What are volcanoes?

• How many active volcanoes in the world?– Over 600

• What is the world’s most active volcano?

• Vocab words:– Vent– Magma chamber– Crater– lava

Why does magma move towards the surface?

• Magma is less dense than surrounding rock.

Where does magma form?

Volcanic Vent

• The opening of a volcano where the magma escapes to reach the earth’s surface

Craters

• The steep walled depression around a volcanoes vent

How do Volcanoes Form?

heat and pressure changes the rock to melt forming liquid magma

Magmas less dense than rock, forced slowly towards earth’s surface

Effects of Eruptions

• Floods• Lava Flows• Ash, rock, chemicals in the air (acid rain)• Burning• New land masses• Destruction• Mud Flows

Kilauea in Hawaii

The Hawaiian name "Kilauea" means "spewing" or "much spreading," in reference to the lava flows

• Most Recent EruptionContinuous since January 3, 1983

• Number of Historical Eruptions 61

Effects of Eruptions

• Ash – harmful to life, buildings, roads

• High temperatures – can ignite wood

Mt Spur, Alaska

Montserrat

Montserrat 1995 - 2004

• Pyroclastic flow – hot volcanic gas and ash moving in a cloud directly over the Earth’s surface

• Acid rain – results when sulfur gases from volcano mix w/ water in the atmosphere– Harmful to vegetation and aquatic life

Where do volcanoes occur?

• They often occur when Earth’s tectonic plates:– Move apart – divergent boundary– Move towards each other – convergent

boundary– At “Hot Spots” – where crust of Earth is

thinner than normal

Divergent boundary

Iceland

Mid-Atlantic Ridge

Hekla

• Hekla is located in Iceland

• last erupted on February 20, 2000

• At a divergent plate boundary

• composite volcano• began erupting in

1819

Iceland

Iceland

Convergent boundary

Mt St Helens

Soufriere Hills on Montserrat

• Example of a convergent boundary responsible for volcanism