Download Types of Volcanoes

Types of Volcanoes
What Controls Eruptions?
• Some volcanic eruptions are _________________________, like
those from Soufriere Hills volcano, Mount
_________________________, and Mount St. Helens.
• In others, the lava ___________________ flows from a vent, as in
the ________________________ eruptions.
• Two important factors control whether an eruption will be
________________________ or _________________________.
• One factor is the amount of water ___________________ and
other gases that are trapped in the ___________________.
• The second factor is how much ______________________ is
present in the ____________________.
• Silica is a compound composed of the elements
_____________________ and _________________________.
Trapped Gas
• Gases, such as water _______________________ and carbon
dioxide are trapped in magma by the ________________________
of the surrounding magma and rock.
• As _______________________ nears the surface, it is under less
_______________________.
• This allows the gas to _____________________ from the
_______________.
• Gas escaped easily from some __________________ during quiet
____________________.
• However, ____________ that is under a lot of pressure eventually
causes _____________________ eruptions.
Water Vapor
• The ___________________ at some convergent plate
______________________ contains a lot of water vapor.
• This is because ________________ plate material and some of its
water slide under other plate ______________________.
• The ______________________ water vapor in the magma can cause
_______________________ eruptions.
1
Composition of Magma
• The second major factor that affects the
______________________ of the eruption is the
______________________ of the magma.
• Magma can be divided into two major types: silica
____________________ and silica _______________________.
Quiet Eruptions
• ____________________ that is low in silica is called
____________________________ magma.
• It is fluid and produces quiet, __________________________
eruptions such as those in _________________________.
• This type of lava pours from volcanic ____________________ and
runs down the ______________________ of the volcano.
• As this lava ____________________, it forms a
_____________________ structure.
• If the same lava flows at a lower ______________________, a
stiff, slowly moving _____________________ forms.
• In fact, you can ________________________ right up to this type
of ________________.
Explosive Magma
• _____________________ rich, or ____________________,
magma produces explosive eruptions such as those at Soufriere Hills
volcano.
• This ___________________ forms where Earth’s plates are moving
together and one plate _____________________ under another.
• As the plate that is sliding under the other plate, goes
____________________, some rock is ____________________.
• The magma is forced upward by _____________________
surrounding rock, coming into contact with the
_________________________, and becomes rich in silica.
• Silica rich, _______________________ magma is thick, and gas
gets trapped inside, causing ________________________ to build
up.
• When an _____________________ eruption occurs, the gases
expand rapidly, often carrying pieces of _________ in the explosion.
2
Andesitic Magma
• Some _____________________ have an
________________________ composition.
• ___________________ magma is more silica rich than basaltic
magma but is less silica rich than _____________________ magma.
• It often forms at ____________________ plate
___________________________ where one plate slides under the
other.
• Because of their higher ____________________ content, they also
erupt more violently than _____________________ magmas.
• One of the biggest ___________________ ever recorded,
______________________________, was made with andesitic
magma.
• Many of the ________________________ encircling the
____________________ Ocean also are made of andesitic.
Forms of Volcanoes
• A volcanoes ___________________ depends on whether it is the
result of a quiet or an ____________________ eruption and the
type of lava it is made of-basaltic, __________________, and or
andesitic.
• The three basic types of volcanoes are ____________________
volcanoes, _____________________ cone volcanoes, and
_________________________ volcanoes.
Shield Volcano
• Quiet eruptions of _____________________ lava spread out in flat
____________________.
• The buildup of these layers forms a broad ___________________
with gently sloping sides called a _____________________ volcano.
• The ____________________ islands are examples of
_________________ volcanoes.
• ___________________ lava also can flow onto Earth’s surface,
through large cracks called _______________________.
• This type of _________________ forms flood
______________________, not volcanoes.
3
•
•
•
The ______________________ lava flows over Earth’s surface,
covering large areas with thick deposits of basaltic
______________________ rock when it cools.
The _____________________ Plateau located in the
________________________ United States was formed in this
way.
Much of the new ____________________ that originates at the
mid-ocean ridge forms as underwater flood __________________.
Cinder Cone Volcano
• Explosive ______________________ throw lava and rock
_________________ into the air.
• Bits of rock or ______________________ lava dropped from the
air, called __________________.
• _______________________ varies in size from volcanic ash, to
______________________, to larger rocks called bombs and
blocks.
• When _____________________ falls to the ground, it forms a
steep-sided, loosely packed cinder ____________________ volcano.
Paricutin
• On February 20, ____________, a Mexican farmer learned about
___________________________ when he went to his cornfield.
• He noticed that a hole in his ______________________ that had
been there for as long as he could remember, was giving off
______________________.
• Throughout the _______________, hot glowing
______________________ were thrown high into the air.
• In just a few days, a ____________________ cone several hundred
meters high covered his _____________________.
• This is the __________________ named ____________________.
Composite Volcano
• Some volcanic _____________________ can vary between quiet and
violent depending on the amount of trapped gases and how rich in
_______________ the magma is.
• An ______________________ period can release gas and ash,
forming a _____________________ layer.
4
•
•
•
•
Then the __________________ can switch to a quieter period,
erupting lava over the top of the _________________ layer.
When this cycle of lava and __________________ is repeated over
and over in ________________________ layers, a composite
volcano is formed.
_____________________ volcanoes are found mostly where Earth’s
plates come together and one ________________ slides below the
other.
____________________ Hills volcano is a
_________________________ volcano.
Violent Eruptions
• ______________________ Hills volcano formed as ocean floor of
the ___________________ American Plate and the South American
Plate slid beneath the ______________________ Plate, causing
magma to form.
• Repeated ________________ of lava and tephra produces the
majestic composite volcanoes that tower above the surrounding
landscape on ___________________ and other islands in the Lesser
Antilles.
• Before the 1995 _________________________, silica-rich magma
rose and was trapped beneath the _______________________.
• As the magma was forced toward _____________________
surface, the pressure of the underlying magma was
______________________.
• This started a ____________________ of eruptions that were still
continuing in _________________.
Krakatau
• One of the most ____________________ eruptions in recent times
occurred on an island in the Sunda Straits near
______________________ in August of 1883.
• ___________________, a volcano on the island, erupted with such a
force that island _______________________.
• Most of the ____________________ collapsed into the emptied
________________ chamber.
5
•
•
•
•
The noise of the _________________ was so loud that it woke
people in Australia and was heard as far away as
_________________ km from the island.
Ash from the eruption fell in ____________________, which is
840km to the North, and the area around the
______________________ was in complete darkness for 24h.
More than _____________ people were killed, most by the giant
_____________________ waves created by the eruption.
Global ______________________ were lowered as much as 1.2
degrees C by particles blown into the _____________________ and
didn’t return to normal until 1888.
6