Volcanic Eruptions
What happens before??
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Dissolved gases in magma are trapped and are under extreme pressure (keeps it from erupting)
Magma rises
Pressure of surrounding rock decreases
Gasses can expand and form bubbles
Pressure continues to fall and bubble get bigger and bigger (exert a LOT of force)
Force from expanding gasses pushes magma from the chamber through the pipe until it flows or explodes out of
the crater or vent
Kinds of Eruptions:
Depends on 1) Silica Content 2) Viscosity
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Quiet Eruptions
o Description:
 Magma is low in silica
 Low viscosity and flows easily
 Gases bubble out gently
 Lava oozes from vents
 Some spurting
 Produce pahoehoe and aa
o Damage: sets fires, buries anything in its path, covers large areas
Explosive Eruption
o Description:
 Magma has high silica content
 High viscosity making it thick /sticky
 Builds up (like a cork) holding in gases
 Explode when pressure is too much
 Lava shot into air breaks into fragments and cools in air
 Smaller pebble sized are cinders
 Larger pieces called bombs
 Forms pumice and obsidian
 Pyroclastic flow is formed from gases, ash, cinders and bombs
o Damage: Destroys anything in its path, pyroclastic cloud kills organisms , causes landslides and
avalanches and stalls airplane engines
Volcanoes of the Past
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Mt. Vesuvius 79 A.D. – completely destroyed and preserved the city of Pompeii
Krakatau 1883- shot a pyroclastic cloud a record 18km in to the air
Mt. Pelee 1902- only 2 people survived this Caribbean eruption
Mt. Saint Helens 1982- eruption caused a massive landslide
E-Kull (Eyjafjallajökull) 2010- erupted with a pyroclastic cloud that was so large it shut down airports
Olympus Mons-largest volcano in the solar system. Located on Mars. The size of Arizona
Monitoring Volcanoes
Geologists have been more successful in predicting volcanoes than in predicting earthquakes.
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Measure:
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changes in elevation caused by magma moving underground- Tiltmeter
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Escape of gases
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Temperature increase of ground water
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Small earthquakes around a volcano
Does NOT predict type or power of eruption