Download VOLCANOES

Volcanoes
What are volcanoes?
A
volcano is
an opening in
Earth that
erupts gases,
ash, and lava.
How do volcanoes form?
 Magma
is less dense than the rock
around it, so it is forced toward the
surface
 Vent:
Opening that magma flows
through
 Crater:
The steep-walled depression
around a volcano’s vent
Where do volcanoes occur?

Divergent Plate Boundaries
– Plates move apart as magma comes up
forming a volcano
 Convergent Plate Boundaries
– Oceanic Plates subduct under
Continental Plates and melt into magma
that will sometime rise to form a volcano
Where do volcanoes occur?
Where do volcanoes occur?
 Hot
Spots
– Areas between Earth’s mantle and core
that are unusually hot.
Example:
– Hawaiian Islands
 Pacific Plate moving over a stationary
hot spot.
Hot Spot Occurrence
Liquid Hot Magma!!!!
What controls eruptions?
The
more trapped gases,
silica and water vapor the
more explosive the eruption.
What controls eruptions?
– quiet eruption -> Basaltic Magma, silica
poor
– Silica Rich: explosive eruption
Granitic Magma, Mount St. Helens,
WA
– Intermediate Silica: Quiet / explosive
eruption.
 Andesitic Magma, Convergent Plate
Boundaries, Krakatau, South America

Forms of Volcanoes

Shield Volcano
– Quiet eruptions
– Silica poor
– Basaltic lava
– Layers buildup
and form a
broad volcano
with gently
sloping sides
– Example:
Hawaiian
Islands
Forms of Volcanoes

Cinder Cone
Volcanoes
– Explosive
eruptions
– Silica rich
– Granitic lava
– Steep sides of
loosely packed
tephra (ash)
– Paricutín,
Mexico
Crater lake Cinder Cone
Forms of Volcanoes

Composite Volcano
– Varying
explosions depend
on amount of
silica and trapped
gases.
– Andesitic lava
– Dome shaped
– Mount Saint
Helens, WA
Violent Eruptions

1883: Krakatau,
Indonesia

1906: Vesuvius,
Italy

1983: Kilauea,
Hawaii

2000: Popocatepetl,
Mexico