What IS A VOLCANO?
A volcano is a place where magma
reaches the surface through a
conduit and bec0mes lava.
…
Window into the
Earth’s interior.
There are three types of volcanoes:
Shield Volcano:
A gently-sloped volcano.
Cinder Cone:
A volcano made of cinders
that are blown into the air.
Composite:
A volcano built of alternating layers
of cinders and lava.
What kind of volcano is this?
Mount Shasta is a composite
volcano.
Over the last 10,000 years,
Mt. Shasta has erupted on
average once every 800
years. During the 3,500
years the volcano has
erupted about once every
300 years. The most
recent eruption may have
occurred in 1786 A.D.
What kind of volcano is this?
Diamond Head is an eroded
Cinder (Tuff) Cone.
Early sailors mistakenly
thought glistening calcite
crystals inside the tuff
rocks were diamonds,
leading to the incorrect
name. Diamond Head
formed when hot magma
rising up a conduit hit
ocean water, causing large
explosions that threw
exploded magma particles
(tuff) into a broad ring.
What kind of volcano is this?
Kohala is a shield volcano.
• Kohala is the oldest of
the subaerial
volcanoes that make
up the Island Of
Hawaii. Kohala is
considered to be
extinct because it has
not erupted for 60,000
years.
obsidian
pumice
Examples of
volcanic rocks
volcanic glass
Q.Where are most found?
A.The “ring of fire”
What comes out of volcanoes
via eruptions?
• Lava flows
• Gases (primarily H2O vapors)
• Pyroclastic materials: rock and lava
fragments: ash; pumice; lapilli (little
stones); cinders; bombs
Types of Lava Flows
• Pahoehoe
• A’a
• Blocky
• 90% of lava is Basaltic
‰
PAHOEHOE – has a shiny, smooth, glassy
surface. It tends to be more fluid (lower
viscosity), hence flows more quickly and
produces thinner flows (typically 1-3 m).
‰
‰
Pahoehoe
A’A – a rubble flow, with a molten core, with
higher viscosity (but same composition) which,
therefore, tends to move slowly and produce
thicker flows (typically 3-20 m).
A’a
BLOCKY – similar to A’a, but even thicker
(>20 m), with a blocky rather than rubbly
surface. Andesites, dacites and rhyolites tend
to form blocky flows.
Blocky