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Volcanoes

Volcanoes. October 29, 2013. What causes volcanoes to form?. Form at areas of the earth surface through which magma and volcanic gases pass Because the temperature of the mantle is fairly constant, decreasing pressure allows for magma to be formed, usually at diverging plate boundaries.

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Volcanoes

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  1. Volcanoes October 29, 2013

  2. What causes volcanoes to form? • Form at areas of the earth surface through which magma and volcanic gases pass • Because the temperature of the mantle is fairly constant, decreasing pressure allows for magma to be formed, usually at diverging plate boundaries. • Once formed it is less dense than the surrounding rock, so it rises to the surface forming a volcano

  3. What exactly is a volcano? • Actually consists of many parts: • Magma chamber – molten rock deep underground that feeds a volcano • Vent – tube that allows the molten magma to reach the surface • Volcanic body – remains of lava that have been deposited by previous eruptions

  4. Are all volcanoes the same? • No, 2 main types: • 1. nonexplosive – most common, have relatively calm flows of lava. Can release huge amounts of lava, but lava does not contain explosive gases • 2. explosive – rarer, contain highly explosive gases within lava. Produces clouds of hot debris, ash that can demolish an entire mountainside in seconds

  5. What exactly erupts from a volcano? • 2 different materials: • 1. Lava – liquid magma that flows from a volcanic vent • 4 types: • Aa – lava that pours out quickly and forms a brittle crust as it cools rapidly • Pahoehoe – lava that flows slowly, with glassy surface

  6. 3. Pillow lava – forms when lava erupts underwater, forms rounded lumps similar to pillows • 4. Blocky – forms as lava oozes from a volcano and forms jumbled heaps of sharp-edged chunks

  7. What’s the other type of material? • Pyroclastic material: • 4 types: • 1. volcanic bombs – large blobs of magma that harden in the air • 2. volcanic blocks – solid rock that are erupted from a volcano

  8. 3. lapilli – pebblelike bits of magma that harden before they hit the ground • 4. volcanic ash – forms when the gases in stiff magma expand rapidly and explode into tiny glasslike slivers, most common type of pyroclastic material

  9. How many kinds of volcanoes are there? • 3 kinds: • 1. shield cone – built by layers of lava produced by nonexplosive eruptions • 2. cinder cone – made of pyroclastic material produced by moderately explosive eruptions • 3. Composite cone – sometimes called stratovolcanoes made by explosive eruptions followed by less explosive flows

  10. Where do volcanoes form? • 3 different locations: • 1. mid ocean ridges -- form at divergent boundaries • 2. convergent boundaries -- when a thin oceanic plate slides underneath a thick continental plate • 3. hot spot – magma comes to the surface away from a tectonic plate boundary

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