Transcript Earth Science

Earth Science
Chapter 6
Volcanoes
Volcanoes and Plate Tectonics
Volcano
- a weak spot in the
crust where molten material, or
magma, comes to the surface.

https://www.youtube.com/watch?v=fmCJSS2YAP0
Magma
– molten mixture of rock
forming substances, water and
gases beneath the mantle
Lava
- Magma that reaches the
surface
Volcano
Formation
1.Along Tectonic Plate
Boundaries
2.Above a hot spot when magma
erupts through the crust and
reaches the surface.
Ring of Fire - Major Volcanic Belt
surrounding the Pacific Ocean Tectonic
Plate Boundaries
Volcanoes
along spreading
boundaries or colliding boundaries
Island
arcs – where 2 oceanic
plates collide http://www.absorblearning.com/m
edia/item.action?quick=12u
Hot Spot Volcanoes –
https://www.youtube.com/watch?v=AhSaE0omw
9o
http://education.sdsc.edu/optiputer/flash/hotSpot
s.htm
https://www.classzone.com/books/earth_science/
terc/content/investigations/es0810/es0810page03
.cfm
Volcanic Eruptions
Volcano Anatomy
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Magma Chamber magma collected inside a
volcano pocket
Pipe - a long tube that
connects the magma
chamber to Earth's
surface.
Vent - an opening
through which the magma
leaves the volcano
Crater - a bowl-shaped
area around a volcano's
central vent.
Lava Flow – an area
covered by lava as it flows
out of the vent
As magma rises toward the surface, the
dissolved gas begins to expand as
pressure decreases and this exerts an
enormous upward force on the magma.
When a volcano erupts, the force of the
expanding gases pushes magma from
the magma chamber through the pipe
until it flows or explodes out of the
vent.
http://education-portal.com/academy/lesson/volcanic-landforms-types-formation.html
Kinds of Volcanic Eruptions
1.
2.
Quiet
Explosive
Type depends on
1. Magma’s silica content
2. Thin and runny/ thick and sticky magma
3. Gas content
Silica – material found in magma that is
formed from oxygen and silicon
Quiet Eruptions
1.
2.
3.
4.
Low silica magma
Magma is thin, runny, flows easily
Gases bubble gently
Oozes quietly from the vent and flows
Hawaiian Islands formed from quiet eruptions
https://www.youtube.com/watch?v=488BkTUsMa
4
Quiet eruptions produce two different types of
lava –
Pahoehoe –
Hot, fast moving, thin and runny
Looks like rope like coils
https://www.youtube.com/watch?v=eoPz5O6_-d0
Aa –
Cooler, slow moving, thicker
than pahoehoe.
Forms jagged lava chunks
https://www.youtube.com/watch?v=vnWcStAL35Y
Explosive Eruptions
1.
2.
High silica magma
Thick and sticky
Lava has different size particles a. Volcanic ash – fine, rocky,
(speck of dust or flour)
b. Cinders – pebble sized
c. Bombs – size of a baseball to
a car
Pyroclastic Flow
• Pyroclastic Flow -an explosive fast-moving current of hot
gas and rock (1800 0F/6500c) hurls out ash, cinders, and
bombs.
Rocks formed during explosive eruptions –
1. Obsidian – lava cools quickly, smooth surface
2. Pumice – fast cooling lava with bubbles
trapped in, leaving spaces
Mt. St. Helen’s Eruption
May 18, 1980 eruption triggered 5.1 earthquake
 57 People killed
 7,000 big game animals, 12 million Chinook and
Coho salmon, and millions of birds and small
mammals are believed to have died
 $1.1 billion in property damages for timber loss, etc.
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https://www.youtube.com/watch?v=WEhW
1jEu9Tg
Mt Vesuvius & Pompeii, Italy
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Erupted in 79 AD, approximately 20,000 people were killed in
this eruption
Pompeii is buried & is covered in a pyroclastic flow of cinders,
ash, and mud around 20 feet high.
Active, Dormant or Extinct?
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active volcano - is one that is erupting or has shown
signs that it may erupt in the near future.
Mt. Shasta (1700s) and Lassen Peak (1915, 1921) in CA
dormant volcano is not active now but may become
active in the future.
 extinct volcano is unlikely to erupt again
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Landforms from Lava and Ash
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Shield Volcanoes
Cinder Cone
Composite Volcanoes
Lava Plateaus
Shield Volcanoes
 Composed
mainly of
runny lava flows
 Wide, gently sloping
mountains
 Largest volcanoes in
the world
 An example:
Hawaiian Islands
 Gentle slopes &
domed shaped
http://dli.taftcollege.edu/streams/geography/Animations/Volcano
Types.html
Cinder Cone Volcanoes
Made mostly of cinders
and other rock particle
 Little or no lava flows
 Formed from explosive
type volcanoes (high
silica)
 Narrow base and steep
sides
 Example: Black Butte in
Northern Calif.
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Composite Volcanoes
 Tall,
cone shaped
mountains. Built up of
alternating layers of ash
and lava
 Examples: Mt. Vesuvius
in Italy, Mt St. Helens,
Mt Shasta, Mt Lassen
Lava Plateaus
Layers of thin, runny lava flow and solidify on top
of earlier layers.
Columbia Plateau in Washington, Idaho, and
Oregon
Soils from Lava and Ash
Volcanic ash releases potassium and
phosphorous that plants need. Volcanic
soil is fertile.
Volcanic Landforms: Calderas
Huge hole left by the collapse of a volcanic
mountain
 An enormous eruption may empty a volcano's
main vent and magma chamber. With nothing
to support it, the top of the mountain collapses
inward.
 Yellowstone in Wyoming, Crater Lake in Oregon
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http://dli.taftcollege.edu/streams/
geography/Animations/Caldera.ht
ml
Yellowstone Caldera is huge!!
34 miles x 45 Miles
Whole caldera is slowly rising
causing lake to tilt & run
toward southeast
Landforms from Magma
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Volcanic Neck - magma hardens in a
volcano's pipe. The softer rock around the pipe
wears away, exposing the hard rock of the
volcanic neck.
A sill forms when magma squeezes between
horizontal layers of rock and hardens.
 Dike
– a vertical column of
cooled magma that forms
when magma intrudes
(forces itself) across rock
layers and hardens.
Sills and dikes are intrusions – an intrusion is
always younger than the rock around it.
Batholith -a large body of magma cools
inside the crust, a mass of rock