BACKGROUND:
Earthquakes and volcanoes cause damage not only to
humans and their structures, but to the environment and wildlife.
Earthquakes can cause damage by shaking, tsunami’s, and
landslides. Volcanoes can cause damage by ash flows, release of gases,
mudflows, lava flows, and landslides.
Earthquakes may be associated with volcanic hazards,
especially as a precursor to an eruption. However, earthquakes can cause
disasters without the help of a volcano. Earthquakes generate seismic waves
that can release great energy. But if the earthquake occurs in an area that
is not populated, it is not a human disaster.
Volcanic damage occurs because of the products
generated by an eruption. The type of eruption is important. For instance, a
quiet lava eruption gives human enough time to evacuate an area. Violent
eruptions that occur with little warning are sometimes difficult to avoid.
Many people do not believe that volcanoes can cause much damage, and refuse
to move.
Volcanoes erupt differently, depending on the
composition and thickness of the erupting lava, the amount of gas in the
parent magma, and force of the eruption. Volcanoes that erupt lava that is
low in silica and gases tend to be "quiet," mostly pouring out
streams of fairly fluid lava. Kilaeua volcano in Hawaii is a good example.
Volcanoes that erupt silica-rich magmas, and that have a lot of gas, tend to
be explosive. This produces tremendous clouds of volcanic ash, ash flows,
and gases. The loose material produced by these eruptions often becomes the
raw material for landslides or mudflows. can cause dangerous explosions as
well as gentle lava flows.
PROCEDURE:
- With the class, review that earthquakes and volcanoes are dangerous.
Explain that every year, they cause damage not only to humans, but to
the environment and wildlife as well. Earthquakes cause damage to structures that cannot withstand shaking. Volcanoes can cause dangerous
explosions as well as gentle lava flows. Explain that this unit will
concentrate on volcanic hazards. Remind the students that after an
eruption, life will come back in due time.
- Show the class the slides of the aftermath of the 1980 Mt. St. Helens
eruption and other disasters in the Volcano Slideshow. The remaining
slides show different types of hazards, ranging from flowing lava to
violent eruptions causing great plumes of ash and debris to explode from
a volcano.
- Show the students the image below, or draw it on your board. Make sure
that the students understand that water (melted snow) mixes with ash to
form mudflows. Ask students if the shape of a volcano determines if the
mud moves slowly or fast. The steeper the slopes of a volcano, the
faster the mudflow will "ride down" its flanks. In the lab,
students will learn that the more viscous (thicker) the material, the
faster it will flow.
