Monitoring Volcanoes & Predicting Eruptions monitoring.pdf · Seismic Analysis Centre in the...
Transcript of Monitoring Volcanoes & Predicting Eruptions monitoring.pdf · Seismic Analysis Centre in the...
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Monitoring Volcanoes
& Predicting Eruptions
I.G Kenyon
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Why Monitor?
At least 200,000
people killed
by volcanoes over
the last 500 years
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Why Monitor?
500 active volcanoes on land
10% of world population live
on their flanks (640 million)
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Major
Eruptions
In the last
2000 years
Earthquakes
kill far more
people than
volcanoes
1815, 1883
1902, 1985
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Monitoring – USA - Where?
Hawaiian Volcano Observatory
(HVO)
Cascades Volcano Observatory
(CVO)
Alaskan Volcano Observatory
(AVO)
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Monitoring – Where?
Italy
Japan
New Zealand
The Philippines
Russia
Most active volcanoes are not monitored
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Monitoring Techniques
Volcanocams
Seismic studies
Gas Analyses
Ground Deformation
Gravity Surveys
Hydrological Surveys
Electrical/Magnetic
Surveys
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Monitoring Sakurajima, Japan
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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
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Monitoring Equipment Locations around Mount St.Helens
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Measuring Ground Deformation
A B
C
Typical Hawaiian Pattern
A - Volcano begins to inflate
B - Inflation reaches its peak
C - Eruption followed by deflation
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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 (%)
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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
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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
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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
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The End