Volcanoes commonly occur in belts or clusters at plate boundaries. Forecasting volcanic eruptions involves assessing the character and timing based on the volcano's historic eruptions and measuring parameters like seismic activity, ground deformation, and gas emissions. Determining the timing of eruptions depends on monitoring these precursory signals.

2. Etna 2003

3. 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

4. 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.

5. Anatahan Volcano eruption, May 11, 2003
Northern Mariana Isles

7. 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.

9. 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?

14. 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.

16. Mt. Pagan, Northern Mariana, Guam, 1994

19. Kilauea, 1996.

22. 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

23. 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.

24. 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
1. 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
3. Atmospheric Disseminated ash-plume, Aviation hazard
4. Pollution, Vog, Haze, Global cooling

25. 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.
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.

26. 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.

27. 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

28. 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

29. 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

30. 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

31. 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.

32. Volcanic Explosivity Index (VEI)
Description
Volume of
Ejected
Material
Plume
Height
Eruption
Type Duration
Total
Eruptions
Given
this VEI Example VEI
Non-
Explosive
variable <100m Hawaiian variable 699 Kilauea
(1983 to
present)
0
Small <.001 km3 100-
1000m
Hawaiian/
Strombolian
<1 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
Very
Large
1-10 km3 >25 km Plinian/
Ultra-Plinian
6-12 hrs. 84 Villarrica
(1810)
5
Very
Large
10-100 km3 >25 km Plinian/
Ultra-Plinian
>12 hrs. 39 Vesuvius
(79 AD)
6
Very
Large
100-1000 km3 >25 km Ultra-Plinian >12 hrs. 4 Tambora
(1812)
7
Very
Large
>1,000 km3 >25 km Ultra-Plinian >12 hrs. 0 Yellowstone
Caldera
(2 million
years ago)
8

33. 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

34. Tilt or uplift of the volcanic edifice
1. 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
1. Global Positioning Satellite (GPS)remote sensing

35. 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

36. 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.

37. 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

38. 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

39. 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

40. 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.

41. 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.

42. 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.

43. 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.

44. 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

45. 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.

46. Devices such as
Autonomous Underwater
Hydrophone (AUH) mooring,
Are used to monitor marine
Volcanoes on the seafloor.
This helps in monitoring
earthqauke generated tsunamis

47. 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

48. Emergency management is a broad term and includes the ‘4R’s’:
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.
Readiness: 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.

49. 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.

51. Volcanic ash can circle the earth’s
atmosphere and cause a blanket
for the Sun’s radiation ro reach
ground, causing cooling.
Plinian Eruptions Vol Expl Index 6

52. 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.)

53. 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

54. 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.

56. 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.

57. 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.

58. 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.

59. On average, about 15 major
explosive eruptions—those
powerful enough to inject ash
into the stratosphere—occur 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.

60. 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

61. 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).

62. 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.

63. 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)

64. 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

65. 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

66. 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

67. Bernard Chouet, USGS, (2002) has developed a model:strange 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.

68. 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
information—long-range land-use planning, development of early-
warning systems, and evacuation plans—that's up to public officials

69. 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 networks
Radar, 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
Monitoring Methods for Volcanic Hazards