Download Igneous Rock Features

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Shield volcanoes
Cinder cone volcanoes
Composite volcanoes
Lava plateaus
Calderas
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Formed from pure
basalt (low silica
magma) at hot spots
(like Hawaiian
Islands) or divergent
boundaries (like the
Mid-Atlantic Ridge).
Iceland is a shield
volcano formed where
a hot spot exists that
is also at the MidAtlantic Ridge.
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Paracutin in
Mexico is a famous
cinder cone, which
formed in a
cornfield in 1943.
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These volcanoes
occur on subduction
zones, and are
known for explosive
eruptions.
They erupt with ash,
cinders, and lava
bombs.
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The largest volcanoes, these form at subduction
zones, and can be either explosive (ash, cinders,
lava bombs) or quiet (liquid lava) eruptions.
Mount Fuji in Japan
Mount St. Helens in Washington State
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Sometimes thin, runny lava can flow out of
long cracks and travel far before cooling
The Columbia Plateau covers parts of WA, OR,
ID
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When a volcano stops erupting, sometimes
the top of the volcano’s crater collapses on
itself and leaves a depression.
If the area is rainy, the caldera can fill with
water.
Crater Lake in Oregon is one of the most
famous calderas.
Crater Lake from
above
Crater Lake, a caldera, and
Wizard Island, a small cinder
cone volcano formed much later
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Even the most explosive volcanoes
eventually stop erupting.
Igneous rock is rock that is formed from
cooled magma or lava.
Erosion and uplift can cause
underground igneous rock formations to
be seen on the Earth’s surface.
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A volcanic neck is formed when magma
hardens inside the pipe of a volcano
The soft cone erodes (usually from a cinder
cone volcano), and the harder igneous rock
remains and is exposed.
They look like the inside of a volcanic vent.
Some famous ones are Ship Rock, New Mexico
and Devil’s Tower in eastern Wyoming
•Devil’s Tower is a
famous volcanic neck
in Wyoming
•Devil’s Tower is
considered sacred
ground for Native
Americans.
•There are many folk
tales about how Devil’s
Tower was created.
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Dikes are formed when magma squeezes into
vertical cracks in rocks below the surface and
hardens.
When exposed due to erosion or uplift, this
looks like vertical stripes in rock.
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Sills are formed when magma squeezes into
horizontal cracks in rocks below the surface
and hardens.
When exposed due to erosion or uplift, this
looks like horizontal stripes in rock.
When memorizing the difference between
dikes and sills, remember that sills are
horizontal (go across) like “window sills.”
•Formed when magma cools underground
before reaching the surface
•Look like big domes of rock that can be exposed from
erosion
Batholiths are found
in Yosemite National
Park in California.
These are some of
the most famous
batholiths in
the country
That North Face jacket you
love? It’s named for the
“north face” or steep side of
Half Dome
Hiking up the “other side” of
Half Dome is a 12-13 hour
round trip hike, one of the
most strenuous in the National
Park system, with a 7800 foot
elevation change.
The Bousquet family climbed
Half Dome in July of 2012.
After climbing
granite “steps” for
hours,
we were glad to
travel through a
pine forest
for both the shade,
and the relatively
flat terrain.
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In all forms of intrusive (underground)
igneous rock formations, the steps are:
A volcano erupts
The volcano stops erupting (sometimes many
years later)
The un-erupted magma cools underground.
Sometimes it squeezes into cracks since it’s
liquid and less dense
Erosion wears down the rock around the
igneous rock, exposing the rock formation
From inside the lava tube (cave)
Outside the cave entrance