Volcanoes

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*

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.

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

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

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

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

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