Etna 2003

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Etna 2003
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Most volcanoes occur in narrow belts or are
grouped together in small clumps. This is because
they usually occur at plate boundaries. One such
belt of volcanoes is called the Ring of Fire,
which runs around the edge of the Pacific Ocean,
where, amongst others, the Pacific Plate meets
the Eurasian Plate, the Indo-Australian Plate,
the Antarctic Plate, and the Nazca
Plate. Forecasting involves probable character
and time of an eruption in a monitored volcano.
The character of an eruption is based on the
prehistoric and historic record of the volcano in
question and its volcanic products. For example,
a violently erupting volcano that has produced
ash fall, ash flow and volcanic mudflows (or
lahars) is likely to do the same in the future.
Determining the timing of an eruption in a
monitored volcano depends on measuring a number
of parameters, including, but not limited to,
seismic activity at the volcano (especially depth
and frequency of volcanic earthquakes), ground
deformations (determined using a tiltmeter and/or
GPS, and satellite interferometry), and gas
emissions (sampling the amount of sulfur dioxide
gas emitted by correlation spectrometer, or
COSPEC  
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Many kinds of volcanic activity can endanger the
lives of people and property both close to and
far away from a volcano. Most of the activity
involves the explosive ejection or flowage of
rock fragments and molten rock in various
combinations of hot or cold, wet or dry, and fast
or slow. Some hazards are more severe than others
depending on the size and extent of the event
taking place and whether people or property are
in the way. And although most volcano hazards are
triggered directly by an eruption, some occur
when a volcano is quiet.
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Anatahan Volcano eruption, May 11, 2003 Northern
Mariana Isles
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Long before the Hawaiian Isles were formed, at
the end of Cretaceous there were massive
volcanism on the Earth. Mass extinction of
dinosaurs is attributed to those changes, at the
Cretaceous-Tertiary Boundary (KT) 65 million
years ago.
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But what will those signals be?
Millions live in the shadows of nature's ticking
time-bombs--volcanos. An apocalyptic volcanic
blast will not come unheralded. No volcano is
going to suddenly produce one of these humongous
eruptions without giving a lot of signals. But
what will those signals be?
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Historic Record of Eruption and Lahar, Japan
About 1-m thick mud including many blocks drapes
the present topography 300-m west of Aramaki
Campus, Gunma University at Maebashi. This
deposit is emplaced by the Kambara hot lahar
originated from the northern flank of Asama on
August 5, 1783. Outcrop exposed by urban
development.
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Mt. Pagan, Northern Mariana, Guam, 1994
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Kilauea, 1996.
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Forecasting a Volcanic Eruption
As the world's population grows, more and more
people are living in potentially dangerous
volcanic areas. Volcanic eruptions continue--as
they have throughout history--posing ever-greater
threats to life and proper There are mainly two
internal heat sources that drive plate tectonics
and volcanic eruptions heat left over from the
formation of the earth, and decay of radioactive
elements within the earth. Volcanic eruptions
account for a large proportion of the internal
heat that is dissipated from the interior of the
earth. Are Volcanic Eruptions Tied to Lunar
Cycle? Gravity is one of Earth's strongest
forces, so you can't ignore the moon. The
challenge is to find out just how it's playing a
role
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Glaciers and Volcanoes Climate and environmental
change can trigger volcanic eruptions. Over the
past 800,000 years, a new study shows, glaciers
prompted eruptions after they retreated north.
One possibility is that all the extra weight of
the glacial ice holds the magma, or molten rock,
in place. Then when the ice melts and the water
evaporates, less weight on the Earth's crust
triggers volcanoes to erupt.
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• Hazardous volcanic activity poses a threat to
  people and property. Unlike most other natural
  hazards, the damage inflicted by volcanoes can be
  significantly mitigated if volcanic behavior is
  assessed rapidly, as dangerous situations
  develop.
• Volcanic Hazards
• Local volcanic hazards The magnitude of the
  proximal threat is much larger. There is the
  potential for many (perhaps thousands) of deaths
  and of extensive or total destruction of
  buildings, roads, dams, pipelines, or any other
  structures in the area. The surface drainage
  pattern may be disrupted, and arable land or
  forest temporarily or permanently destroyed.
• Proximal hazards require evacuation of people,
  livestock, any other movable property, to
  appreciable distances from their homes, for
  uncertain lengths of time, often weeks or months.
  
• 2. Local and Distant Tsunamis in the Coastal and
  Oceanic Volcanic Eruptions
• Atmospheric Disseminated ash-plume, Aviation
  hazard
• Pollution, Vog, Haze, Global cooling

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Scientists monitor temperature changes, volcanic
gases, seismic activity, and apparent "ground
uplifts" in the volcano and nearby fields to
detect warning signs of a coming eruption, The
key thing is to cross-correlate as many different
observations as possible.
Strengths in the event of a volcanic crisis are
(1) familiarity with the eruptive history and
probable behavior of the local volcano(es), (2)
previously established local credibility based on
that knowledge, and (3) established connections
with relevant local government officials and
emergency responders.
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There are two distinct circumstances in which
volcanologists monitor activity at volcanoes (1)
unrest at a volcano that has been dormant, but
which may be preparing to erupt and (2) activity
at a volcano during an eruption, particularly a
long-term eruption with spurts of accelerated
activity or pauses (as at Kilauea, or Etna, or
the slow dome-building eruptions of Montserrat or
Unzen). In the first instance, the volcano will
erupt only if there is renewed influx of magma
from deep within the earth. Magma movement
triggers earthquakes and tremor, hence the
widespread use of seismic networks as the
monitoring method of first resort. Satellite
monitoring can come into play only when the magma
is near enough to the surface to produce surface
deformation, or enhanced heat flow or gas
emissions. At this later stage of reawakening,
volcanologists need all the information they can
get to evaluate the probability of an eruption,
and it is here that remote sensing may usefully
contribute. The best tool for public education
found so far is videos of actual eruptions and
their consequences.
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Precursor phenomena as eruption
forecasters Precursor an event that commonly
precedes another event - we look for events or
phenomena that occur before eruptions and see if
eruptions often occur after certain events or
sequences of events or phenomena Seismic
Signals the hidden signatures that
volcanologists seek in the noise emanating from a
restless volcano are measured on a
seismograph. . Volcano-Tectonic Event Long
Period Event Tremor Hybrid
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A seismograph is a simple pendulum. When the
ground shakes, the base and frame of the
instrument move with it, but intertia keeps the
pendulum bob in place. It will then appear to
move, relative to the shaking ground. As it moves
it records the pendulum displacements as they
change with time, tracing out a record called a
seismogram
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Gas composition monitor the composition of gases
that are continually vented from the volcano, and
note some unique changes in the gas composition
have correlated with eruptions that followed
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Forecasting a Volcanic Eruption
As the world's population grows, more and more
people are living in potentially dangerous
volcanic areas. Volcanic eruptions continue--as
they have throughout history--posing ever-greater
threats to life and proper There are mainly two
internal heat sources that drive plate tectonics
and volcanic eruptions heat left over from the
formation of the earth, and decay of radioactive
elements within the earth. Volcanic eruptions
account for a large proportion of the internal
heat that is dissipated from the interior of the
earth. Are Volcanic Eruptions Tied to Lunar
Cycle? Gravity is one of Earth's strongest
forces, so you can't ignore the moon. The
challenge is to find out just how it's playing a
role
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Japanese researchers put beakers of potassium
hydroxide, a strong, basic solution, on Honshu's
Asama volcano, which was beginning to show signs
of erupting. As the highly acidic gases released
by the crater seeped through holes in a crate
covering the beakers, they increasingly altered
the solution's composition in the months before a
large eruption. Today, volcanologists use
so-called "Japanese boxes" routinely, though
again they must check the beakers manually.
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Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI) Volcanic Explosivity Index (VEI)
Description Volume ofEjectedMaterial PlumeHeight EruptionType Duration TotalEruptionsGiventhis VEI Example VEI
Non-Explosive variable lt100m Hawaiian variable 699 Kilauea(1983 topresent) 0
Small lt.001 km3 100-1000m Hawaiian/Strombolian lt1 hr 845 Nyiragongo(1982) 1
Moderate .001-.01 km3 1-5km Strombolian/Vulcanian 1-6 hrs 3477 Colima(1991) 2
Moderate/Large .01-.1 km3 3-15km Vulcanian/Plinian 1-12 hrs. 869 Galeras(1924) 3
Large .1-1 km3 10-25km Vulcanian/Plinian 1-12 hrs. 278 Sakura-Jima(1914) 4
VeryLarge 1-10 km3 gt25 km Plinian/Ultra-Plinian 6-12 hrs. 84 Villarrica(1810) 5
VeryLarge 10-100 km3 gt25 km Plinian/Ultra-Plinian gt12 hrs. 39 Vesuvius(79 AD) 6
VeryLarge 100-1000 km3 gt25 km Ultra-Plinian gt12 hrs. 4 Tambora(1812) 7
VeryLarge gt1,000 km3 gt25 km Ultra-Plinian gt12 hrs. 0 YellowstoneCaldera(2 millionyears ago) 8
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Inflation begins as magma rises into the summit
reservoir. Tiltmeters measure changes in slope of
the ground. The Global Positioning System (GPS)
is used to measure the position of benchmarks. In
order to determine the deformation caused by an
episode of inflation, scientists must install and
survey the benchmarks and install tiltmeters and
GPS receivers (if continuous measurements are
desired) before magma moves
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• Tilt or uplift of the volcanic edifice
• inflation of volcano due to upwelling magma, and
  2. laser guided tilt-meters can record uplift as
  small as a few millimeters
• Using GPS for Monitoring Volcano Deformation
• Global Positioning Satellite (GPS)remote sensing

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Peak Inflation Inflating magma reservoir
results in deformation that is measured on the
surface. As the magma reservoir becomes inflated,
the ground around it cracks to accommodate its
increasing volume. Many small earthquakes occur
in the area surrounding the magma as the rocks
break. As the surface of the volcano changes
shape, tiltmeters record tiny changes in slope,
distances increase between benchmarks on opposite
sides of the caldera, and elevations of the
stations increase
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Eruption usually leads to deflation The summit
magma reservoir begins to deflate when magma
moves laterally into a rift zone and either
erupts or is stored there. At the summit,
tiltmeters record tilt toward the magma
reservoir, and GPS stations move toward the
reservoir. Near the eruption or intrusion,
however, tiltmeters record local ground inflation
and GPS stations move away from the erupting vent
or intrusion. Deflating magma reservoir.
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Before it erupts, a volcano produces many
thousands of earthquakes. Some of these happen
when rock inside the volcano cracks or slips
along a fault. Others are caused by magma (molten
rock) and gases trying to move under pressure
within channels and cracks
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Pressure from a pool of magma has just cracked
solid rock, creating a volcano-tectonic (VT)
event. This type of quake produces relatively
high-frequency shaking, usually between one and
five cycles per second
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Seismic Signal of Volcano-Tectonic (VT) Event A
VT event occurs when magma under pressure or
cooling rock causes rock to crack or slip. The
abrupt motion of the rock causes its seismic
signal to appear abruptly on a seismogram. Even
though the way they are produced is different,
seismograms produced by volcano-tectonic
earthquakes look like those produced by typical
earthquakes (those caused by the motion of
tectonic plates at plate boundaries, such as the
San Andreas fault and the Mid-Atlantic Ridge).
VT events cycle as many as five times a second,
particularly if the earthquake is two kilometers
(1.2 miles) or more below the surface. The
frequency of the VT signal shown here is five
cycles per second
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Long Period Event Sudden changes in pressure
within magma-filled cracks and channels cause
long-period (LP) events. LP events are
volcano-related earthquakes that are lower in
frequency than volcano-tectonic (VT) events. The
frequency of LP events is one half of a cycle to
three cycles per second. Unlike VT events, LP
events can reveal magma flow and the buildup of
pressure within a volcano. This knowledge can
help seismologists predict eruptions.
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The shaking that causes LP events is similar to
the "water hammer" that happens in household
water pipes. When water is moving quickly through
a pipe and the faucet is turned off, the water is
forced to stop. But instead of coming to an
abrupt stop, it bounces against the closed valve,
creating a wave of pressure that moves back and
forth within the pipe. The rate at which the wave
bounces is determined by the pipe's resonant
frequency, a natural frequency of vibration that
is, in turn, determined by several factors,
including its length and shape. This bounce
causes the pipe to clang loudly. The same thing
happens within a volcano's magma channel, except
that the channel's end is already closed, and the
abrupt change is caused by variations in the
magma's pressure. Also, the frequency of the
bounce is much slower within the channel.
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Tremor A tremor is a long-period (LP) event, but
one that lasts longer than the typical LP event.
In fact, a single tremor can last anywhere from
several minutes to months. The frequency range of
a tremor is the same as that with an LP event
one half of a cycle to three cycles per second.
The signal shown here has a frequency of two
cycles per second. Like LP events, tremors can
also be a good indicator of an impending volcanic
eruption.
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The source of a tremor can and often is the same
crack or channel that produces LP events. The
difference is that, with a tremor, the waves of
pressure traveling through the magma get a little
extra push every so often. This push can be
pressure changes coming through magma channels
from below. Because the waves creating the tremor
travel at the cracks' resonant frequency (see LP
section), the signal can appear as a continuous
wave moving at a single frequency.
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Hybrid Event Sometimes a volcano-tectonic (VT)
event triggers a long-period (LP) event, and vice
versa. A seismic signal that contains a mixture
of both types is called a hybrid. This hybrid
event is a VT event that triggered an LP event.
Notice how the signal is bunched up more at the
beginning than it is later on. The first part of
this signal shows the VT event later, the
less-bunched (lower frequency) signal of the LP
event appears
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Because LP events often begin with signals that
look very similar to those at the beginning of a
hybrid, it is usually difficult for seismologists
to distinguish between the two. To tell one from
the other, seismologists look closely at several
seismograms of a single event, as recorded by
seismographs placed at various locations. If the
first part of the signal looks similar on all of
the seismograms, they probably have an LP event.
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Devices such as Autonomous Underwater Hydrophone
(AUH) mooring, Are used to monitor marine
Volcanoes on the seafloor. This helps in
monitoring earthqauke generated tsunamis
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Hydrophones monitor many sources of oceanographic
sounds including marine mammals, earthquakes,
ships and waves. Sounds are transmitted over
great distances through the SOFAR channel, a
unique zone in the water that conserves the sound
signal
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Emergency management is a broad term and includes
the 4Rs Risk Reduction looking for ways of
reducing the consequences of hazards, such as
land use planning, building and safety codes,
insurance incentives, to name a few. To do this
effectively we need good information about
hazards and their impacts on communities. Readines
s increasing the understanding and awareness of
hazards through education programmes. Working
with the community to develop self-help
programmes such as household emergency plans and
business continuity plans. Ensuring plans and
systems are in place (and tested), that enable
agencies and communities to respond effectively
to an emergency. Response actions taken
immediately before, during or directly after an
emergency to save lives and property. To reduce
the damage and make sure we can respond as
effectively as possible, we need to have already
reduced the risk as much as possible and have
good response plans and procedures in place that
have been well rehearsed. Recovery as well as
coping with problems immediately after an
emergency, recovery programmes extend to
rebuilding and restoring the community. We may
look at rebuilding a community in a new way to
prevent a disaster from occurring again.
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Civil Defence is a component of emergency
management, relating mainly to Readiness and
Response activities. Hazards range from big
events such as volcanic eruptions, through to
floods and storms, fires, power failure, and
disease outbreaks. By working together in all
areas of emergency management we can create a
community which can reduce the impacts of hazards
and can bounce back. For more information contact
your local council, civil defence or emergency
management office.
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Volcanic ash can circle the earths atmosphere
and cause a blanket for the Suns radiation ro
reach ground, causing cooling.
Plinian Eruptions Vol Expl Index 6
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Wahaula Visitor Center, Hawaii Volcanoes National
Park, was one of more than 200 structures overrun
by lava flows (foreground) from the 1983-present
eruption at Kilauea Volcano. (Photograph by J.D.
Griggs, USGS.)
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Plume height refers to the highest point the
eruptive cloud reaches before it flattens out and
begins to drift downwind. Scientists estimate the
height by using visual observations from
observers on the ground or from pilots flying
nearby who compare the plume to their altitude.
More exact measurements are made using satellites
and radar
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Total Eruptions with this VEI Volcanologists have
rated over 6,000 eruptions that occurred within
the last 10,000 years. Most eruptions have a VEI
of 3 or less. Luckily, really big eruptions don't
happen very often. There are many volcanoes with
a VEI of 2 because scientists assign a 2 to any
volcano that they know was explosive but about
which they have no other information.
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The experience of that local population with
volcanic eruptions is usually limited, often
non-existent, as most volcanoes have major
eruptions less than once a century. The
volcanological community has experienced some
major successes in working with decision-makers
and the general public to mitigate the damage
from volcanic eruptions . The best tool for
public education found so far is videos of actual
eruptions and their consequences. Responsibility
for ordering volcano-inspired response (decisions
to limit access to, or require evacuation from,
certain areas, and for how long) usually rests
with local government officials and emergency
managers or civil defense personnel. There are
enormous social and economic costs to any
measures taken, and great resistance from almost
all components of the local community is the
norm. Even one instance of evacuation that in
hindsight comes to be viewed as a "false alarm"
can damage the credibility of both the officials
and the scientists whose information formed the
basis for the action, for many years.
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The Risk to Aviation from Airborne Volcanic Ash
Airborne volcanic ash is a serious aviation
safety hazard. In the past 20 years, more than 80
commercial aircraft have unexpectedly encountered
volcanic ash clouds in flight. Commercial
jetliners that have encountered volcanic ash
plumes have had all engines fail, with several
near-crashes. Abrasion to forward-facing
surfaces, including cockpit windows, the leading
edges of wings and control surfaces, engine
cowlings, etc., threaten safety and require
expensive repairs. Cockpit windows have been
pitted badly enough to endanger landing. Damages
to a single aircraft have reached 80 million. In
addition to these major repair costs from
encountering a heavier plume of ash, aircraft
flying through thinner plumes require increased
maintenance of engines and external surfaces.
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Responsibility for most aspects of volcano
monitoring is dispersed and usually quite local.
The directory of volcano-monitoring entities
issued by the World Organization of Volcano
Observatories (WOVO) lists 61 separate
observatories. Most of these focus on a single
volcano, and the levels of staffing,
instrumentation, computer support, and
communications links with the outside vary
greatly. Their strengths in the event of a
volcanic crisis are (a) familiarity with the
eruptive history and probable behavior of the
local volcano(es), (b) previously established
local credibility based on that knowledge, and
(c) established connections with relevant local
government officials and emergency responders. In
Hawaii, Hawaii Volcano Observatory is the federal
agency for the hazard monitoring.
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On average, about 15 major explosive
eruptionsthose powerful enough to inject ash
into the stratosphereoccur per year. Ash clouds
that reach above 25,000 ft. can travel hundreds
of miles. Giant plumes from a major eruption,
such as Mt. Pinatubo in 1991, can affect aircraft
thousands of miles downwind. When Mt. St. Helens
erupted in 1980, the plume reached an altitude of
90,000 ft. in 30 minutes and was 50 miles wide.
In 15 hours, the plume traveled 600 miles
downwind. After 2 weeks, ash had circled the
earth.
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Volcanoes pose a serious threat to persons on the
ground near erupting volcanoes (due to
proximal hazards such as lava flows, mud flows,
ash fall, etc). Ash clouds from major eruptions
endanger aircraft and airport operations over
distances of thousands of kilometers. Remote
sensing has become an indispensable part of the
global system of detection and tracking of the
airborne products of explosive volcanic eruptions
via a network of Volcanic Ash Advisory Centers
(VAACs) and Meteorological Watch Offices (MWOs).
Visible and InfraRed (IR) satellite data provide
critical information on current ash cloud
coverage, height, movement, and mass as input to
aviation SIGnificant METerological (SIGMET)
advisories and forecast trajectory dispersion
models. Recent research has also shown the
potential of remote sensing for monitoring
proximal hazards such as hot spots and lava flows
using geostationary and polar InfraRed (IR) data.
Also, Interferometric
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Synthetic Aperture Radar (InSAR) imagery has been
used to document deformation and topographic
changes at volcanoes. However, limited spatial
and temporal resolution of available satellite
data means that, for most proximal hazards, it is
used mainly as supplemental information for
current eruptions, and post-disaster assessment
in mitigation and prevention of future
disasters. Spectral bands used in detection of
volcanic ash and surface-based hazards are
identified in this report. They include a variety
of IR bands, especially those centered near 4,
7.3, 8.5, 11 and 12 microns. Visible (0.5 - 1.0
micron) and dual ultraviolet (UV) (0.3 - 0.4
micron) channels, although limited to daytime
use, are valuable for qualitative assessment of
ash and sulfur dioxide (SO2) plume coverage, and
quantitative estimation of ash optical depth, ash
cloud top height (through parallax techniques)
and total mass of silicate ash and SO2. The
minimum spectral channels needed for effective
remote sensing of volcanic hazards are specified
in the report and recommendations, as
are threshold and optimum spatial resolutions and
frequencies. Similar requirements are proposed
for some important derived products (ash cloud
height, ash column mass, and SO2 concentration).
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Volcanic Ash Plumes Volcanic ash poses a menace
to persons on the ground near erupting volcanoes,
and to aircraft over thousands of kilometers for
major eruptions. Volcanic eruption clouds
containing silicate ash particles, volcanic
gases, and acid aerosols can do extensive damage
to high altitude jet aircraft. When ingested into
jet engines, melted volcanic ash can block air
intakes, abrade turbine surfaces and blade tips,
and generally cause loss of engine performance
that could result in either emergency engine
shutdowns or compressor stall failures
(flameouts). Since volcanicaerosols (gases and
particulates) can be injected at all altitudes
from sea level to 150,000 ft (45,000 m) Above Sea
Level (ASL) or more, from perennially erupting
sources (e.g., Mt. Etna, Italy Mt. Sakurajima,
Japan) or from massive, explosive eruptions
(e.g., Mt. Pinatubo 1991), aircraft can be
affected at any operational altitude. Thus, ash
ingestion and abrasion risks can be experienced
by trans-continental and trans-oceanic aircraft
at cruising altitudes in the upper troposphere
and lower stratosphere, as well as by aircraft
operating near the ground in regions affected by
local plumes or ashfall.
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Areas of monitoring responsibility for the
Volcanic Ash Advisory Centers (VAAC) established
by ICAO. Shaded areas are unmonitored. (Courtesy
of D. Schneider, Alaska Volcano Observatory)
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Seismic Watch and Earthquake Warning Volcano
Watch and Volcano Warning Emergency Response
Team, County, State and Federal Emergency
Management Agency (FEMA), Homeland Security
Department Job of interpreting the data coming
in and of understanding what was about to happen.
complete a preliminary but extremely accurate
volcanic hazards assessment and a hazards
zonation map
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Even with equipment installed and the most
experienced team members that we can assemble,
it's extremely difficult to accurately forecast
exactly what the volcano is going to do, when
it's going to do it, and how big an eruption
there will be. Part of the frustration is that
scientists don't make decisions about land use,
or how to respond to the unrest, or whether or
not to evacuate. That's the reponsibility of
civil defense and elected officials. But these
are life-and-death decisions, and they have huge
political and economic consequences. If there's a
failed eruption, or a so-called "false alarm,"
everybody's angry, money is lost, and both
scientists and public officials lose credibility.
By the same token, if scientists don't understand
what's about to happen, or public officials don't
believe what the scientists think is about to
happen, and people are not evacuated, and an
eruption occurs and people are killed, then
everyone is even angrier. We do the very best we
can to provide good, accurate information to
public officials. But we're never in a position
where we can say we're confident that an eruption
will occur within "x" number of days and be of a
certain size and destroy a certain area
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The future of predicting
HVO press releases are issued to the local news
media when a significant change that affects the
active vent or seismic activity. When will
forecasting get better? It's improving year by
year. Every time we work on a volcano crisis, we
learn more about how to interpret the subtle and
sometimes very sophisticated signals that
volcanoes give as magma moves around. There are a
whole suite of different kinds of earthquakes,
for instance volcano tectonic earthquakes,
long-period earthquakes, volcanic tremor. It's a
very, very complicated business. However,
compared to earthquake predictions, we're
extremely lucky no one has any ability to
forecast earthquakes
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Bernard Chouet, USGS, (2002) has developed a
modelstrange seismic resonance coming from
volcanoes. In time he learned how these sounds
could signal a dangerous rise in pressure as
magma welling up from deep within the Earth tried
to find its way out if it didn't, the volcano
eventually blew The key principle is pressure,
and how fast you're pressurizing the volcanic
edifice. This is essentially a pressure-cooker
situation. The evidence of this pressurization
comes through the long-period events, which are a
manifestation of pressure accumulating and
magmatic or hydrothermal fluids -- mostly in the
form of gases -- trying to move in response to
this excess pressure and trying to shoot through
the available fractures and cracks that permeate
the edifice. A somewhat analagous situation is
what happens when you boil water in a teakettle.
When the water starts to boil, you have this
singing steam coming out of the teakettle. In a
way the volcano is also singing its song.
Individual long-period events are little chirping
sounds the volcano makes while pressurizing. When
the long-period events occur in rapid succession,
a sustained signal results. The volcano then is
literally singing its tune.
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This is a siren song because the volcano is
telling you, "I'm under pressure here. I'm going
to blow at the top. Scientists tracking active
volcanoes walk a tightrope when advising public
officials on the likelihood of an eruption. The
interface between the scientists monitoring a
volcano and public officials is very difficult.
Most people are willing to be evacuated once. But
if nothing happens, the loss of credibility could
cause people to ignore future warnings. Scientists
can't make the decision to evacuate. They
provide information on the hazards, and we are
working to do that. But using the
informationlong-range land-use planning,
development of early-warning systems, and
evacuation plansthat's up to public officials
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Monitoring Methods for Volcanic Hazards
Ground-based and airborne methods Satellite techniques
Seismic networks to monitor earthquakes, tremor, rockfall
Deformation networks to monitor tilt, expansion or contraction often in conjunction with GPS GPS, in conjunction with ground-based networksRadar, particularly InSAR
Monitoring changes in microgravity to detect magma intrusion
Observation of thermal emissions, measurements of temperature, airborne FLIR cameras Thermal IR
Gas emissions (SO2, CO2 levels or changes in gas ratios) via COSPEC, direct sampling, FTIR UV, IR (8.5 micron) can detect SO2 acid aerosols detectable by various UV, IR methods
Acoustic monitoring for debris flows and lahars
Mapping, photography to document stages of the eruption, distribution of eruptive products high-resolution panchromatic or multispectral imagery
Mapping to document topographic changes caused by the eruption, and to determine thickness of eruptive products high-resolution stereo panchromatic imagery, radar