Volcano:
an opening in the earth’s surface
through which lava, hot gases, and
rock fragments erupt
How do they form?
 Magma 50-100 miles below the
earth’s surface slowly begins to rise
to the surface
 As the magma rises it melts gaps in
the surrounding rock
 As more magma rises a large
reservoir forms as close as 2 miles
below the surface (magma chamber)
How do they form?
 Pressure from the surrounding
rock causes the magma to blast
or melt a conduit (channel) to the
surface where magma erupts onto
the surface through a vent
(opening)
How do they form?
 The magma, now called lava, builds
up at the vent forming a volcano
How do they Form?
 Often the volcano sides will be
higher than the vent forming a
depression called a crater
Crater:
Caldera:
an unusually large crater or the
remains when the cone collapses
into its own magma chamber
The Birth of a Volcano
Anatomy of a Volcano
Cone:
the above ground structure
built from lava and/or tephra
Conduit:
the path that magma takes from
the magma chamber to the vent
Magma Chamber:
the reservoir located under the
volcano where magma collects and
becomes the supply of magma/lava
to build the volcano
Lava:
molten, liquid rock on the surface
of the earth
Parasitic Cone:

a smaller secondary volcano built
on the side of or near the main
volcano, but sharing the same
conduit to the magma chamber
Fumarole:
a secondary vent that emits
only gases
Fissure:
a long fissure (crack) from
which lava flows
Vent: opening of the volcano, through which lava,
ash and gases flow
Take a minute to
label the parts on
the diagram (not
all parts are
shown)
Crater
Ash Cloud/Gases
Parasitic Cone
mantle
Vent
Lava Flow
conduit
Magma chamber
Types of
Volcanic Eruptions
Two factors determine the type of
eruption:


Amount of water vapor &
other gases in the magma
The chemical composition of
the magma
Explosive Eruptions

Trapped gases
under high
pressure will
violently
explode when
the magma
reaches the
lower pressure
of the surface.
Explosive Eruptions

Has granitic
magma is very
thick and plugs
the vent
causing the
pressure to
build until it
blows violently
out the vent
Mt. St. Helens
Explosive Eruptions

The high
water content
of the magma
produces more
water vapor
which when
mixed in
granitic
magma
produces
explosive
eruptions
Mont serrat
Explosive Eruptions-Examples
Mt. Fuji
Mt. Pinatubo
Mt. St. Helens
Eruption of Mt. St. Helens
Quiet Eruptions

Low
pressure
gas
Quiet Eruptions

Has
basaltic
magma (is
more fluid
and will flow
instead of
explode)
Quiet Eruptions


…and has low
water content
Examples: Hawaii
Typical Hawaiian Eruption
Directed
Reading!!!
Pg. 1–2
Textbook pg. 438
Get out your
Directed
Reading!!!
Pg. 1-2
Find a Checking Pen & Your Volcano Notes!!
Cinder cones
oSmall
base, steep-sided, loosely consolidated
oUp to 1000 feet tall
oLife span of a few years
oCommonly built from gravel size lava rock fragments
called cinders
oViolent eruptions, dangerous when close---High pressure
gas bubbles causes thick lava to explode into the air, lava
begins to cool as it rises and falls becoming very sticky
oWhen lava hits the ground it sticks rather than flows
oThis builds a steep cone with a small base
Cinder Cones:
Shield volcanoes
oLarge
base, gentle slope, lava rock layers
oA few miles high
oLife span of a million years or more
oThe lava is hot, thin, very fluid often basaltic
oExample:
Hawaiian Islands, Iceland
Take a look at these examples:
http://www.volcano.si.edu/world/tpgallery.cfm?category=Shield%20Volcanoes
The Mauna Loa volcano in Hawaii—
the largest volcano on Earth—has
the broad expanse characteristic of
shield volcanoes. It spreads across
half the island of Hawaii.
Shield volcano on Mars;
Taken from space
Shield Volcanoes
Mauna Kea
Composite or strato
Large mountain volcano often snow capped, a
few miles high
Life span of million years or more
Composite or strato
oHave
alternating eruptions of tephra (airborne) and lava. The tephra adds height to the
volcano and the lava cements the tephra
together and adds to the base.
oFound
mostly in subduction zones and have
violent eruptions.
STrato/Composite
aima Volcano, Chile.
Composite (strato) Volcanoes
examples:
Mt. Fuji
Mt. Rainier
Mt. Kilimanjaro
Types of Volcanoes Review
Where do Volcanoes Occur?
Where do Volcanoes Occur?
location
Divergent
Boundaries:
where plates move
APART
Examples
Iceland
Where do Volcanoes Occur?
location
convergent
Boundaries:
where plates come
together
Examples
Cascade range
volcanoes, Andes

Cascade Volcanoes
Where do Volcanoes Occur?
location
Examples
Hot Spots:
plates riding over an
especially hot place
in the mantle
Hawaii, Yellowstone,
Iceland
Hot Spots: Formation of the
Hawaiian Islands
What comes out of volcanoes?
•Lava
•Tephra
•Gases
Lava—3 kinds:
Pahoehoe lava:



Cooler, thicker, slow
moving
harden with a
relatively smooth
surface
Often has a ropy or
wrinkled appearance
Pahoehoe lava:
Aa lava:
• Hot, thin, fast
flowing
• Hardens with a
rough, jagged,
sharp edge
surface
Pillow Lava:
 Lava suddenly cooled by
water
 shows sack-like
segments (stuffed
pillows)
Can you identify the kinds
of lava from the pictures?
Circle your choice.
Tephra

•
•
Basically, rock fragments
Also known as pyroclastic rock
fragments.
There are many different possible
sizes, from very small (volcanic ash
or dust to much larger rocks (called
volcanic bombs)
Ash & dust
Volcanic Bombs
This dacite breadcrust
bomb (about 15 cm in
diameter) was erupted
from the lava dome at
Mount St. Helens,
Washington.
Lahar (mudflow):

mixture of ash, eroded land, and
water flowing down river valleys
Lahar (mudflow):
GASES
water vapor, carbon dioxide,
nitrogen, sulfur dioxide,
hydrogen sulfide, chlorine
Directed
Reading!!!
Pg. 3-5
Textbook pg. 441
Check missing
work board
Get your
volcano Notes &
a Textbook!
Volcano Activity Levels (Stages)
Active (awake):
 Has erupted within recent time and
can erupt again at any time.
Pre-eruption activities:






Increase in earthquake activity under
the cone
increase in temperature of cone,
melting of ice/snow in the crater
swelling of the cone
steam eruptions
minor ash eruptions
Mt St. Helens
Dormant (sleeping):



No eruption within recent times,
but there is record of past
eruptions
Can become active and erupt again
after a “wake up” period
Example: Mt. Rainier
Extinct:
 No eruption within recorded
history
 Not expected to ever erupt again
Example: Mount Mazama (Crater Lake)
Crater Lake
Mount Rainier
• The most dangerous volcano in the US
• The danger is mostly from lahars traveling down
river valleys at a speed of 25mph and destroying
everything in its path
• 100,000 people live on the solidified mudflows of
previous eruptions
Mount Rainier
• The mountain is dangerously unstable, a tall,
steep heap of loose rock held together by the
force of gravity and a cubic mile of glacier ice
that could be melted or shaken loose
• Lahar flows average every 500 years and have
gone as far as the Puget Sound lowlands
• Mount Rainier has erupted 4 times in the last
4000 years with the last eruption 200 years ago
Directed
Reading!!!
Pg. 6-9
Textbook pg. 448
Turn in your
Directed Reading!!!
Pg. 6-9
You have 10 min. to
finish!!!
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