volcanoes
TRANSCRIPT
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Chapter 7 VOLCANOES
Sect. 1 & 2
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Volcanism• Mov’t of magma toward or onto the
Earth’s surface magma rises cuz its less dense pushing its way to the surface
• Magma on earth’s surface = Lava• Vent = opening in earth’s surface where
magma flows through• Volcano = structure formed from vent &
material builds around it
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Major Volcanic zones
• On divergent & convergent boundaries
1. Subduction Zones
2. Mid-Ocean Ridges
3. Hot Spots
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Subduction Zones• A subducted plate is subjected to heat & friction & is forced
downward causing it to remelt & become magma• This magma will be forced to surface and forming volcanic
mountains along continental plate
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Subduction Zones• Ring of Fire is a result of plates being subducted
• There can also be collision of 2 oceanic plates forming Island Arcs or volcanic islands (ex. Japan)
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Mid-Ocean Ridges• Divergent boundary• Magma rises up through rift• Emerging lava forms new ocean floor
• Iceland is exposed part of ridge & is covered with fissures (cracks)
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Hot Spots• Magma comes to the surface from within a plate• Hot spot stays put but plate is in constant
motion forming volcanic islands
Hawaiian Islands
Galapagos Islands
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Volcanic Eruptions
Windows to Earth’s Interior
Ability to see firsthand materials from mantle
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3 General Types of Lava
1. Mafic (basaltic) low silica content and low in water vapor & CO2 dark color
2. Felsic (granitic) high silica & high in water vapor & CO2
light in color
3. Faults between mafic & felsicrange in composition
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Kinds of Eruptions• Type of lava (mafic/felsic) determine
how explosive eruption will bedemo
• Oceanic Volcanoes: produce mafic lava very thin
flow easilylow gas erupt quietly
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Kinds of Eruptions• Felsic lava (continental
volcanoes) thick lavalarge amt gases
w/lava boil out of vent explosively solid particles fly out w/ magma
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Volcanic Rock Fragments• Pyroclastics: large fragments blown
from the cone of felsic volcanoes.
< 2 mm = volcanic ash
< .25 mm = volcanic dust
< 64 mm = lapilli (lil’ stones)
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Three types of Volcanoes• Shield Volcano
covers wide areaquiet eruptionsslow build up around vent
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Three types of Volcanoes• Cinder cone
made up of solid fragmentsSteep slopesrarely highvery explosive
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Three types of Volcanoes• Composite Cone
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Three types of Volcanoes• Composite Cone
formed by alternating explosive & quiet eruptionsdevelop high volcanic mountains
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Crater vs. Caldera
• Crater = funnel shaped pit at top of vent; formed when material is blown from vent during explosions
• Caldera = large basin shaped depressions formed either by explosions or cones collapsing
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Predicting Volcanoes
• seismographs• study past history of volcanoes• bulging of volcanic slopes• changes in gases given off
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Extraterrestrial Volcanism
Many planets & moons in the solar system were and are volcanically
active
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Extraterrestrial Volcanism
The MoonCovered by Basaltic flows; no longer active; however, no evidence of plate tectonic activity
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Extraterrestrial Volcanism
MarsNumrous volcanoes & features; biggest one is shield volcano called Olympus Mons
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Extraterrestrial Volcanism
IOMoon on Jupiter; shows 9 active volcanoes erupting on Io