Volcanoes
What is a volcano?
• An opening in the earth's crust through which
molten lava, ash, and gases are ejected.
• The opening in Earth’s surface which allows
material to escape is called a vent.
How do Volcanoes form?
• Volcanoes form when molten rock from the
mantle rises and leaks into the crust.
• The molten rock, called magma, rising from
the mantle, gathers in a reservoir called the
magma chamber.
• Eventually, but not always, the magma erupts
onto the surface and forms lava.
Formation of a Volcano
This is a drawing of magma making it's way up
through the crust, causing the volcano to expand
prior to eruption.
Where do Volcanoes form?
• At a Subduction Zone
• Along Hot Spots/plumes
• Along Divergent Plate Boundaries
What is Hot Spot?
• An area in the middle of a lithospheric plate where
magma rises from the mantle and causes eruptions at
the Earth's surface.
• If the hot spot forces magma to the surface during an
eruption, it may create a volcano.
• Continual eruptions could eventually build a whole
island on the surface. (Ex. Hawaii)
• The hot spot is stationary and the plate moves over it.
Hot spots cont……
• Hot spots may cause the formation of geysers
or hot springs, rather than lava based
eruptions.
Hot Spot
Yellowstone Hot Spot
• Over the past 2 million years, the Yellowstone
supervolcano has erupted every 600,000
years.
• It was 640,000 years ago when it last
exploded. Another eruption, geologically
speaking, is therefore threatening.
• Five miles beneath Yellowstone, lies an
immense pool of red hot magma
• Fed from the Earth’s mantle, it has been
growing.
• This reservoir of magma and gas is now 31
miles long, 19 miles wide and 6 miles deep.
• The Yellowstone “hot spot” is considered to
be the foundation of a rare “supervolcano”
• It is estimated that a supervolcano would
erupt with the power at least 1000 times
greater than an ordinary volcano.
Typical Volcano Structure
Types of Volcanic Eruptions
• Explosive: Short, violent eruptions that break
lava into smaller pieces (cinders and ash)
• Effusive: Slow, continual eruptions of lava
Categories for Volcanoes
• Active
– Has erupted in the last 100 years
• Dormant
– Has erupted in the last 1000 years and is expected
to erupt again
• Extinct
– Hasn’t erupted in over 1000 years and is not
expected to erupt again
Types of Volcanic Hazards
• Lava: Molten rock above the surface of
Earth/exposed to oxygen
• Three categories based on characteristics:
• Aa
• Pahoehoe
• Pillow
1. Lava--Pahoehoe
• Lava that has a smooth, ropy surface.
• Typically thin, slow moving lava (150 ft/hr)
• Cools as a smooth, glassy surface
Pahoehoe
Pahoehoe
2. Lava-Aa
•
•
•
•
Rigid, spiky lava
Fast cooling, viscous (thick)
Can moves as fast as 30 miles/hr
Rough surface after cooling
Lava-Aa
Aa lava
3. Pillow Lava
• Lava is released under water
• Thick, slow moving eruptions
• Cold sea water rapidly solidifies lava into
round, pillow-like shapes
Pillow Lava
Tephra
• Solid material that is ejected from the volcano
; particle size decreases as distance from
volcano increases
• Ex. Cinders, ash, bomb
• Damage can include: lightening, respiratory
problems, interference with aircraft,
destruction of vegetation, building collapse
Tephra
Gases
Poisonous Gases
• Gas developed as magma heats water vapor
• Chemicals are dissolved in water and evaporated
as gas due to high temperatures
• Typical gases released: Carbon Dioxide, Sulfur
Dioxide, Carbon Monoxide, Hydrochloric Acid
• May indicate impending eruption
• Poisonous in large amounts or to small creatures
Pyroclastic Flow
What is it?
– Fluidized masses of rock fragments and gases that
move rapidly in response to gravity
Facts:
– Avalanche of material (gas/rock/debris) with very high
temperature.
Hazards:
– Pyroclastic flows can incinerate , bury, and/or
asphyxiate people.
– Localized danger (if you are not in the path of the
avalanche than you are not in danger)
Pyroclastic Flow
Lahar
• What is it?
– Debris avalanches that contain water from snow
and ice that melt and mix with loose debris
• Facts:
– Can cause massive flooding along waterways
– More widespread than pyroclastic flow
• Extremely dangerous for people living close to
a volcanic eruption or near water associated
with volcano
Lahar
Lahar
Vocabulary
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4.
5.
6.
7.
Volcano
Vent
Magma
Magma Chamber
Lava
Subduction Zone
Hot Spot
8. Aa Lava
9. Pahoehoe Lava
10. Pillow Lava
11. Tephra
12. Pyroclastic Flow
13. Lahar
Types of Volcanoes
• Composite/StratoVolcanoes
• Formed by Alternating layers of lava and ash
• Typically steep sided and have a high
elevation.
• Explosive Eruptions
• Ex. Mount Fuji, Japan
Mount St. Helens, WA
Types of Volcanoes cont…..
• Shield Volcanoes
• Formed by continuous eruption of lava over
long periods of time.
• Usually very large at the base and not very
steep.
• Effusive eruptions
• Ex. Mauna Loa and Kilauea in Hawaii
Example of Shield Volcano
Types of Volcanoes
• Cindercone
• Formed from the eruption of lava fragments
called cinders.
• Usually form quite rapidly and are tall and
steep sided.
• Not as tall as Strato and not as wide as Shield
• Ex. Mount Paricutin in Mexico
Cindercone