December 10, 2012
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Sponge: Update Table of Contents
124 Directed Reading
125 Earthquakes info sheet
126 Study guide for Final Exam
127 Volcanoes notes
128 Volcanoes notes (cont’d)
129 Volcanoes “Case Studies” notes
• I will hand back the quizzes and go over them in a moment.
Volcanoes
1. Brainpop
• Before you start on this
Power Point, watch the
Brainpop about
Volcanoes and take the
“Graded Quiz”.
• www.brainpop.com
• User name: webbbridge
• Password: wbms
Vulcan, Roman God of Fire
• The word volcano
comes from name of
the roman god of fire,
Vulcan.
2. What is a Volcano?
• A volcano is a place on the
surface where molten rock,
gases and pyroclastic debris
erupt through weak spots in
the earth's crust.
• Volcanoes vary quite a bit
in their structure - some are
cracks in the earth's crust
where lava erupts, and
some are domes, shields, or
mountain-like structures
with a crater at the summit.
3. Magma or Lava?
• Magma is a molten mixture
of rock forming substances
(liquid rock), gases, and
water vapor.
• When it reaches the surface
it is called lava.
• It forms igneous rock when
it cools.
• 4. Reshapes the surface by
adding to land, creating
mountains and islands.
5. Location of Volcanoes
• Most occur on diverging plate boundaries or in
subduction zones at converging boundaries.
• About 600 active volcanoes on land, and more
under the ocean.
Mid-ocean Ridges
• Underwater rift valleys
where new crust is
being created from lava
pouring out of cracks in
the ocean floor.
• Only in a few places like
Iceland and the Azores
do they rise above the
ocean surface.
• Divergent Boundaries
• Worlds longest
mountain range is the
Mid-Atlantic Ridge
World Wide Mountain Range
Mid-Ocean
Ridges
• Subduction can cause a series of volcanoes parallel to the
plate boundary.
• This creates mountain ranges like the Andes and
volcanoes in the Pacific Northwest.
• At sea they create island arcs like Japan.
6. The Ring of Fire
• A large number of volcanoes lie directly on tectonic plate boundaries.
In fact, the plate boundaries surrounding the Pacific Ocean have so
many volcanoes that the area is called the Ring of Fire.
7. Hot Spots
Hot spots are
volcanically active
places on the Earth’s
surface that are far from
plate boundaries.
More rarely, volcanoes are found in the middle of
plates. Most of these volcanoes occur within
oceanic plates. The Yellowstone volcano is doubly
rare, because it is found in the middle of a
continental plate.
This map shows selected hotspots throughout the
world. It is believed that more than 100 such
hotspots have been active during the past 10 million
years
Hot Spot Volcanoes
• Can occur in the middle
of plates.
• The plate moves over a
stationary hot spot.
• A chain of islands is
formed over millions of
years as the plate drifts
over the hot spot.
Yellowstone Hot Spot
8. Magma and the Earth’s Surface
• Magma rises because it
is less dense than the
surrounding solid
material.
• It will rise to the surface
unless it is trapped
beneath layers of rock.
A Volcano Erupts
• When a volcano erupts,
the dissolved gases
(carbon dioxide and
water vapor mainly)
rush to the surface,
carrying the magma
with it,
• At the surface the
magma becomes lava.
Exploring a Volcano
Cross section of a volcano
Magma Chamber
• A large underground
pocket formed by the
rising magma.
Pipe
Side Vent
• Sometimes lava will exit
from cracks in the side
of a volcano.
Pipe
• Narrow, almost vertical
crack in the crust that
carries the magma to
the surface.
• Note: The “pipe” is
sometimes called a
“vent”.
Vent
• Point on surface where
the magma leaves the
pipe.
Crater
• Bowl shaped area that
forms around the vent.
• Crater Lake in Oregan
was formed when
Mount Mazama blew its
top some 8,000 years
ago.
Lava Flow
• The river of lava that
gravity causes to flow
down the side of a
volcano
9. Viscosity
• Is the resistance a liquid
has to flowing.
• Honey has a high
viscosity as it pours very
slowly.
• Water has a low
viscosity as it pours
quickly.
Magma
• Silica in Magma
• The two most abundant elements in earth's crust and mantle
are oxygen and silicon. These two elements combine to form
the molecule called silica. (Note that silicon is an element,
while silica is a molecule). The formula for silica is:
• SiO2
Magma with a low silica content = runny lava (low
viscosity). These are quiet eruptions (non-explosive).
Magma with high silica content = thick lava (high viscosity).
These are explosive eruptions.
• 11. IMPORTANT:**The higher the silica content of a
magma, the higher the viscosity (thickness) and
more explosive the eruption will be.**
HIGH
Cinder Cone
Volcano
Shield Volcano
LOW
Silica content
Viscosity
Violence of eruption
Composite
Volcano
*Also, the
more dissolved
gases a
volcano has,
the more
explosive the
eruption.
12. Quiet Eruptions
• Type of eruption
is determined by
the amount of
gas and the
viscosity of the
magma.
• Low pressure gas
and low viscosity
magma will ooze
out, forming
shield volcanoes.
12. Explosive Eruptions
• Thick magma can plug
the volcano pipe like a
cork.
• The pressure can build
until it suddenly
explodes.
• The higher the gas
content the larger the
explosion.
Volcanic Material
• Rock fragments thrown into
the air are called tephra.
• They are classified by size.
• Dust is the smallest,
followed by ash.
• Larger pieces are called
lapilli, which means “little
stones.” Also called cinders.
• Bombs/blocks: The largest
tephra thrown from a
volcano can be the size of a
car or small building. Bombs
cool on the way down.
Pyroclastic Flows
• Very deadly cloud of
ash, gas, dust, and
other tephra that
rushes down the sides
of a volcano at speeds
of nearly 200-km/hr.
• Temperature can
exceed 700°C.
13.Active Volcanoes
• One that is currently erupting or
may erupt in the very near future.
• Sakurajima is one of the most
active volcanoes on Earth. Since
764 AD eleven eruptions have
caused fatalities. The largest
historic eruption was in 1471-1476
and caused an unknown number
of deaths, probably from
pyroclastic flows. An eruption in
1779 caused 153 deaths from
tsunami and tephra. Evacuation of
the island in 1914 prevent a larger
death toll from that eruption. The
current eruptive activity began in
1955.
Dormant Volcanoes
• Sleeping volcano.
Expected to erupt again
in the future.
• Can be thousands of
years between
eruptions.
Extinct Volcanoes
• A dead volcano, not
considered likely to ever
erupt again.
14. There are 3 basic types of volcanoes
• Shield
• Cinder Cone
• Composite (also called strato volcanoes)
Shield Volcanoes
• Built by repeated lava flows
from quiet (nonexplosive)eruptions.
• Builds up a gently sloping
volcanic mountain.
• Lava is very runny and
spreads out over a large
area.
• Very large.
• Ex: Hawaiian Islands
Cinder Cone Volcanoes
• Erupt explosively,
forming, the cinders
pile up around the vent.
• This forms steep, cone
shaped volcanoes.
• Tend to be very small.
• Ex: Paricutin in Mexico
Composite Volcanoes
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Also called stratovolcanoes
Most common type
Has alternating layers of ash
and lava.
Form from explosive
eruptions of pyroclastic
material followed by quieter
eruptions of lava. (It’s kind
of a cross between shield
and cinder cone volcanoes.)
Ex: Japan’s Mt. Fuji. In the
United States: Mt. Ranier in
Washington state, and Mt. St.
Helens.
More info about Types of Volcanoes
• http://www.ruf.rice.edu/~leeman/volcanotyp
e_poster.gif
Landforms from Magma
• When magma cools it
hardens to solid rock.
• Igneous rock is usually
fairly hard, so when the
softer rock and soil
around it erodes, these
landforms are exposed
to view.
Volcanic Necks
• When the magma in
the volcano pipe
hardens it forms a
volcanic neck.
• It looks like a giant
tooth sticking out of
the ground when the
softer rock around it
erodes away.
Dikes
• Magma that forces itself
across rock layers is
called a dike.
• Tend to be vertical
Sills
• Magma that squeezes
between layers of rock
before hardening forms
sills.
• Usually horizontal
Batholiths
• Very large rock masses
that form the core of
some mountain ranges.
• Occurs when a large
amount of magma cools
below the surface.
• Stone Mountain in
Georgia
Volcanoes and Climate Change
The explosion of Mount Tambora in 1815 blanketed most of Indonesia in darkness
for three days. It is estimated that 12,000 people died directly from the explosion
and 80,000 people died from the resulting hunger and disease. The global effects
of the eruption were not felt until the next year, however. During large-scale
eruptions, enormous amounts of volcanic ash and gases are ejected into the
upper atmosphere.
As volcanic ash and gases spread throughout the atmosphere, they can block
enough sunlight to cause global temperatures to drop. The Tambora eruption
affected the global climate enough to cause food shortages in North America and
Europe.
Later, come back to this slide and read about it here to see why 1816 was called
“The Year with No Summer” (Note: do this only when you are finished with your
notes).
http://www.britannica.com/EBchecked/topic/581878/Mount-Tambora
The Year Without Summer
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Volcanic ash caused global temperatures
to fall by over 1.2 degrees Celsius .
Acted as a “sun filter.”
Weather patterns were chaotic for years
and temperatures did not return to normal
until 1888.
In the US 1816 was the “Year without
Summer,” as frost in May and snow in
June destroyed the crops in New England.
Caused famine and death from disease
throughout the world.
Mount Pinatubo
• More recently, the eruption of Mount Pinatubo, June 15,
1991, caused average global temperatures to drop by as much
as 0.5°C. Although this may seem insignificant, such a shift can
disrupt climates all over the world.
• The eruption column of
Mount Pinatubo on
June 12, 1991, three
days before the
climactic eruption.
Case Studies- Volcanic Eruptions in History
• Visit the National Geographic Website. Click
on the “Case Studies” tab. Write down each
of the volcanic eruptions and facts about each
one. (Do this on the next page of your
composition notebook).
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http://environment.nationalgeographic.com/environment/natural-disasters/forces-of-nature/
National Geographic Website
• Make your own volcano! (by Manipulating the
silica content and amount of dissolved gases)
• http://environment.nationalgeographic.com/environment/naturaldisasters/forces-of-nature/