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Section 10-1
• What is a volcano?
• Describe the process that causes a volcano.
• Define vent and crater.
• Explain the three kinds of places that
volcanoes are likely to be found.
• A volcano is an opening in Earth’s surface
that forms a mountain when layers of
lava and volcanic ash erupt and build up.
• Most of Earth’s volcanoes are dormant,
which means that they are not currently
active.
• Active volcanoes sometimes spew steam,
smoke, ash, cinders, and flows of lava.
What Causes Volcanoes?
• Volcanoes occur when magma, which is less
dense than the rock around it, is slowly forced
upward towards the Earth’s surface.
• After many thousands or millions of years,
lava flows out through an opening in Earth’s
surface. As the lava flows, it cools and
becomes solid, forming igneous rock.
• A vent is an opening
in Earth’s surface
through which lava,
ash, cinders, smoke,
and steam can flow.
• A crater is the steepwalled depression
around a volcano’s
vent.
Crater
• Volcanoes can occur at divergent boundaries
which are areas where Earth’s plates are
moving apart.
• Where the plates separate, they form long,
deep cracks called rifts.
Iceland was made
from a rift on the
Mid-Atlantic Ridge.
• Volcanoes can also occur at convergent
boundaries which are areas where Earth’s
plates move together.
• When plates converge, one plate slides under
another plate where the plate melts and is
forced upward in a volcano.
• Examples of volcanoes formed by convergent
boundaries are found around the Pacific Plate,
which is known as the Pacific Ring of Fire.
• Lastly, volcanoes can occur at hot spots, areas
in Earth’s mantle that are hotter than
neighboring areas, forming melted rock that
rises toward the crust.
• The Hawaiian Islands were formed from hot
spots.