Backgrounder: Volcanoes
From the Federal Emergency Management Agency (FEMA) - October 23, 2004
EMERGENCY INFORMATION
- Volcanic ash can affect people hundreds of miles away from the cone
of a volcano. Several of the deaths from the Mount St. Helens volcano
in 1980 were attributed to inhalation of ash. Volcanic ash can contaminate
water supplies, cause electrical storms, and collapse roofs.
- An erupting volcano can also trigger tsunamis, flash floods, earthquakes,
rockfalls, and mudflows.
- Sideways directed volcanic explosions, known as "lateral blasts,"
can shoot large pieces of rock at very high speeds for several miles.
These explosions can kill by impact, burial, or heat. They have been
known to knock down entire forests. The majority of deaths attributed
to the Mount St. Helens volcano were a result of lateral blast and tree
blow-down.
DANGER ZONES
Volcanic eruptions are most likely in the Pacific Rim states of Hawaii,
Alaska, Washington, Oregon, and California. The chance of eruptions that
could damage populated areas is the greatest for the active volcanoes
of Hawaii and Alaska. Active volcanoes of the Cascade Mountain Range in
California, Oregon, and Washington have created problems recently. The
danger area around a volcano covers approximately a 20-mile radius. Some
danger may exist 100 miles or more from a volcano, leaving Montana and
Wyoming at risk.
WHAT IS A VOLCANO?
A volcano is a mountain that opens downward to a reservoir of molten
rock below the surface of the earth. Unlike most mountains, which are
pushed up from below, volcanoes are built up by an accumulation of their
own eruptive products lava, ashflows, and airborne ash and dust. When
pressure from gases and the molten rock becomes strong enough to cause
an explosion, eruptions occur. Gases and rock shoot up through the opening
and spill over, or fill the air with lava fragments. Volcanic products
are used as building or road-building materials, as abrasive and cleaning
agents, and as raw materials for many chemical and industrial uses. Lava
ash makes soil rich in mineral nutrients.
HELP YOUR COMMUNITY GET READY
The media can raise awareness about volcanoes by providing important
information to the community. Here are suggestions:
- In a volcano prone area, publish a special section in your local
newspaper with emergency information on volcanoes. Localize the information
by including the phone numbers local emergency services offices, and hospitals.
- Feature an interview with a representative of the U.S.
Geological Survey, talking about how it determines the likelihood
of a volcanic eruption.
- Conduct a series on how to recognize the warning signals of a possible
volcanic eruption.
- Work with local emergency services and American Red Cross officials
to prepare special reports for people with mobility impairments on what
to do if an evacuation is ordered.
DID YOU KNOW...
- More than 80 percent of the Earth's surface above and below sea level
is of volcanic origin. The seafloors and some mountains were formed
by countless volcanic eruptions. Gaseous emissions from the volcanoes
formed the Earth's oceans and atmosphere.
- The May 18, 1980, eruption of Mount St. Helens in the Cascade Range
of southwestern Washington occurred after more than a century of dormancy.
The Mount St. Helens volcano took the lives of more than 58 people and
caused property damage in excess of $1.2 billion.
- The 1992 Mount Pinatubo eruption in the Philippines caused 342 deaths
and an evacuation of over a quarter of a million people. An eruption
of this size is likely to occur once every 200-400 years.
- There are more than 500 active volcanoes in the world. More than half
of these volcanoes are part of the "Ring of Fire," a region that encircles
the Pacific Ocean.
- The rock debris carried by a lateral blast at Mount St. Helens had
an initial speed of more than 250 miles per hour. Fifteen miles from
the volcano, the blast continued to move at a pace of approximately
60 miles per hour.
- Crater Lake in Oregon formed from a high volcano that lost its top
after a series of tremendous explosions approximately 6,600 years ago.
The information provided on this site is for informational purposes only.
Always consult your doctor for medical advice.
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