How the formation of Volcanoes takes place?

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Volcanoes are formed when one tectonic plate moves over another. A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and most are found underwater.
1. Section 3.2-3.3
2. What is a volcano?
• Volcano: an opening in Earth’s
crust through which molten
rock, rock fragments, and hot
gases erupt.
– Magma vs. lava: remember the
3. DIAGRAM THIS-pg. 87 has a similar but untitled diagram
4. Where do volcanoes occur?
Most form along plate boundaries ….
1. in subduction zones (one plate sinks
under another)
2. over hot spots
3. where plates are pulling apart
5. See page 89
6. What determines how explosive an eruption
1. Water Vapor:
Vapor more water=bigger explosion
2. Trapped gases (water and CO2):
– Easy escape (low pressure)=quiet eruption
– Difficult to escape (high pressure)=explosive/violent
3. Magma Type:
– Balastic (thin) =quiet eruption
– Granitic/Andestic (thick)=violent eruption
**NOTE: A Pyroclastic flow is a fast moving mixture of
water, gases and ash that can be deadly
7. Magma Composition
the same (pa-HOY-hoy)
•If pahoehoe
As lava flows at a
lower structures shaped
a stiff,
lava cools, it
like tubes,
slowly forms
movingballoons,a or lava
aa (AH-ah) • Volcanoes with basaltic
ropelike . pillow lava produce:
lava formations
8. Magma Composition
• You can find volcanoes
with basaltic lava
– Hawaiian Volcanoes,
• Kilauea
• Mona Loa
– Iceland
• Heimaey
• Hekla
9. Magma Composition
Granitic Lava
“If it had erupted in a populated
area…"The magnitude of the • Some examples of granitic
eruption can perhaps be best
realized if one could imagine a volcanoes are
similar outburst centered in New – Yellowstone Caldera
York City. All of Greater New York • It is a super voclano!
would be buried under from ten to
fifteen feet of ash; Philadelphia – Katmai, Alaska
would be covered by a foot of gray • Last eruted in 1912.
ash and would be in total darkness
for sixty hours; Washington and
Buffalo would receive a quarter of
an inch of ash, with a shorter period
of darkness. The sound of the
explosion would be heard in Atlanta
and St. Louis, and the fumes noticed
as far away as Denver, San Antonio,
and Jamaica."
10. Magma Composition
Andesitic Lava
Mount Pelee, Martinique
– Famous for the May 8, 1902 eruption
which killed 29,000 people and
destroyed the city of St. Pierre. This is
the largest number of causalities for a
volcanic eruption this century.
• Mayon, Phillipines
– It is the most active volcano in the
Philippines. Since 1616, Mayon has
erupted 47 times.
– It’s 1814 eruption killed 1,600.
12. 3 Basic Volcano shapes
The shape and size are determined
by the type of magma feeding it.
Pg. 90-91
13. 1. Shield Volcano
• Formed by quiet eruptions
• Slow-moving lava flows
• Basaltic lava builds up in flat layers
• Largest with gently sloping sides
• Ex: Mauna Kea-Hawaiian Islands
14. Example of Shield Volcano
• Mauna Loa
• Mt. Kilauea
– Probably one of the
world’s most active
– The eruption of Kilauea
Volcano that began in
1983 continues at the
cinder-and-spatter cone
of Pu`u `O`o
Mt. Kilauea
Picture from
15. 2. Cinder Cone Volcano
• Caused by explosive
• Granitic lava thrown
high into the air
• Lava cools into
different sizes of
volcanic material
called tephra
• Steep-sided, loose
17. Example
Cinder Cone Volcano
• Parícutin Volcano
in Mexico is a
great example of
a cinder cone
18. Paracútin
• On February 20, 1943, a Mexican
farmer noticed that a hole in his
cornfield that had been there for as
long as he could remember was
giving off smoke.
• Throughout the night, hot glowing
cinders were thrown high into the
• In just a few days, a cinder cone
several hundred meters high
covered his cornfield.
19. 3. Composite Volcano
• A mix of the other two types
• Quiet or violent
• Basaltic or granitic
• Steep or gentle slopes
• Layered of tephra
21. Example of
Composite Volcano
• Mount St. Helen’s
– Erupted in 1980
– 57 fatalities
– Over 7000 big game animals
– 4 billion board feet of timber (enough
to build about 300,000 two-bedroom
homes) destroyed
– Destroyed 27 bridges, nearly 200
homes. Blast and lahars destroyed
more than 185 miles of highways
and roads and 15 miles of railways.
22. Example of
Composite Volcano
• Mount Pinatubo
– Erupted in 1991
– Killed 847 people
– 184 people injured
– 10, 000 home destroyed and
another 5,000 were damaged.
– The ash cloud took one year to
spread around the globe,
reducing global temperatures.
This resulted in
• Floods in 1993 along the
Mississippi River
• Drought in Africa in 1993
• The US had its 3rd wettest &
coldest winter on record.
23. Example of
Composite Volcano
• Krakatau
– One of the most violent
eruptions in recent
times occurred on an
island in the Sunda
Straits near Indonesia
in August of 1883.
– Krakatau, a volcano on
the island, erupted with
such force that the
island disappeared.
24. Example of Composite Volcano
• Killed 36,000 people most
were killed by a giant
• Destroyed 160 villages
• Fine ashes from the eruption
were carried by upper level
winds as far away as New
York City
• Volcanic dust lowered global
temperatures for five years,
this caused
25. Scientists monitor volcanoes.
• Scientists monitor volcanoes to look for
warning signs that an eruption may be
coming. Warning signs include:
– Earthquakes
– Changes in the tilt of the ground
– Rising temperatures of openings
– Changes in volcanic gases being tested.
26. Both shield and composite volcanoes can form features called calderas, a huge
crater formed by the collapse of the volcano when magma rapidly erupts from
underneath it.
27. Volcanoes Affect Earth’s
Land, Air, and Water
28. Materials From Volcanic Eruptions Affect Earth
Land Air Water
Lava Poisonous Gases* Hot Springs
Volcanic Ash* Adds to Acid Rain Geysers
Landslides (can Haze Fumaroles
cause tsunamis)
Mudflows Lower Deep –Sea Vents
*These can get in the jet stream and affect the weather around the
world for months or years
**There NOW
can be PLEASE
benefits: richer farmland and beautiful landscapes
29. See page 97
30. 2.4 million and 640,
000 years ago
31. See page 101
32. Fumarole
33. Deep-Sea Vent
Hot Spring
34. G. Life Cycle of a Volcano
1. Active- one that is erupting or has shown
signs that it may erupt in the near future
2. Dormant- volcano to awaken in the
future and become active
3. Extinct-dead volcano; not likely to erupt
35. Mt. Saint Helens
36. Resources used
• Volcano World
• US Geologic Survey
• Glencoe Earth Materials &
• McGraw-Hill Changing Earth