Download What are Volcanoes?

December 02, 2014
Agenda
1. Roll
2. PowerPoint: Volcanic
Eruptions Part 1
3. Possible Video
Have your science notebook
out and open to the next
blank page.
Subject Area: Volcanic Eruptions
EQ: What are volcanoes?
Questions:
1. What is the difference between an
explosive and a nonexplosive eruption?
2. How does the composition of the magma
determine the type of eruption?
3. What are the main types of lava and
volcanic debris?
Volcanic Eruptions
Think about the force of the explosion of an
atomic bomb. Now imagine an explosion
10,000 times stronger. This is the possible
power that can come from a volcanic
explosion.
Nonexplosive Eruptions
Often people think of a river of red-hot lava
when they think of a volcanic eruption.
Lava flow is a river of hot lava. Lava flows
are common in nonexplosive eruptions
where the lava flows continually.
Sometimes they will spray, they are not
explosive.
Explosive Eruptions
In an explosive eruption, clouds of hot debris
and gases shoot out from the volcano,
often at supersonic speeds. Instead of
lava these volcanoes blow molten rock
into the air where it will harden. The larger
pieces fall to the Earth and the smaller
portions can circle the globe for years in
the upper atmosphere.
Explosive Eruptions
An explosive volcano can also blast millions
of tons of solid rock. This rock could have
accumulated over millions of years. This
means that a volcano can actually shrink
after an eruption.
Movie
Cross Section of a Volcano
All volcanoes share the same basic
features. They all have magma. Magma is
the hot liquid material that is the driving
force of creating volcanoes.
Cross Section of a Volcano
Magma rises through holes in the Earth’s
crust called Vents.
Cross Section of a Volcano
Magma that erupts and flows onto the
Earth’s surface is called Lava.
Cross Section of a Volcano
Magma that erupts as fragments of molten
material that solidify in the air is called
pyroclastic material.
Cross Section of a Volcano
A vent or a group of vents combined with the
buildup of lava or pyroclastic material on
the Earth’s surface is a volcano.
Magma
By comparing the composition
of magma from different
types of eruptions, scientists
have discovered that the
composition of magma
determines whether a
volcanic eruption is
nonexplosive, explosive, or
somewhere in between.
Magma
Water: A volcano is more likely to erupt
explosively if its magma has a high water
content. The effect of water on magma is
similar to the effect of carbon dioxide gas
on a can of soda when you shake it up.
Magma
Silica: Explosive eruptions are also caused
by magma that contains a large
percentage of silica. This type of magma
tends to move slowly and harden in the
Partner Share:
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The Story of a Volcano
Questions for your
Science Notebook
The Story of a Volcano
What did you know?
Skip 5 lines
What did you learn?
Skip 5 lines
What do you want to know?
Skip 5 lines
Why does the family choose to continue to live near a volcano?
What Erupts From a Volcano?
Nonexplosive eruptions produce mostly
lava. Volcanoes can change and produce
pyroclastic material. Explosive eruptions
will produce both pyroclastic material and
lava.
Partner Share:
Is a nonexplosive volcanic eruption more likely to produce lava
or pyroclastic materials?
A nonexplosive volcano produces …
What Erupts From a Volcano?
Lava: Lava is magma that
flows to the Earth’s
surface. It can be thick and
thin. Blocky lava is thick
and barely moves along.
Other lava such as
pahoehoe, aa, and pillow
lava, are thinner and
produce faster lava flows.
movie
Blocky lava
Blocky lava is cool, stiff lava that cannot
travel far from an erupting vent. Blocky
lava forms in jumbled heaps of sharp-edge
chunks.
Pahoehoe
Pahoehoe lava flows slowly, like wax
dripping from a candle, forming a glassy
surface with rounded wrinkles. Pahoehoe
gets its name from the Hawaiian word for
“ropy” because its surface resembles the
coils of a rope.
Aa
Aa is a Hawaiian word that refers to a type
of lava that has a jagged surface. Aa is
named after the sound you would make if
you were to walk across this type of lava
barefoot.
Partner Share:
What is aa?
Aa is …
Pillow Lava
Pillow lava forms when lava erupts
underwater. Pillow lava has a rounded
shape because contact with water causes
rapid cooling of the lava’s surface.
What Erupts From a Volcano?
Pyroclastic Material: Pyroclastic material is
the rock fragments created by explosive
volcanic eruptions. It comes in a variety of
sizes, from boulders the size of a house to
particles so small they can remain in the
atmosphere for years. There are four
major types of pyroclastic material:
volcanic bombs, volcanic blocks, lapilli,
and volcanic ash.
Volcanic Blocks
Volcanic blocks are the largest pieces of
pyroclastic material, they consist of solid
rock blasted out of a volcano.
Partner Share:
What is a volcanic block?
A volcanic block is …
Volcanic Bombs
Volcanic bombs are large blobs of magma
that harden in the air.
Lapilli
Lapilli are pebble-like bits of pyroclastic
material. They cool in the air and are solid
when they hit the ground.
Volcanic Ash
Volcanic ash is small particles that are less
than 2 mm in diameter. Volcanic ash forms
when gases in stiff magma expand rapidly
and the walls of the gas bubbles explode
into tiny glasslike slivers.
Partner Share:
How is volcanic ash made?
Volcanic Ash is made by …
Summary
1. Answer the essential question “What are
Volcanoes?”
2. Your answer needs to be in complete sentences.
3. Place your answer at the bottom of the notes we
did yesterday and today.
4. Make sure you use the definition of a volcano
from your notes.
5. You may also write about the difference between
explosive and nonexplosive volcanoes.
6. You can write about pyroclastic material and the
different types of lava.
Into the Volcano
Questions for your
Science Notebook
Into the Volcano
What did you know?
Skip 3 lines
What did you learn?
Skip 3 lines
What do you want to know?
Skip 3 lines
Objectives:
1. Distinguish between nonexplosive and
explosive volcanic eruptions.
2. Explain how the composition of magma
determines the type of volcanic eruption
that will occur.
3. Classify the main type of lava and
volcanic debris.