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Volcanoes Nat Geo

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Volcanoes Nat Geo. Volcanic Eruptions (pages 209–216). Magma Reaches Earth’s Surface (pages 210–211). Students will be able to…. Explain what happens when a volcano erupts. Describe the two types of volcanic eruptions. Identify a volcano’s stages of activities. Students will be able to….

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slide4

Students will be able to….

Explain what happens when a volcano erupts.

Describe the two types of volcanic eruptions.

Identify a volcano’s stages of activities.

slide5

Students will be able to….

Explain what happens when a volcano erupts.

slide6

KeyConcept:Whena volcano erupts,theforceoftheexpanding gases pushes magmafrom the magmachamberthrough the pipe until it flows or explodesout of the vent.

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A volcano has a pocket of magma below the surface,called a magmachamber.A long tube, called a pipe,connects the magma chamber to the surface.

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Atthetopofapipeisanopeningcalledavent.Magma leaves the volcano through the vent and becomes lava.The area coveredbylava as it pours out of a vent iscalled alavaflow.

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As magma nears the surface, pressure on the magmafalls.Dissolved gases in magma start to formbubbles.The bubblestake up more space than the dissolvedgases.The bubblesforce magma out of the vent,likethe bubbles that force warm pop out of a bottle.

slide12

Circle the letter of the choice that explains why a volcano erupts.

a.Dissolved gases in magma form bubbles, forcing the magma out of a vent.

b.Magma gets warmer and less dense as it nears the surface, causing the magma to flow out of a pipe.

c. Pressure on magma increases as it nears the surface, forcing the magma into a magma chamber.

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Read the words in the box.Use the words to fill in theblanks in the diagram of a volcano.

Magma chamber Pipe Lavaflow Vent

Vent

A.

Pipe

B.

Lava Flow

C.

D.

Magma Chamber

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Students will be able to….

2. Describe the two types of volcanic eruptions.

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When magma pours out of a volcano, it is called avolcanic eruption.An eruption can happen slowly andquietly.Or an eruption can happen all at once with an explosion.How a volcano erupts depends on themagma.

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Avolcanoeruptsquietlyifthemagmaislowinsilicaandflows easily.The lava may flow for many kilometers before it starts to harden into rock.

a volcano erupts with an explosion if the magma is high in silica and does not fl o w easil y
Avolcanoeruptswithanexplosionifthemagmaishighinsilicaanddoesnotfloweasily.Avolcanoeruptswithanexplosionifthemagmaishighinsilicaanddoesnotfloweasily.
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Magmabuildsupinthe pipe until it explodes out of the vent.The lava coolsquickly.The hard lava pieces range in size from ashes and cinders to very large chunks called bombs.

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What explains whether a volcano has a quiet or explosive eruption?

a. how much space there is in the magma chamber

b. how much magma there is in the pipe

c. how much silica there is in the magma

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Quiet

Explosive

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Students will be able to….

3. Identify a volcano’s stages of activities.

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Key Concept: Geologists often use the terms active, dormant, or extinct to describe a volcano’s stage of activity.
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A volcano is dormant when it is no longer erupting but is likely to erupt again in the future. A dormant volcano may not erupt for thousands of years. But it can become active at any time.

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Scientists try to predict when a volcano will erupt. They watch for signs that magma is moving upward.
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Scientists often can predict when a volcano will erupt. But they cannot predict what kind of eruption or how strong an eruption it will be.
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A volcano that is no longer likely to erupt, even in the future, is

A volcano that is no longer erupting but is likely to

erupt again in the future is

extinct

dormant

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How do scientists try to predict volcanoes? a. by measuring the amount of silica in magma

b. by measuring the size of the magma chamber

c. by watching for signs that magma is moving upward

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