Complete the paragraph below
 Lava begins as
, which usually forms in
the asthenosphere. The materials of the
asthenosphere are under great pressure. Liquid
magma is
dense than the solid material
around it. Therefore, magma flows upward into
any cracks in the rock above. As magma rises, it
sometimes becomes trapped beneath layers of
rock. But if an opening in weak rock allows the
magma to reach the surface an
occurs.
Volcanic Eruptions
What happens??
 https://www.youtube.com/watch?v=ijVL6hBJibA
 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 gasess pushes magma from the
chamber through the pipe until it flows or explodes out of the
crater or vent
Kinds of Eruptions
Quiet
Explosive
Depends on:
-Silica Content
-Viscosity
Quiet Eruptions
• Magma is low in silica
• Low viscosity and flows easily
• Gases bubble out gently
• Lava oozes from vents
• Some spurting
• Produce pahoehoe and aa
Damage from Quiet Eruptions
 Sets fires
 Buries anything in its path
 Covers large areas
Explosive Eruptions
 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
 Pyroclastic flow is formed from gases, ash, cinders
and bombs
 Forms pumice and obsidian
Damage from Explosive Eruptions
 Destroys anything in its path
 Pyroclastic cloud kills organisms
 Causes landslides and avalanches
 Stalls airplane engines
The Power of Volcanoes
1883
Krakatau
1902
Mount Pelee
The Power of Volcanoes
1982
Mt. St. Helens
2010
Eyjafjallajökull
The largest volcano in the solar system…
https://www.youtube.com/watch?v=ySFpJclnzU
Monitoring Volcanoes
Geologists have been more successful in predicting volcanoes
than in predicting earthquakes.
 Measure changes in elevation caused by magma moving
underground- Tiltmeter
 Can monitor escape of gases
 Temperature increase of ground water
 Small earthquakes around a volcano
 Does not predict type or power of eruption