volcanic eruptions 11/5/14 9-1/9-2 pgs. 222-229 in: what do you think causes a volcanic eruption to...
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Volcanic Eruptions 11/5/14
9-1/9-2 pgs. 222-229IN: What do you think causes a volcanic eruption to sometimes be explosive and others to just run?
Volcano
A mountain that forms when molten rock, called magma, is forced to the Earth’s surface.
What determines how it will erupt? Magma composition
High water content can cause increased pressure as the water turns to steam and expands
Silica rich magma is sticky and clogs the vents of volcanoes plugging them and preventing the release of the pressure.
basalt granite
What is difference between lava and magma?
Magma is inside the Earth.Lava is on the Earth’s Surface.
Nonexplosive Volcano
Volcanoes that have relatively calm outpourings of lava releasing a huge amount of molten rock.
Lava flows from non explosive volcanoes
Blocky lava: jumbled heaps of sharp-edged chuncks
Pahoehoe: flows slowly like candlewax with glassy surface and roundedwrinkles
Aa: Flows fast forming abrittle crust with jaggedpieces
Pillow: Forms under water in lumps that look like pillows
Explosive Volcano
Clouds of hot debris and gases shoot out from the volcano often at supersonic speeds.
Pyroclastic Material
Rock fragments created by explosive volcanic eruptions.
Four types of Pyroclastic Material
Volcanic blocks: the largest pieces of solid rock blasted out of the volcano.
Volcanic bombs: large blobs of magma that harden in the air.
Lapilli: “little stones” of pebble-like bits of magma that become solid before they hit the ground.
Volcanic ash: form when the gas bubbles of stiff magma explode into tiny glasslike slivers.
9.2 Volcanoes’ Effects on Earth Flows and Fallout: clouds of hot ash flow at supersonic speeds downhill, choking and searing
everythingin their path. Ash combines with glaciers creating acement like mixture that can dam up rivers…called alahar. It is an effective fertilizer, but when it reaches
theupper atmosphere it blocks out the sun cooling averageglobal temperatures.
3 Types of Volcanoes
Shield volcanoes Cinder cone volcanoes Composite volcanoes
Shield Volcanoes
Built out of layers of lava from repeated nonexplosive eruptions.
Cinder Cone Volcanoes
Small volcanic cones made entirely of pyroclastic material.
Composite Volcanoes
Form by explosive eruptions of pyroclastic material followed by quieter outpourings of lava. Most common.
Forms when a magma chamber that supplies material to a volcano empties and its roof collapses leaving a large circular depression.
Calderas
Out
Explain how some volcanoes erupt explosively and some do not.