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