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Volcanic Eruptions
7.3
p.209-216
Inside a volcano
Magma chamber- holds the magma Pipe- tube that connects the magma chamber
to the surface Vent-place where magma reaches the
surface Lava flow- area covered after the volcano
erupts Crater- the bowl shape area that forms
around the central vent
The Eruption
Volcanoes erupt when the pressure gets too great and the gases and magma rises in the pipe. As it goes up toward the surface the pressure decreases and the gas bubbles expand so much that they form bubbles and increase in size. This increase in size exerts a force on the top of the volcano and it erupts.
- Volcanic Eruptions
Kinds of Volcanic Eruptions
Volcanoes are either quiet or explosive. Depends on the silica content and viscosity. Quiet eruptions: low in silica, low viscosity,
flows and oozes over many kilometers produces Aa and pahoehoe
Ex: Hawaii
Hawaii
Explosive
Explosive eruptions: high in silica, high viscosity- this sticky substance does not flow in the pipe easily and it tends to get clogged causes lots of pressure to build up. Erupts and causes dust, ash, cinders, and bombs to fall. Also causes pyroclastic flows
EX: Mt. St. Helens
Mt. St. Helens
Mount St. Helens
Volcanic Hazards
Quiet eruptions cause flowing lava to flow from the vent and set fire to and burn everything in its path and cover large area with thick layers of lava.
Explosive Eruptions cause towns to be buried in volcanic ash causing roofs to collapse, plane crashes, landslides and avalanches of mud
Life Cycle of a volcano
Active- volcano that is erupting or has shown signs that it may erupt in the near future.
Dormant- sleeping volcano could awaken in the future and erupt again.
Extinct- dead volcano unlikely to erupt again. Some volcanoes only erupt every several
hundreds or thousands of years and are dormant for long periods of time.
Monitoring Volcanoes
Predicting volcanoes is an easier job than predicting earthquakes. Volcanoes give off signs to scientists such as elevation changes that can be detected with a tiltmeter, gases can be monitored, temperature changes can be detected, and earthquakes that occur close to site are watched by a seismograph.
7.4 Volcanic Landforms
Pages 217 to 223
Landforms from Lava and Ash Shield Volcanoes
Produced by slowly venting volcanoes that pour layer over layer of lava on top of eachother.
Cinder Cone Volcanoes Produced by ash, cinders, and lava bombs into a high
volcano Composite Volcanoes
Combination of slow lava flows and explosive ash, cinder, and lava
Lava Plateaus Formed by thin, runny lava that oozes out of cracks
Shield Volcano
Cinder Volcano
Composite Volcano
Lava Plateau
More Lava Forms
Calderas Huge craters formed by supervolcanoes that
collapse into the magma chamber. Uses for volcanic soil
Volcanic soil is initially barren, but after the soil breaks down it releases potassium, phosphorus, and carbon
Once broken down volcanic soil is very fertile
Yellowstone Caldera
Yellowstone Caldera
Yellowstone Caldera
Landforms From Magma
Volcanic Necks Magma from a volcano’s pipe hardens and leaves
a giant “tooth” in the earth Dikes and Sills
Dike – Formed by magma slanting through bedrock sideways
Sill – Formed when magma squeezes between horizontal layers of rock
Volcanic Neck (Monument Valley)
Dike (Stairway to Heaven, Spain)
Sill (Palisades, NJ)
Landforms from Magma Cont’d Batholiths
Huge masses of rock formed when magma cools inside he crust
Dome Mountains Hardened magma pushes rock above it up,
creating small mountains and hills
Sierra Nevada Batholith
Dome Mts (Black Hills, SD)
Geothermal Activity
Comes from the Greek, “geo” means “Earth” and “therme” means “heat.”
Hot Springs Large super-heated pools of water
Geysers Release super-heated water at intervals when
pressure builds high enough
Hot Springs, Iceland
Geysers, Old Faithful, Yellowstone