3. VOLCANISM? Sounds familiar!
Volcanism is the eruption of molten rock (magma) onto the
surface of a planet. A volcano is the vent through which magma
and gases are discharged. Magma that reaches the surface is
called lava. Volcanos are named for Vulcan the Roman god of
fire!
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VOLCANISM: Its Features
4. LET’S PUSH THESE!
How do volcanoes form?
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VOLCANISM: Its Features
What causes volcanoes to erupt?
Where do most volcanoes occur?
What are the different types of volcanoes?
What determines the degree of violence associated
with volcanic activity?
5. Ah! Yes, let’s define the
terms…
A volcano is a vent or opening
on planet’s surface which allows
molten rock called
magma, volcanic ash and gas to
escape out onto its surface. A
volcano gives a look like a
mountain from which lava
erupts. The hot magma erupting
from a volcano is called lava.
KNOWLEDGE ERUPTION!
Definition of Terms
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VOLCANISM: Its Features
6. Most volcanoes are formed by the movement of tectonic plates on the
surface of the earth. These plates are basically huge pieces of rock that ‘float’
on the mantle (a layer of the earth that is sort-of liquid rock).
KNOWLEDGE ERUPTION!
How Volcanoes Form
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TECTONIC
PLATES
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VOLCANISM: Its Features
7. KNOWLEDGE ERUPTION!
Origin of Volcanoes
1. Magma rises
2. As the magma rises it melts gaps in the
surrounding rock
3. As more magma rises a large reservoir
4.Pressure from the surrounding rock causes the
magma to blast
5. The magma, now called lava,
builds up at the vent forming a
volcano.
6.Often the volcano sides will be
higher than the vent forming a
depression called a crater
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VOLCANISM: Its Features
8. KNOWLEDGE ERUPTION!
What Causes Volcanoes to Erupt?
TECTONIC PLATES
AND SETTINGS
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Subducting Plate Margins
Spreading Plate Margins
Intraplate
(Hotspot)
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VOLCANISM: Its Features
9. Again, it’s in the edge of
TECTONIC PLATES.
KNOWLEDGE ERUPTION!
Areas Where Most Volcanoes Occur
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VOLCANISM: Its Features
10. KNOWLEDGE ERUPTION!
Areas Where Most Volcanoes Occur
The Pacific Ring of Fire
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-It is a string of volcanoes and
sites of seismic activity around
the edges of the Pacific Ocean.
-It isn’t quite a circular ring. It
is shaped more like a 40,000-
kilometer (25,000-
mile) horseshoe.
-A string of 452 volcanoes.
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VOLCANISM: Its Features
11. KNOWLEDGE ERUPTION!
What determines the degree of violence associated
with volcanic activity?
Magma – molten rock or liquid that is mostly silica
Lava – solidified magma
Pyroclasts – from the Greek pyro, “fire”, and clast “broken”
– rock fragments (pyroclastic debris is also called tephra)
Lava flows – fissures in the ground
Extrusive rock - surface rock resulting from volcanic activity (rock
formed by solidification of lava)
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VOLCANISM: Its Features
12. KNOWLEDGE ERUPTION!
What determines the degree of violence associated
with volcanic activity?
Crater – funnel shaped pit at the
top of a volcano. formed when
material is blown out of the
volcano by explosions
Caldera – when the volcano
collapses due to an empty
magma chamber
CRA
TER
CALDERA
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VOLCANISM: Its Features
13. KNOWLEDGE ERUPTION!
What determines the degree of violence associated
with volcanic activity?
DEVELOPMENT
OF A CRATER
LAKE
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VOLCANISM: Its Features
14. KNOWLEDGE ERUPTION!
What determines the degree of violence associated
with volcanic activity?
PHYSICAL Whether eruptions are very explosive or
CHARACTERISTICS relatively "quiet" is largely determined by two
OF LAVA factors:
(1) the amount of gas in the lava or magma
(2)the ease or difficulty with which the gas
can escape to the atmosphere
Viscosity – resistance to flow
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VOLCANISM: Its Features
15. KNOWLEDGE ERUPTION!
What determines the degree of violence associated
with volcanic activity?
Felsic
Contains more than
65% Silica
TYPES OF LAVA
Mafic
Silica (Poor) (45-52%)
Rholite
Basalt
Andesite
Intermediate
Silica
Composition
(53-65%)
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VOLCANISM: Its Features
16. What determines the degree of violence associated
with volcanic activity?
The two most
important factors that
influence viscosity are
the
(1) temperature of the
lava relative to the
cooler temperature
which it solidifies
(2) the silica (Si𝑂2
content of the lava)
KNOWLEDGE ERUPTION!
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VOLCANISM: Its Features
17. KNOWLEDGE ERUPTION!
Types of Volcano
Composite
Volcanoes
Composite volcanoes
often form the largest
and tallest volcanoes.
They are the most
explosive and dangerous
of the types of volcanoes.
Mt. Saint Helens in Washington state.
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18. KNOWLEDGE ERUPTION!
Types of Volcano
Cinder Cone
Volcanoes
Usually smaller in size
than composite
volcanoes, and the
eruptions are smaller
also. They form into steep
cone shaped hills.
Paricutin in Mexico
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19. KNOWLEDGE ERUPTION!
Types of Volcano
Shield
Volcanoes
Shield volcanoes do not
erupt or explode like
composite or cinder cone
volcanoes. Shield
volcanoes have much
smaller eruptions
producing less ash.
Muana Loa in Hawaii.
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20. KNOWLEDGE ERUPTION!
Pyroclastic flow descending Mayon volcano, Philippines.
-Most of the gas released during
eruption is water vapor
-Carbon dioxide, sulfur dioxide,
hydrogen sulfide, and hydrochloric acid,
are given off in lesser amounts
-Surface water introduced into a
volcanic system can greatly increase the
explositivity of an eruption.
-At high altitudes, the pyroclastics often spread out into a dark, mushroom cloud. The fine
particles are transported downwind by high atmosphere winds. Eventually debris settles
back to earth under gravity's influence as ashfall (or sometimes pumicefili) deposits.
A pyroclastic flow is a mixture of gas and pyroclastic debris that is so dense that it hugs the
ground as it flows rapidly into low areas.
Gases and Pyroclastics
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VOLCANISM: Its Features
21. KNOWLEDGE ERUPTION!
Types of Volcanic Eruptions
Hawaiian Eruption
In a Hawaiian eruption, fluid lava is ejected from a
vent as fire fountains or lava flows. The 1969 eruption
at Mauna Ulu, a vent of Kilauea Volcano in Hawaii,
was a spectacular example of fire fountaining. Photo
by D.A. Swanson, USGS, August 22, 1969.
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VOLCANISM: Its Features
22. KNOWLEDGE ERUPTION!
Types of Volcanic Eruptions
Short bursts of glowing lava,
created from the bursting of
large gas bubbles at the
summit vent of a volcano typify
a Strombolian eruption. This
photo, taken from the summit
of Stromboli, a volcano in the
Aeolian Islands, Italy, shows a
classic example of this activity.
Photo by Andrew Hague,
Istockphoto.com.
Strombolian Eruption
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VOLCANISM: Its Features
23. KNOWLEDGE ERUPTION!
Types of Volcanic Eruptions
Vulcanian
Eruption
Relatively small but violent
explosions of viscous lava create
columns of ash and gas and
occasional pyroclastic flows, as
seen at this eruption of the
Santiaguito volcanic dome
complex in Guatemala. Photo by
Jessica Ball, March 15, 2009.
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VOLCANISM: Its Features
24. KNOWLEDGE ERUPTION!
Types of Volcanic Eruptions
Plinian Eruption
The largest and most violent of all explosive
eruptions, Plinian eruptions send columns of
pulverized rock, ash, and gases that rise miles
into the atmosphere in a matter of minutes.
Mount St. Helens in Washington State
experienced a Plinian eruption following a major
flank collapse in 1980. Photo by Austin Post,
USGS, May 18, 1980.
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VOLCANISM: Its Features
25. KNOWLEDGE ERUPTION!
Types of Volcanic Eruptions
Lava Dome
Lava domes, such as this example in
the crater of Mount St. Helens, are
piles of viscous lava that are too cool
and sticky to flow far. Domes grow and
collapse in cycles, and often form at
volcanoes that also experience Plinian
eruptions. Photo by Lyn Topinka,
USGS, August 12, 1985.
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VOLCANISM: Its Features
26. KNOWLEDGE ERUPTION!
Types of Volcanic Eruptions
Lava erupting through water
creates the dramatic plumes
of scoria and billowing ash-
and-gas clouds of a
Surtseyan eruption. The type
example of this eruption
occurred at Surtsey, a
volcanic island off the coast
of Iceland. NOAA image of
the 1963 eruption.
Surtseyan Eruption
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VOLCANISM: Its Features
27. KNOWLEDGE ERUPTION!
Types of Lava Flow
A smooth and continuous
lava crust. Pahoehoe forms
when the effusion rate is
low and consequently the
velocity of lava flow is slow.
Pahoehoe lava flow is
usually at least 10 times
slower than typical aa lava
flow.
Pahoehoe
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VOLCANISM: Its Features
28. KNOWLEDGE ERUPTION!
Types of Lava Flow
Aa lava is a rough rubbly
crust of a lava flow. It is a
major lava flow type.
Aa
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VOLCANISM: Its Features
29. KNOWLEDGE ERUPTION!
Types of Lava Flow
A distinctive lava flow morphology
that has been appearing in our
dredges is pillow lava. Pillow lavas
form when hot lava flows into water
and cools rapidly, creating long
tubes and bulbous pillow-shaped
mounds of rock. Pillow lavas are
found not only in the ocean but
also under glaciers that overlie
volcanoes.
Pillow Lava
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VOLCANISM: Its Features
30. KNOWLEDGE ERUPTION!
Types of Lava Flow
Blocky flows are
common if the silica
content of lavas is
higher (composition
of basaltic andesite to
rhyolite).
Blocky
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31. KNOWLEDGE ERUPTION!
Three Definitions of Volcanoes
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