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Volcanoes |
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July 2004
Produced by the National Disaster Education Coalition, Washington, D.C.
Volcanoes
Why talk about volcanoes?
Volcanoes produce a wide variety of hazards that can kill people and destroy
property. Volcanic eruptions fall into two broad types: (1) explosive and (2)
quiet. Hazards
from large explosive eruptions include widespread ashfall (fine glass particles),
pyroclastic flows (mixtures of hot gases and pumice blocks), and massive lahars
(volcanic
mud or debris flows) that can endanger people and property nearby as well as
tens
to
hundreds of miles away. Eruptions can even affect global climate. Hazards from
quiet lava
flows include igniting fires and producing chlorine-rich gas clouds where lava
pours
into the sea. Since 1980, as many as five volcanoes have erupted each year in
the United States. Eruptions are most likely to occur in Hawaii and Alaska. In
the Cascade Mountain Range in Washington, Oregon, and northern California, volcanoes
erupt
on the average of one to two or more each century.
Volcanic ash can affect people and equipment hundreds of miles from the volcano.
Inhaling
volcanic ash can cause serious respiratory problems for people with
heart and lung ailments.
Explosive eruption columns pose a serious hazard to commercial aviation. The
ash column can grow rapidly and reach more than 12 miles (19 kilometers) above
a
volcano in less than 30 minutes, forming an ash cloud. During the past 14 years,
about
80 commercial jets have been damaged by inadvertently flying into ash clouds,
and
several have nearly crashed because of engine failure. Many federal agencies,
including
the U.S. Geological Survey, the Federal Aviation Administration, and the National
Weather Service, are working together to issue timely warnings of airborne ash
to airports
and airline pilots.
What are volcanoes, and what causes them to erupt?
A volcano is a vent through which molten rock escapes to the earth’s surface.
Unlike other mountains, which are pushed up from below, volcanoes are built by
surface accumulation of their eruptive products—layers of lava flows, ash
flows,
and ash. When pressure from gases within the molten rock becomes too great, gases
drive the
molten rock to the surface and an eruption occurs.
Learn about your community’s risk from hazards created by volcanic eruptions.
While you may be located far from a volcano, the ash from an explosive eruption
could affect your area. Contact your local emergency management office, local
American Red Cross chapter, or state geological survey or department of natural
resources. Ask about the type of volcano hazards that could affect your area
and what you can do to prepare.
What damages can volcanoes cause?
In the past few thousand years, the volcanoes of the Cascade Mountain Range,
which stretches from northern California into British Columbia, have produced
more
than 100 eruptions, most of them explosive. However, individual Cascade Range
volcanoes
can lie dormant for many centuries between eruptions, and the great risk posed
by
volcanic activity in the region is therefore not always apparent. When Cascade
Range volcanoes do erupt, high-speed avalanches of hot ash and rock (pyroclastic
flows), lava
flows, and landslides can devastate areas 10 miles (16 kilometers) or more away,
and huge mudflows of volcanic mud and debris (lahars) can inundate stream valleys
at speeds
of 20 to 40 miles (32 to 64 kilometers) per hour and travel more than 50 miles
(80 kilometers) downstream.
Most eruptions at Hawaiian volcanoes are not explosive and are characterized
by the relatively quiet outflow of very fluid lava. These quiet eruptions can
produce
spectacular lava fountains or lava flows that creep across the land at the relatively
slow
speed of 10 miles (16 kilometers) per hour or so. The speed at which lava moves
across the
ground depends on several factors, including the type of lava erupted, the steepness
of the ground, and the rate of lava production at the vent. Because the temperature
of the lava can be 1000° to 2000° F (538° to 1093° C), lava flows
destroy
everything in their path, often causing dangerous fires. While most lava moves
slowly enough that people
can get out of the way, wildland fires can advance rapidly. Before and during
an
eruption, many small earthquakes occur as molten rock forces its way through
the
upper
parts of a volcano’s interior. Such quakes often provide early warnings
of changes
in eruptive activity.
Volcanic eruptions can be accompanied by other natural hazards: earthquakes,
mudflows
and flash floods, rockfalls and landslides, wildland fires, and (given
certain
conditions) tsunamis.
How can I protect myself from the ill effects of a volcanic eruption?
You need to know the volcanic hazards associated with active and potentially
active volcanoes where you live and where you visit. You must determine the varying
degrees of your own risk and take actions to stay safe and protect your property.
Learning
your community’s warning system, developing and practicing a household
evacuation
plan, and being prepared to shelter-in-place should be important parts
of your plan.
What is the best source of information in case of a volcano watch or warning?
Local radio or television stations are the best sources of information in a volcanic
eruption
situation. Volcanoes usually give warning that they will erupt, and U.S. Geological
Survey
(USGS) scientists have developed a forecasting system to alert public officials
and
the general public of such warnings. The USGS Volcano Hazards Program, in collaboration
with federal, state, and local government agencies, universities, and the private
sector, operates five volcano observatories to reduce the risk from volcanic
activity.
The five observatories are the Alaska Volcano Observatory, the Hawaiian Volcano
Observatory, the Cascades Volcano Observatory, the Long Valley Caldera Observatory,
and the Yellowstone Volcano Observatory.
If you are at risk from volcanic activity, you should:
• Learn about your community’s warning systems and emergency plans. Different
communities have different ways of providing warnings and different response
plans.
• Keep handy a pair of goggles and a dust mask for each member of your household
in case of ashfall.
• Develop an evacuation plan for volcanic eruptions and make sure all members of
your
household know and practice it. (See Evacuation and Sheltering, and
Postdisaster Safety.) Be sure to include your animals in your evacuation
plan.
Making plans at the last minute can be upsetting and wastes precious time.
• Discuss volcanoes with members of your household. Discussing volcanic eruptions
ahead of time helps to reduce fear and lets everyone know how to respond.
• Review landslide and mudflow safety and preparedness measures with members of
your household. (See Landslides.)
• Talk to you insurance agent. Find out what your homeowners’ policy will
or will not cover in the event of a volcanic eruption.
What to Do During a Volcanic Eruption
For general preparedness, every household should create and practice a Family
Disaster Plan and assemble and maintain a Disaster Supplies Kit. In addition,
every household should take volcano-specific precautions and plan for and practice
what to do if a volcano erupts.
You should:
• Listen to a local station on a portable, battery-operated radio or television
for updated emergency information and instructions. If the electricity is out,
this
may
be your main source of information. Local officials will give the most appropriate
advice
for your particular situation on local media.
• Follow any evacuation orders issued by authorities, and put your Family Disaster
Plan into action. Although it may seem safe to stay at home and wait
out
an eruption, if you are in a hazard zone, doing so could be very dangerous. The
best way to stay safe is to take the advice of local authorities.
• If indoors, close all window, doors, and dampers to keep volcanic ash from entering.
• Put all machinery inside a garage or barn to protect it from volcanic ash. If
buildings
are not available, cover machinery with large tarps.
• Bring animals and livestock into closed shelters to protect them from breathing
volcanic
ash.
• If outdoors, take shelter indoors. Your safest place is indoors, away from various
hazards.
• Stay out of designated restricted zones. Effects of a volcanic eruption can be
experienced
many miles from a volcano.
• Avoid low-lying areas, areas downwind of the volcano, and river valleys downstream
of the volcano. Debris and ash will be carried by wind and gravity.
Stay in areas where you will not be further exposed to volcanic eruption hazards.
Trying
to watch an erupting volcano up close is a deadly idea.
If you are caught in an ashfall:
• Wear a dust mask designed to protect against lung irritation from small particles.
•Protect your eyes by wearing goggles. Wear eyeglasses, not contact lenses.
• Keep as much of your skin covered as possible.
What to Do After a Volcanic Eruption
You should:
• Stay indoors and away from volcanic ashfall areas if possible. The fine, glassy
particles
of volcanic ash can increase the health risks for children and people
with
respiratory conditions, such as asthma, chronic bronchitis, or emphysema.
Whether you are indoors or outdoors:
• Wear a dust mask designed to protect against lung irritation from small particles.
•Protect your eyes by wearing goggles. Wear eyeglasses, not contact lenses.
•Keep as much of your skin covered as possible.
When it is safe to go outside:
• Clear roofs of ashfall. Ash is very heavy and can cause buildings to
collapse, especially if made wet by rain. Exercise great caution when working
on a roof.
• Avoid driving in heavy ashfall. Driving will stir up volcanic ash that
can clog engines and stall vehicles. Abrasion can damage moving parts, including
bearings,
brakes, and transmissions.
• Keep animals away from ashfall and areas of possible hot spots. Wash animals’ paws
and fur or skin to prevent their ingesting or inhaling ash
while grooming themselves.
Media and Community Education Ideas
• Ask your local newspaper or radio or television station to:
-Do a series on the dangers of volcanic eruptions, ashfalls, floods, etc.
-Do a story featuring interviews with local officials about land use management
in low-lying areas.
-Highlight the importance of staying informed about local conditions.
-Run public service ads about how to protect lives in the event of a volcanic
eruption.
-Feature an interview with a representative of the U.S. Geological Survey, talking
about
how this group determines the likelihood of a volcanic eruption.
-Do a series on local volcanic hazards and how to recognize the warning signs
of a possible volcanic eruption.
-Publicize emergency evacuation routes.
• Help the reporters to localize the information by providing them with
the local emergency telephone number for the fire, police, and emergency medical
services
departments (usually 9-1-1) and emergency numbers for the local utilities and
hospitals.
Also provide the business telephone numbers for the local emergency management
office, local American Red Cross chapter, and state geological survey or department
of natural resources.
• Work with officials of the local fire, police, and emergency medical services
departments;
utilities; hospitals; emergency management office; and American
Red
Cross chapter to prepare and disseminate guidelines for people with mobility
impairments
about what to do if they have to evacuate.
Facts and Fiction
Fiction: Volcanoes erupt with regularity.
Fact: Volcanoes generally experience a period of closely spaced
eruptions followed by long periods of quiet. Most volcanoes show no regularity,
and thus on the basis
of past history alone cannot be considered "overdue" or "ready
to blow."
Fiction: Volcanoes are unpredictable, erupting at any time without warning.
Fact: Volcanoes usually give warning signs that they are going
to erupt weeks to months or more in advance. Although we cannot predict when
a
volcano will start
to be restless, once activity begins, scientists can make general forecasts about
how
soon an eruption will occur. A more difficult challenge for volcanologists is
forecasting
the size of an impending eruption.
Fiction: Lava flows are the most significant hazards from volcanoes
in the United States.
Fact: Although this is true in Hawaii, the hazards differ at
the more than 150 volcanoes in other parts of the United States. Principal hazards
outside Hawaii include:
(1) Volcanic ashfall resulting from explosive-style eruptions. Volcanic ash,
the
shattered
remnants of volcanic rock, rises into the atmosphere, where it is a hazard to
aircraft and
affects large areas downwind when it falls back to earth. Where it falls in sufficient
quantity,
it can cause difficulties for vehicles, machinery, and utilities, and can be
injurious
to human health.
(2) Volcanic mudflows (lahars) resulting from the sudden melting
of snow
and ice during eruptions. Lahars can inundate river valleys tens of miles distant,
destroying
bridges, highways, and other types of development, as well as endangering people.
Fiction: Earthquakes cause volcanic eruptions.
Fact: Earthquakes indicate a geologically active landscape,
but they are not the cause of volcanic eruptions. In rare cases, large tectonic
earthquakes have triggered
eruptions of nearby volcanoes that have been poised to erupt anyway. In the case
of Mount
St. Helens, a flurry of earthquakes under the volcano suggested potential eruptive
activity.
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