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Volcanoes
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Display Visual
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A Volcano Is . . .
A vent through which
molten rock escapes to the Earth’s surface.
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Explain that 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, ashflows, and ash. When pressure from gases
within the molten rock becomes too great, an eruption occurs.
Tell the group that the United States is third in the world, after Japan
and Indonesia, for the number of active volcanoes. Since 1980, as many as
five volcanoes have erupted each year in the United States.
Point out that eruptions are most likely to occur in Hawaii and Alaska.
For the Cascade Range in Washington, Oregon, and California, volcanoes
erupt on the average of one to two each century.
Also, when Cascade volcanoes do erupt, high-speed avalanches of
pyroclastic flows (hot ash and rock), lava flows, and landslides can
devastate areas 10 or more miles away. Lahars can inundate valleys more
than 50 miles downstream.
Emphasize that the
island of
Hawaii (the largest of
the Hawaiian islands) experiences thousands of earthquakes associated with
active volcanoes each year. While most of these are too small to feel,
about once a decade a large quake shakes the entire island and causes
widespread damage.
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Volcanoes
(Continued)
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Explain that volcanoes produce a wide variety of hazards that can kill
people and destroy property. Large explosive eruptions can endanger
people and property hundreds of miles away and can even affect the global
climate.
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Display Visual
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Volcanic Hazards
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Toxic gases
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Lava and pyroclastic flows
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Landslides
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Earthquakes
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Explosive eruptions
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Tell the group that volcanic hazards include:
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Toxic gases.
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Lava and pyroclastic flows.
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Landslides.
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Earthquakes.
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Explosive eruptions.
Point out that eruptions can be relatively quiet, producing lava flows
that creep across the land at 2 to 10 miles per hour (mph). Explosive
eruptions can shoot columns of gases and rock fragments tens of miles into
the atmosphere, spreading ash hundreds of miles downwind.
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Volcanoes
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Define lava flows as streams of molten rock that either pour from a
vent quietly or erupt explosively as lava fountains. Because of their
intense heat, lava flows are also great fire hazards. Lava flows destroy
everything in their path, but most move slowly enough that people can move
out of the way. The speed at which lava moves across the ground depends
on several factors, including the:
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Type of lava that has erupted.
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Steepness of the ground.
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Rate of lava production at the vent.
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Display Visual
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Accompanying Hazards
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Mudflows (including lahars)
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Flash floods
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Wildland fires
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Tsunamis
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Earthquakes
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Explain that volcanic eruptions can be accompanied by other natural
hazards, including:
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Mudflows (including lahars).
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Flash floods.
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Wildland fires.
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Tsunamis (under special conditions).
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Earthquakes.
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Volcanoes
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Emphasize that historically, lahars have been one of the deadliest
volcano hazards. Lahars are mudflows or debris flows composed mostly of
volcanic materials on the flanks of a volcano. These flows of mud, rock,
and water can rush down valley and stream channels at speeds of 20 to 40
miles per hour and can travel more than 50 miles.
Caution the group that lahars can occur both during an eruption and when a
volcano is quiet. The water that creates lahars can come from melting
snow and ice, intense rainfall, or the breakout of a summit crater lake.
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Ask Question
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What are some hazards associated with volcanic ash? |
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Allow the group time to respond. Then, use the visual to elaborate on the
hazards.
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Volcanoes
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Display Visual
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Volcanic Ash Will . . .
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Cause severe respiratory problems.
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Diminish visibility.
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Contaminate water supplies.
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Cause electrical storms.
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Disrupt the operation of machinery.
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Collapse roofs.
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Explain that volcanic ash is actually fine, glassy rock fragments
that can affect people and equipment hundreds of miles away from the cone
of the volcano. Volcanic ash will:
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Cause severe respiratory problems.
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Diminish visibility.
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Contaminate water supplies.
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Cause electrical storms.
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Disrupt the operation of all machinery.
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Collapse roofs.
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Volcanoes
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Ask Question
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How can you prepare for volcanic eruptions? |
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Allow the group time to respond. Then, display the visual.
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Display Visual
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Volcanic Eruption
Preparedness
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Understand the risk.
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Talk to your insurance agent.
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Prepare a disaster supply kit.
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Develop an evacuation plan.
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Emphasize key steps in volcanic eruption preparedness:
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Understand the risk. Take time to learn about the risk from volcanic
eruption in your area.
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Talk to your insurance agent. Find out what your homeowner’s policy will or will not
cover in the event of a volcanic eruption.
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Prepare a disaster supply kit, including goggles and dust mask for every family
member.
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Develop an evacuation plan. Everyone in your family should know where to go if
they have to leave.
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Volcanoes
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Ask Question
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What should you do during a volcanic eruption? |
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Allow the group time to respond. Summarize the discussion using the
information from the visual below.
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Display Visual
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During a Volcanic Eruption
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Follow evacuation orders.
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Avoid areas downwind and river valleys downstream.
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If outside, protect yourself from ashfall.
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Be prepared for accompanying hazards.
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Be
sure to make the following points:
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Follow evacuation orders. Staying at home to wait out an eruption, if you are in
a hazardous zone, could be very dangerous. Take the advice of local
authorities.
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Avoid areas downwind 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 exposed further to volcanic eruption hazards.
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If outside, protect yourself from ashfall.
Volcanic ash will cause severe injury to breathing passages, eyes, and
open wounds, and irritation to skin.
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Be prepared for accompanying hazards.
Know how to respond to reduce your risk.
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Volcanoes (Continued)
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Suggest that the participants take the following measures to protect
themselves from ashfall:
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Wear long-sleeved shirts and long pants.
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Use goggles to protect your eyes.
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Wear eyeglasses instead of contact lenses.
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Use a dust mask or hold a damp cloth over your face to help you breathe.
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Ask Question
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What should you do after a volcanic eruption? |
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Allow the group time to respond. Summarize the discussion using the
information from the visual below.
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Display Visual
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After a Volcanic Eruption
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Stay away from volcanic ashfall areas.
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Clear roofs of ashfall.
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Avoid driving in heavy ashfall.
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If you have a respiratory ailment, avoid contact with any amount of
ash.
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Be
sure to make the following points:
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Stay away from volcanic ashfall areas.
The fine, glassy particles of volcanic ash will increase the health risk
to children and people with existing respiratory conditions such as
asthma, chronic bronchitis, or emphysema.
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Clear roofs of ashfall. Ashfall is very heavy and can cause roofs to collapse,
especially if made wet by rainfall. Exercise great caution when working
on a roof.
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Volcanoes
(Continued)
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Avoid driving in heavy ashfall. Driving will stir up volcanic ash that can clog
engines and stall vehicles. Moving parts, including bearings, brakes, and
transmissions, can be damaged from abrasion.
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If you have a respiratory ailment, avoid contact with any amount of
ash. Stay
indoors until local health officials advise that it is safe to go outside.
Ask the participants if there are any additional questions, comments, or
concerns, about volcanic eruptions.
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