Transcript Volcanoes - schmidtsciencepage

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
1.
2.
3.
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