Long-period earthquakes indicate increased

gas pressure in the volcano’s plumbing system.

Analagous to the clanging sometimes

heard in your home’s plumbing system.

Harmonic tremor occurs due to sustained movement

of magma below the surface often as it is vibrating

or pulsating within the feeder pipe or conduit.

Volcanic Seismic Activity

Prior to eruptions, many earthquakes

occur which get progressively shallower

Earthquakes are caused by magma forcing

its way towards the surface and fracturing the

surrounding rock as it migrates upwards

Some earthquakes are due to ‘harmonic tremor’

where the magma is vibrating within the conduit

Volcanic Seismic Activity

In addition to monitoring actual seismic activity around

volcanoes, artificial events using explosives are employed

to build up a 3 dimensional picture of the structure and

plumbing of the magmatic system within the volcano

Portable seismometer

for registering earth

tremors in the field

Seismic tomography has

been used on Vesuvius

for the last decade

Major Gases given off by Volcanoes

Over 80% is

water vapour

Carbon Dioxide, Sulphur Dioxide, Hydrogen, Hydrogen Sulphide

and Hydrogen Chloride make up the bulk of the remainder

Gas Emissions

Fully automatic

gas sampling

equipment set

up in a fumarolic

area on the island

of Vulcano, Italy

Total amount of gas released increases

prior to an eruption, the sulphur dioxide

proportion increasing most dramatically

Gas Emissions in Rambleta crater at the summit of Mount Teide, Tenerife

Fumaroles belch out a mixture of water

vapour, carbon dioxide and sulphur dioxide

Acicular (needle-like) crystals of

yellow sulphur and white alunite are

precipitated around the fumaroles

Instruments used to analyse Gas Emissions

COSPEC – Correlation spectrometer to

measure the amount of sulphur dioxide.

These may be mounted on a tripod, on a

vehicle or attached to an aeroplane/helicopter

FLYSPEC – miniature version of COSPEC that

can be attached to a hard hat or back pack

LI-COR – Infra-red analyzer to measure the amount

of carbon dioxide in a volcanic plume

FTIR – Fourier Transform Infrared Spectrometer

continuously samples gas in a volcanic plume

GASPEC – measures carbon

dioxide in a volcanic plume

Monitoring Gas Emissions

COSPEC Correlation Spectrometer

continuously monitors

sulphur dioxide emissions

from active volcanoes

COSPEC Instrument

COSPEC mounted on an aeroplane

COSPEC mounted on a vehicle

Monitoring Ground Deformation

Traditional Methods – surveying

by levelling, theodolite surveying

EDM - Electronic Distance

Measurement using infrared/laser

Tiltmeters – record changes in angle of slope

GPS – Global Positioning Systems

InSAR – Interferometric Synthetic Aperture

Radar using satellite measurements

Measuring EDM distance to Mount St.Helens Lava Dome

A target on the west side of the dome was moving 2cm per day

2 weeks before the May 14th 1982 eruption; movement increased

to about 200cm per day by May 13th. Such accelerations were

frequently used to predict eruptions in 1982

Monitoring Equipment Locations around Mount St.Helens

Measuring Ground Deformation

A B

C

Typical Hawaiian Pattern

A - Volcano begins to inflate

B - Inflation reaches its peak

C - Eruption followed by deflation

Stars show the location

of deep boreholes on

Mauna Loa where new

monitoring equipment

has been installed

Each borehole contains:

An ultra-sensitive

strainmeter

A three-component

broadband seismometer

A strong motion sensor

Tiltmeters may be added

high in each borehole

later this year

Monitoring Mauna Loa and Kilauea, Hawaii

Monitoring Mauna Loa and Kilauea, Hawaii

Cross section showing installation

of a strainmeter and seismic

package on Mauna Loa

The strainmeter is encased

in expansive grout 100-120m

below the surface

The seismometers are

encased in cement 10-20m

above the strainmeter

The strainmeter is installed below

the steel casing as it must be

secured to the surrounding rock

so that it can ‘sense’ the pressure

being exerted on the rock

Strainmeters are also

known as dilatometers

Monitoring Mauna Loa and Kilauea, Hawaii

A strainmeter is a stainless steel pipe 3m long

and 10cm in diameter, filled with silicon fluid

As moving magma or earthquakes cause the ground to

change shape, the dilatometer is squeezed like a balloon

The amount of strain is determined by

measuring the flow of the silicon fluid into or out

of the dilatometer into a secondary reservoir

The instruments are very sensitive and can even

detect small deformations due to passing weather

fronts and the gravitational pull of the sun and the moon,

These changes are filtered out by analysis software, and

what is left is a measure of the deformation of the ground

A three-component broadband seismometer

Horizontal Sensors

Vertical Sensors

The size and

cylindrical shape

of the instrument

are governed by

the shape and

diameter of the

drill hole

These are just

miniature versions

of the seismic

sensors placed at

the earth’s surface

Monitoring Mauna Loa and Kilauea, Hawaii

The DOSECC drilling rig

on the northern flank of

Mauna Loa at 3,350m

elevation. Mauna Kea

rises above the clouds

in the background

Drillers attach a new

length of pipe before

coring another section

of basalt

Monitoring Mauna Loa and Kilauea, Hawaii

The cored rocks are

examined and logged

by scientists from the

Hawaiian Volcano

Observatory (HVO) and

from The Centre for the

Study of Active Volcanoes

(CSAV)

These cores give

scientists a record of

the eruptive history of

Mauna Loa volcano

close to its rift zones

Monitoring Mauna Loa and Kilauea, Hawaii

A solid section of

basaltic rock was

needed to firmly anchor

the strainmeters

After a depth of

90-100m was drilled

the basalt encountered

was homogenous and

had few fractures

Basalt suitable

to house the

strainmeter

Monitoring Mauna Loa and Kilauea, Hawaii

Expansive grout being

poured into the hole after

the strainmeter to anchor

it to the surrounding rock

An array of surface electronics

connect to the instruments in the

borehole. The photo below is a

completed installation at Hokukano

Ranch on the west flank of Mauna Loa

Monitoring Changes in Gravity

Changes in gravity can be

used to estimate subsurface

movements of water or magma

Above-Lacoste & Romberg

micro-gravity meter. The station

consists of a survey pin driven

into the bedrock-in this case

part of a pahoehoe lava flow

Below-gravity record from

Masaya Volcano 1993 - 2000

Hydrological Monitoring

Level and temperature of

groundwater in boreholes

Monitoring of lake levels

Monitoring of stream discharges

Monitoring of water quality

Coldwater Lake Gauging Station

Monitoring of stream

sediment loads

River channel surveys to

measure bank and channel

erosion and channel deposition

at specific locations

Hydrological Monitoring

Overflow channels have been built at Castle

and Coldwater Lake to stabilise water levels

and prevent overtopping of the debris dams

Coldwater Lake

Debris Dam

Overflow Channel

Electrical and Magnetic Surveys

Deviations in local

electrical and magnetic

fields are responses to

pressure and stresses

are caused by the

subterranean

movement of magma.

Mount Etna has 5

automated magnetic

monitoring stations and

data collected has been

used to predict eruptions

from 2001 onwards

Computer Modelling of Volcanic Hazards

Satellite image of the area around Vesuvius with superimposed

isolines to indicate areas where the accumulated ashfall would be

more than enough to cause the collapse of the roofs of homes

90%

80%

70%

Likelihood of roof collapse (%)

Mount Rainier, Cascades, USA

Hazard Zonation Map

Collecting data from

previous eruptions allows a

detailed picture of potential

hazards from future

eruptions to be established

The map shows areas likely to

be at risk from lava flows,

pyroclastic flows and lahars

Contingency plans are

formulated from this data and

may involve evacuation and

protection measures

Mount

Pinatubo

Map to show volcanic

hazards associated

with the 1992 eruption

Depth and distribution

of ashfall, deposits

from pyroclastic flows

and volcanic

mudflows (lahars)

Building in the lower

pats of the valleys

affected by lahars is

now to be restricted

Predicting Eruptions

Building up a detailed knowledge of past eruptions

allows patterns or cycles of activity to be identified.

From this predictions of future eruptions may be made

The End