Volcanoes

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*

Volcanoes & Plate Tectonics

-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.

Volcano Formation

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 collideExamples: 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

Volcanoes & Plate Tectonics

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 darkcolored 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

Properties of Magma