Download Lesson 3 Volcanoes NOTES

Chapter 5 Lesson 3 Volcanoes
Vocabulary
1. Volcano
2. Lava
3. Shield volcano
4. Cinder-cone volcano
5. Composite volcano
6. Island chain
7. Hot spot
8. Island arc
NOTES
Where are volcanoes found?
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Volcanoes form on land and on the ocean floor.
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Found on certain places on Earth’s surface.
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Most are found where plates meet.
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Ring of Fire-circle of volcanoes surrounding the Pacific Ocean.
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More likely to erupt at plate boundaries than anywhere else on Earth.
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An eruption is an outpouring of melted rock, ash, gases, or a combination of these.
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Scientists concluded that volcanoes tend to erupt where one plate is pushed under another
plate.
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When rocks in the plate that is being pushed down reach the heat and pressure in the mantle,
they melt.
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Magma forms and pools in a chamber underneath the crust.
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Magma may rest quietly for 100s or 1000s of years.
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A crack forms above the chamber or the pressure in the chamber grows too great to be held in
by the rock above it.
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The magma rushes toward the surface.
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More than 80% of Earth’s volcanic activity occurs on the ocean floor.
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All volcanoes have at least one vent, or opening.
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Lava, ashes, and gases erupt through vents.
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A cup-shaped depression called a crater may form around the vent.
o
This is usually found at the top of a volcanic mountain.
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Sometimes the magma chamber beneath a volcano is emptied.
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The volcano may then collapse inside itself. The hole that forms is called a caldera.
How do volcanoes build land?
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Sometimes magma cools and hardens before it reaches the surface.
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A dike forms when magma hardens in vertical or nearly vertical cracks.
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A sill forms when magma hardens between horizontal layers of rock.
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Sometimes the magma pushed into a sill does not spread horizontally, but pushes upward.

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It forms a dome shape called a laccolith.
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Laccolith may raise the rock layers above it when formed.
The largest and deepest of all underground magma formations are batholiths.
o
Batholiths are huge and irregularly shaped.
o
Reaches deep into the crust.

When lava comes out of a vent, it is liquid.
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Lava forms a solid layer of rock as it hardens.
o

Layers increase the height of a volcano and form a volcanic mountain.
Active Volcano-currently erupting or has erupted.
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Dormant Volcano-doesn’t erupt for a long time.
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Extinct Volcano-volcano that stops erupting or is dead.
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Active volcanoes differ in how they form and in the shapes of the mountains they build.
o
Shield volcano, cinder-cone volcano, and composite volcano. (SEE VOCABULARY)
How do volcanoes build islands?
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The Hawaiian Islands are an island chain.
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They rest on a slowly moving tectonic plate.
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As it moves, the plate passes over a stationary pool of magma call a hot spot.
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Lava erupting from the hot spot formed a mountain that eventually becomes a volcanic island.
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As the plate moved, that island moved away from the hot spot and a new island began to form.

In areas where an ocean-floor plate is pushed under another ocean-floor plate an island arc is
formed.
o
As the plate is pushed down it melts.
o
Magma forms, rises upward, and erupts through the ocean floor.
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The eruptions form a series of volcanic islands along the plate boundary.
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The Aleutian Islands in Alaska form an island arc.