1. Volcanoes

2. Volcanoes & Plate Tectonics
volcano – weak spot in the crust where magma comes to the surface
magma – a molten mixture of rock, minerals, gases and water beneath the Earth’s surface
lava – magma that reaches the Earth’s surface
*animation*

3. Volcano Formation -Volcanoes often form where two plates collides.
-In all situations, an oceanic plate sinks under another plate and moves through a trench.
-Due to great pressure and friction during subduction, rock above the oceanic plate melts to form magma
-Eventually, the magma erupts to the surface as lava.

6. Volcanoes & Plate Tectonics
volcanic belts
– form along boundaries of the Earth’s tectonic plates
-most occur at convergent plate boundaries
-Ring of Fire
– Earth’s largest volcanic belt that surrounds the Pacific Ocean

7. Volcanoes & Plate Tectonics
island arcs
– a string of islands formed by the volcanoes along a deep-ocean trench
-form when two oceanic plates collide
Examples: Japan, New Zealand, the Philippines

9. Volcanoes & Plate Tectonics
hot spots
-extreme heat from the Earth’s mantle rises and melts the rock above, forming pockets of magma below the Earth’s crust
-a volcano forms when the magma breaks through a weak area in the crust and reaches the Earth’s surface
*animation*
Example: Hawaiian Islands

11. Properties of Magma viscosity - the resistance of a liquid to flow
-the viscosity of magma depends on the amount of silica and temperature
silica
- a compound made of silicon and oxygen
- magma with a high silica content is light colored and has a high viscosity
- magma with a low silica content is dark colored and has a low viscosity

12. Properties of Magma pahoehoe
-fast moving, hot lava with a low viscosity aa
-slow moving, cooler lava with a high viscosity