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Chapter 3 Lesson 3
Volcanoes
Where are volcanoes found?
• Volcanoes form on land and on the ocean floor.
• Volcanoes are only located in certain places on the Earth’s surface.
• Volcanoes are found where two plates meet.
Where are volcanoes found?
Where are volcanoes found?
• A circle of volcanoes called the Ring of Fire, surrounds the Pacific Ocean.
• Volcanoes are more likely to erupt at plate boundaries than anywhere else on Earth.
• An eruption is an outpouring of melted rock, ash, gases, or a combination of these.
Volcanoes
Where are volcanoes found?
• However, volcanoes do not erupt at all plate boundaries.
• What makes some plate boundaries likely places for volcanoes to erupt?
• Scientists conclude that volcanoes tend to erupt where one plate is pushed under another plate.
Where are volcanoes found?
• When rocks in the plate that is being pushed down reach the heat and pressure in the mantle, they melt
• Magma forms and pools in a chamber underneath the crust.
• The magma may rest quietly for hundreds or thousands of years.
Where are volcanoes found?
• Sometimes, a crack forms above the chamber or the pressure in the chamber grows too great to be held in by the rock above it.
• Then the magma rushes upward toward Earth’s surface.
• All volcanoes have at least one vent, or opening. Once magma reaches Earth’s surface, it is called lava.
Volcanoes
Volcanoes
• Over time, a cup-shaped depression may form around a vent.
• This depression is called a crater. • Sometimes the magma chamber beneath a
volcano is emptied. The volcano may then collapse inside itself.
• The hole that forms is called a caldera.
How do volcanoes affect land areas?
• Gentle Eruptions: Some volcanoes allow these gases to escape without a great deal of pressure building up.
• These gentle eruptions produce large amounts of lava, but few explosions.
• Eruptions in Hawaii are usually of this type.
How do volcanoes affect land areas?
Explosive Eruptions
• Other volcanoes do not let gases easily escape.
• The pressure in the magma chamber builds until an explosion occurs.
• These volcanoes throw ash, rock, and lava high into the air.
• The rock and ash can land far from the erupting volcano.
Explosive Eruptions
Explosive Eruptions
Warning Systems
• Scientists can often predict when a volcano is about to erupt.
• Small earthquakes cause by magma rising to the surface usually occur.
• A tiltmeter is a tool that measures small changes in the tilt of the earth’s surface. They are used to monitor volcanoes.
Warning Systems
• As magma pushes upward, in a volcano, the Earth’s surface will lift and tilt.
• A tiltmeter can detect changes and alert scientists of the data.
How do volcanoes build land?
How do volcanoes build land?
• Dike: Hardened magma, in vertical cracks.• Sill: Hardened magma formed in horizontal
layers of rock.• Laccolith: Magma pushed upward and forms a
dome shape.• Batholith: largest and deepest of all
underground magma, huge and irregularly shaped.
How do volcanoes build land?
• Vent: Opening where magma comes out of the Earth.
• Active volcano: erupting or has recently erupted.
• Dormant volcano: volcano that does no erupt for some time.
• Extinct volcano: volcano that has stopped erupting. Considered dead.
How do volcanoes build land?
How do volcanoes build land?
• Shield volcano: built by thinner, fluid lava that spreads over a large area. Broad base and gently sloping sides.
How do volcanoes build land?
How do volcanoes build land?
• Cinder-cone volcano: built by thick lava that is thrown high into the air and falls as chunks or cinders. These mountains form as a cone shape with a narrow base and steep sides.
How do volcanoes build islands?
• Island chain: Hawaiian Islands are a line of volcanic mountains.
• Islands form as plates pass over a stationary pool of magma called a hot spot.
How do volcanoes build islands?
How do volcanoes build islands?
