Volcanoes form when molten rock, or magma, erupts onto
the Earth’s surface. Most magma forms at plate boundaries within the Earth’s
crust or upper mantle. The molten rock migrates upward, coming to reside in
a "magma chamber" or reservoir below the surface. Magma
periodically rises from the magma chamber to the surface, causing eruptions.
Pressure builds up inside the Earth before an eruption
takes place. This pressure causes earthquakes, as the rock around the rising
magma shifts. Earthquakes in volcanic areas are thus often precursors to
Different types of volcanoes have different eruptive
styles, depending on the composition of the magma, its temperature, and how
fast it moves to the surface. Some volcanoes erupt very violently, spewing
pieces of ash, lava, and rock hundreds of meters into the atmosphere. For
example, Stromboli is a volcano in Sicily, Italy noted for its violent
eruptions. In contrast, Kilauea, a volcano in Hawaii has a quiet eruptive
style, lava slowly pours from its vents, flowing downhill.
In addition to lava, mudflows sometimes form during
eruptions. Mt. St. Helens, a volcano in Washington that erupted in 1980, is
a good example. Mt. St. Helens erupted violently. It literally "blew
its top off." However, there was a large amount of snow on top of Mt.
St. Helens, when it erupted. The heat of the explosion caused the snow to
melt. The resulting water mixed with the ash produced by the eruption, and
preexisting loose rock. The resulting mudflows cascaded down the slopes of
the volcano at over 120 miles per hour. They caused much damage in the
- Show the students pictures of erupting volcanoes. You may want to use
the images or websites mentioned in the Pre Lab.
- This exercise gives students skills in drawing an erupting volcano.
Before giving them the worksheet, discuss what an erupting volcano looks
like. Many times lava will cascade down the volcano and steam will come
from the erupting vent. You may also want to discuss the shape the
volcano will take after an eruption. It will be similar to the shape
before the eruption, but will be larger. (Note: there are exceptions to
this rule; some volcanoes are so explosive that the initial eruptions
actually blow parts of the volcano away, making it smaller).
- Instruct the students to draw an erupting volcano. In the picture,
they should draw the hot lava streaming down the sides of the volcano,
and the steam coming from its top. Help the students to draw the lava
and steam by putting the guide below on the board or projection screen.
When they have finished their drawing, have the students write a
sentence about their volcano in the space provided.