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Unit 4 Chapter 13
Volcanism
There are approximately 485 active volcanoes in the world.
Volcanic eruptions are a major source of some of the most dramatic changes
to the Earth’s surface. Some eruptions are more powerful than
an atomic bomb.
By studying temperature within the earth, scientists can learn more about
the volcanic eruptions.
Formation of Magma
Magma is molten rock under the earth’s surface
Can form under 3 conditions:
1. _______________________________________________________
_______________________________________________________
2. _______________________________________________________
_______________________________________________________
3. _______________________________________________________
_______________________________________________________
Volcanism
Volcanism _______________________________________________. The
melting of the area around the initial movement can melt further adding
more material to the magma.
Lava is _______________________________.
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Volcano______________________________________________________
________________________________________________________
1. Magma chamber 2. Country rock 3. Conduit (pipe) 4. Base 5. Sill 6. Branch pipe
7. Layers of ash emitted by the volcano 8. Flank 9. Layers of lava emitted by the volcano
10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater 15. Ash cloud
Major Volcanic Zones
Most volcanoes are in the area of convergent and divergent zones. A major
zone is the Pacific Ocean. The Ring of Fire encircles this area.
_____________________________
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occur at subduction boundaries thick lava (magma) very gassy,
therefore very, very explosive with a lot of tephra (pyroclastic)
form steep sided volcanoes with a lot of activity
Most famous volcanoes
Mt St Helen's & Mt Vesuvius
The Aleutian Islands, island arcs, by the North Pacific Ocean,
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__________________________________
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Long narrow fractures in oceans or on land with the loargest
amount of magma
Basaltic lava with only few gases smooth easily flowing lava
found in spreading centers (division boundaries)
Mid Atlantic Ridge
_________________________________
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Volcano not at a plate boundary
Smooth basaltic lava - non gassy - very hot
forms large volcanic rises under water until it is big enough to
rise above the surface
Hot spots do not move, the plate moves over the hot spot
Ex. Hawaii
Intrusive Activity
Since magma is less dense than rock will push upward and intrude into the
overlaying rock. This can cause it to change (Metamorphic),
melt or even crack the surrounding area.
Sometimes the magma will cool or solidify without erupting. This will harden
within the volcano.
After some time, the surrounding
sedimentary rock will erode away leaving the igneous intrusion
called a ___________________________.
Devils Tower, Wyoming
Section 2 Volcanic Eruptions
Volcanoes are windows into Earth’s interior. Lava can provide a look into
what is inside the earth. There are two types of magma/lava,
_______________________________________.
Rhyolitic (Felsic)
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a. ___________________________________
b. ___________________________________
c. Light colored
d. Usually associated with explosions
e. Lowest melting point
f. by Continental Hot Spots (Yellowstone Caldera)
Basaltic Magma (Mafic)
a. _________________________________
b. _________________________________
c. Dark colored
d. Highest melting point
e. Rarely explosive
f. by Rifts, oceanic hot spots (Hawaii)
Types of Eruptions
Viscosity
__________________________________. Magma high in silica resists flow,
low in silica flow very fast.
Magma contains many gases – H2O, CO2, SO2 , H2 , H2S (Hydrogen Sulfide)
Very gassy - _____________________________________
No gas - ________________________________________
Quiet Eruptions
Oceanic eruptions are among the quietest eruptions. That is because they
are made from mafic magma which has a low viscosity. Not explosive.
Lava Flows
Aa - _____________________________________
Pahoehoe - ______________________________________________
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Blocky lava – __________________________________________________
____________________________________________________
Explosive Eruptions
Pyroclastic materials
It is ___________________________________________________. It
can be explosive and it can be mild. It contains super heated
gases, ash and other objects that are ejected from the opening.
Pyroclastic flow:
_________________________________________________________
________________________________
Types of Pyroclastic Material
Pyroclastic material is classified by size.
The solid fragments are also called tephra.
1. ________________________________
2. ________________________________
_____________________________
_____________________________
3. _______________________________________________________
4. ________________________________
Fast moving mud flow from melting snow and ice mixing
with loose gravel.
Types of Volcanoes
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There are 3 main types of volcanic cones that can be produced by a
volcano.
___________________
a. Broad base
b. Cooled lava layers because of low viscosity; less explosive
c. Mauna Loa, Hawaii – 4170ft above sea level, base is 5000ft below sea
level.
________________________
a. Molten lava spewed from a vent piled up
b. Smallest of the volcanoes, formed by larger ones
c. Slope angle can be as much as 40%
__________________________
a. Alternating layers from the eruptions pile up around a vent
b. Violent eruptions
c. Can lay dormant for a long time until it needs to relieve pressure
again.
d. Mount St. Helen’s is called a stratovolcano because of its size.
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Other unique volcanic features:
Lava Plateau (Dome)
This is not a normal dome mountain. This happens when lava comes
up from a crack in the ground. It can spread on the surface making a layer
of basalt on top. This can cover large areas.
Columnar jointing
Are unique six sided columns that are formed when basaltic lava cools
& cracks, you know, the internal arrangement of its atoms. You can find this
anywhere, Iceland, New York, California, etc.
Devils Post Pile State Park, Ca
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Calderas
A cone forms from an eruption. The magma beneath a volcano is released
than the top of a volcano collapses in. A large crater is formed which can
later fill with water.
Mount Mazama in Oregon filled with water after its collapse and is now called
Crater Lake.
Predicting Volcanic Eruptions
Scientists study the eruptions to see if there are patterns to help predict
eruptions.
Earthquake Activity
Warning signs of an eruption. Earthquakes usually precede an eruption.
Patterns in Activity
Before an eruption there may be an upward movement of magma, causing a
swelling of the outer area. Scientists look for the history of a volcano to help
them try to predict when it may erupt again. A dormant volcano can erupt
again.
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Other Volcano Information
Extraterrestrial Volcanoes
1.
Moon
a. Evidence of volcanoes are the dark spots which is mostly
basalt
b. Evidence is also there because we can see volcanic formations
2.
Mars
a. Has a number of shield volcanoes
b. Olympus Mons – largest known volcano in the solar system
c. 1999 Mars Global Surveyor saw lava flows only 20-60 million
years old.
3.
Venus
a. Has about 1600 large volcanoes
b. Scientist feel that the volcanic activity is causing the heavy
thick atmosphere
4.
Io
a. Most volcanically active place in the solar system
b. Very active today
History:
1.
Krakatoa - Indonesia 1883
Most violent eruption in historic times
Loudest natural sound ever heard (1900 miles)
blew away 1/2 an island
broke windows 90 miles away
36,000 people died
2.
Vesuvius - 79 AD
Pompeii was buried under 30 feet of ash - everyone died
3.
Mt Popocatepetl (Mt. Popo) - current