Transcript Earth Science Notes Volcano Types

Earth Science Notes
Volcano Types
Factors Affecting Eruptions
• Trapped Gases
– Carbon dioxide and water vapor get trapped
in magma and escape when pressure
decreases
– Gases that build up a lot of pressure cause
explosive eruptions
Factors Affecting Eruptions
• Silica
– Silica is a compound composed of silicon and oxygen
– Magma that is silica-rich is produces explosive
eruptions
• Granitic magma
• Found at subduction zones
• Lava is more runny in consistency
– Magma that is silica-poor produces quiet explosions
• Basaltic magma
• Found at hotspots
• Lava is thicker more viscous in consistency
Forms of Volcanoes
• Shield Volcanoes
– Forms from the build up of quiet eruptions
through vents or fissures
• Resembles a warriors shield
– Has gently sloping sides
– Basaltic lava flows from here
Shield Volcanoes
Shield Volcanoes
Forms of Volcanoes
• Cinder Cone Volcanoes
– Forms from the build up of explosive
eruptions
• Bits of rock called tephra are blown into the air
and fall to the ground. Over time the sides of this
volcano forms
– Resembles a giant cone
• Very steep side with loosely packed stone
Cinder Cone Volcanoes
Cinder Cone Volcanoes
Forms of Volcanoes
• Composite Volcanoes
– Intermediate between cinder cone and shield
volcanoes
– Eruptions vary some may be explosive others
quiet
– Alternating layers of tephra and lava form the
sides of the volcano
– Found near subduction zones
Composite Volcanoes
composite volcano
Composite Volcanoes
Composite Volcanoes
Forms of Volcanoes
More Volcano Types
Features Of Volcanic Activity
• Batholiths – formed when magma cools
underground
Features Of Volcanic Activity
• Volcanic Neck – magma inside volcano
cools and outside is eroded away
Features Of Volcanic Activity
• Dike – magma that cools in vertical cracks
Features Of Volcanic Activity
• Sill – magma that cools in horizontal
cracks
Features Of Volcanic Activity
• Caldera – top of volcano collapses on
emptied magma chamber
Photograph by M. Williams, National Park Service, 1977
Features Of Volcanic Activity
Volcanoes Destructiveness
Mount Vesuvius - 79 AD
Volcanoes Destructiveness
• Mount St. Helen - Washington
Volcanoes Destructiveness
Volcanoes Destructiveness
This Diagram shows range of potential destruction
A super-eruption has
the potential to cover
the United States in 3
feet of ash from a
plume. Pyroclastic flow
would engulf the
greater part of three
states, and there is
evidence that the last
major 'super' eruption
plunged the world into
a freezing, volcanic
winter that lasted a
decade. An eruption
would devastate world
agriculture, severely
effect the distribution of
food and cause mass
famine.
After the Aftermath
Summary
• Volcano Types
– Shield / cinder cone / composite / others
• Features of Volcanic Activity
– Intrusive Igneous Rocks (CH 5)
• Destructiveness of Volcanoes
• The Circle of Life