Volcanoes. volcano – weak spot in the crust where magma comes to the surface magma – a molten...
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Transcript of Volcanoes. volcano – weak spot in the crust where magma comes to the surface magma – a molten...
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