Download Volcanoes form as molten rock erupts.

KEY CONCEPT
Volcanoes form as
molten rock erupts.
STANDARDS
8–3.7 Illustrate the creation and changing of
landforms that have
occurred through geologic processes (including volcanic eruptions
and mountain-building
forces).
BEFORE, you learned
NOW, you will learn
• Magma is molten rock inside
Earth
• Magma forms as a plate sinking
in a subduction zone starts
to melt
• Volcanoes can form over hot
spots far from plate boundaries
• Where most volcanoes
are located
• How volcanoes erupt
• What types of volcanoes
there are
EXPLORE Eruptions
What happens when a volcano erupts?
PROCEDURE
1
VOCABULARY
Add water to an empty film canister until
it is three-fourths full.
2 Drop an antacid tablet in the water and put
volcano p. 262
lava p. 263
pyroclastic flow p. 264
the lid on the canister. Observe what happens.
MATERIALS
• empty film
canister
• effervescent
antacid tablet
• water
WHAT DO YOU THINK?
• What happened to the water and to the
canister lid?
• What caused the changes you observed?
• How might the events you observed be
similar to the eruption of a volcano?
Volcanoes erupt many types of material.
VOCABULARY
Make a word triangle for
volcano in your notebook.
Earth’s thin outer layer is made of cool rock, but most of Earth is made
of extremely hot rock and molten metal. Some of the heat inside Earth
escapes to the surface through volcanoes. A volcano is an opening
in Earth’s crust through which molten rock, rock fragments, and hot
gases erupt. A mountain built up from erupted material is also called
a volcano.
A volcano may erupt violently or gently. A violent eruption can
cause tremendous destruction even if not much molten rock reaches
the surface. For example, a volcano might throw out huge amounts
of rock fragments that start fires where they land or fall in thick layers
on roofs, causing them to collapse. A volcano can erupt gently yet pour
out rivers of molten rock that flow long distances. The violence of an
eruption depends mainly on the type of magma feeding the volcano.
262 Unit 2: The Changing Earth