Volcanoes

1. Volcanoes

2. The cause of it all… • What causes volcanoes to erupt??? • The shift in the Earth’s plates are what causes volcanoes to form. • As the plates join or separate some of the molten rock is exposed. • Viscosity = resistance of a fluid to flow.

3. Where do volcanoes erupt??? • Convergent plate boundaries w/ subduction– the descending Oceanic plate melts and the resulting magma rises up to the crust. • Divergent plate boundaries – where two of Earth’s plates move apart. • Hot spots – active areas below the earths crust. (Hawaiian Islands)

4. Where do volcanoes erupt??? (click on it)

5. Structure of a Volcano • Magma – the molten, or liquid-like, rock within the Earth • Lava – magma that reaches Earth’s surface • Vent – an opening through which molten (liquid-like) rock flows onto Earth’s surface • Volcanoes always have one central vent, but can also have several smaller side vents.

6. ash cloud lava central vent side vent old layers of lava magma Earth’s crust Structure of a Volcano

7. Types of Volcanoes There are three major types of volcanoes: • Shield volcanoes • Stratovolcano (Composite volcanoes) • Cinder cone volcanoes

8. Shield Volcanoes • The magma inside a shield volcano is rich in iron and magnesium (Fe and Mg) and is very fluid. (low viscosity = thin) • Since the magma is very fluid, the lava coming out of the volcano tends to flow great distances. • When shield volcanoes erupt, the flowing lava gives the volcano the shape of a gently sloping mountain.

9. Shield Volcanoes • Eruptions of shield volcanoes are mild and can occur several times. • Mauna Loa in Hawaii is an example of a shield volcano.