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.

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?