Download VOLCANOES MR.OCHOA CHAPTER 6

VOLCANOES
CHAPTER 3
OBJECTIVE AND STARTER
•
Objective: Today you will learn about volcanoes and
why they form.
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Starter-KWL Chart
K(What you Know about
Volcanoes
W (What you want to learn about
Volcanoes)
L (What you learned about
volcanoes)
Background Information
•
Have you ever seen a
volcano? What was
happening?
•
Iceland at Night
Volcano
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A weak spot in the crust
where molten material
comes to the surface.
Where are they found?
Ring of Fire
A major volcanic belt
formed by many volcanoes
that rim the Pacific Ocean
is known as the Ring of
Fire.
Volcanoes occur at three places:
DIVERGING PLATE BOUNDARIES
SUBDUCTION ZONES
HOT SPOTS
Divergent Boundaries can form volcanoes
at the mid-ocean ridge. Lava pours out of cracks in the ocean
floor. Most volcanoes at the mid-ocean ridge do not rise
above the ocean’s surface!
Many volcanoes form near converging plate
boundaries where oceanic crust returns to the mantle.
Slabs of oceanic crust sink through a deep ocean
trench into the mantle, where it forms magma that
rises back toward the surface.
Island Arc
Volcanoes at boundaries where two oceanic plates collide create a curved string
of islands called a(n) island arc. Three major island arcs include Japan, New
Zealand, Indonesia, the Caribbean Islands, the Philippines and the Aleutian
Islands.
The Andes Mountains in South
America were formed as a
collision…
between a continental and an oceanic
plate
Hot Spot
•
An area where
magma deep within
the mantle melts
through the crust
like a blow torch.
The Hawaiian
Islands formed as
the Pacific plate
drifted over a hot
spot.
Volcanic Eruption
Text pgs. 97-99
Magma
forms in the asthenosphere beneath the
lithosphere under great pressure. Liquid magma rises until it reaches the
surface or becomes trapped beneath layers of rock. text pages 96-97
•
A molten
mixture of
rock-forming
substances,
gases, and
water from
the mantle
is called
magma.
Volcanic Activity- A volcanic eruption is much like carbon
dioxide dissolved in soda rushing out when the soda is opened.
The gases dissolved in magma rush out carrying magma with them
Text pgs. 93-97
Magma Chamber and Vent
All volcanoes share a
pocket below the volcano
where magma is collected
and a crack to the surface.
Parts of a VOLCANO
A lava flow is the
area covered by lava
as it pours out of a
vent.
A crater forms at the
top of the volcano’s
central vent.
pipe
The pipe of a
volcano is a vertical
crack in the crust..
Magma chamber
Magma
Characteristics of Magma
depend on…
dissolved gases (bubbles out on
surface)
temperature (hotter – flows more
fluidly)
silica content (more - the thicker
it is)
text pages 96-97
Rock
Types
Light-colored and slow (too sticky)
High in silica (affects color and thickness)
Examples: Rhyolite (composition like granite) A
Low in silica
Pumice – gas bubbles are trapped and
cool quickly)
Obsidian – forms when high-silica lava
cools quickly
Dark colored and flows easily
Basalt can sometimes form these
six-sided columns seen below
•
When
magma
reaches
the
surface.
•
Text pg.97
Lava
Examples of lava types
Aa
Pyroclastic Flow
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A type of explosive
eruption that hurls out a
mix of hot gases, ash,
cinders, and effects of a
bomb.
Dormant
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A volcano that is still and
active and will awaken in
the future.
Extinct
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A dead volcano that will
no longer erupt. Volcano
is declared extinct after
50- 100 years of no
eruptions.
Geyser
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A fountain of water and
steam that erupts from
the ground. Water is
heated by hot rocks near
magma pockets. The
geyser releases pressure
from superheated water
as it erupts.
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How geysers work
VOLCANIC LANDFORMS
Text pgs. 103-107
Landforms from Volcanoes
Landforms from Lava and Ash
“How do they get their names?”
Composite
Cinder Cone
Shield
What kinds of lava are connected
with volcano type?
Shield volcano
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They are usually form from
many layers of lava. They are
named for their large size and
low profile, resembling a
warrior's shield. This is caused
by the highly fluid lava they
erupt. They result from quiet
eruptions. The Hawaiian Islands
are shield volcanoes. It is a
gently sloping mountain formed
by repeated lava flows (e)
Composite (Strato-) Volcano
A volcano built up by
many layers (strata) of
hardened lava pumice
and volcanic ash. Three
examples of this type of
volcano are Mt. Fuji, Mt.
St. Helens, and Mt. Hood.
Their eruptions can be
both quiet or explosive. It
is a mountain formed by
lava flows alternating with
explosive eruptions. (b)
Cinder Cone
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A steep hill-like volcano
that slopes steeply. It is a
cone-shaped mountain
formed from ash,
cinders, and bombs.(c)
Lava Plateau
High, level area formed by repeated
lava flows (a)
Instead of forming mountains,
some eruptions of lava form high,
level areas called lava plateaus.
First, lava flows out of several
long cracks. The thin, runny lava
travels far before cooling and
hardening. This process repeats
itself over and over again forming
a plateau. An example is the
Columbia Plateau that covers
parts of Washington, Oregon,
and Idaho.
Columbia Plateau
Caldera
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The huge hole left by the collapse of a volcanic
mountain. (d)
Soils from Lava and Ash
When volcanic
ash breaks
down, it
releases
potassium and
phosphorus,
both of which
are needed by
plants.
Volcanic Neck
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It looks like a giant tooth stuck in the ground. Forms
when magma hardens a volcano’s pipe.
Five Features formed by Magma
1. Volcanic necks
2. Dikes
3. Sills
4. Batholiths
5. Dome mountains
Dikes, Sills, Batholiths
A dike is when magma forces itself
across rock layers while magma that
squeezes between layers of rock is
called a sill.
Batholiths are a mass of rock that has
been formed when a large body of
magma cools inside the crust.
Dome Mountain- other smaller bodies of magma can
create dome mountains which form with rising magma being blocked by horizontal
layers of rock . The magma pushes the layers to bend upward into a dome shape.
Eventually the rock above the dome wears away, leaving it exposed. One
example is the Black Hills in South Dakota.
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