Introduction
Volcano Definition
-An Opening in the Earth’s crust through
which magma reaches the surface.
-Most often occur along plate boundaries
Magma vs. Lava
Magma vs. Lava
Lava-
Magma-
Hot, molten or semi-molten rock located under ground.
Hot, molten or semi-molten rock that has reached the surface.
•Different than magma in that most of the gasses have escaped
•Two types of lava, Aa and Pahoehoe
Magma typically consists of:
- a liquid portion (often referred to as the melt)
- a solid portion made of minerals that crystallized directly from the melt
- solid rocks incorporated into the magma from along the conduit or
reservoir, called xenoliths or inclusions
- dissolved gases
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Magma vs. Lava
Aa Lava
Aa Lava-
lava with a rough rubbly surface composed of broken lava blocks called
clinkers.
•Aa lava forms when
lava has cooled and
it’s viscosity
has been increased.
Aa Lava
Aa Lava
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Aa Lava
Pahoehoe Lava
Pahoehoe Lava- lava that has a smooth, hummocky, or ropy surface. A
pahoehoe flow typically advances as a series of small lobes and toes that
continually break out from a cooled crust.
•The surface texture of pahoehoe flows varies widely, displaying all kinds of bizarre
shapes. Click images to view.
Coil
Entrial
Toe
Ropy
Clinker
Pahoehoe Lava
Types of Lava Movie
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Lava Formations
Lava Formations
Tree molds are formed when lava surrounds
a tree, chills against it, and then drains away.
The standing structure left behind is often
called a lava tree.
Hornito
A small spatter cone that forms on the surface of
a lava flow (usually pahoehoe) is called a hornito.
A hornito develops when lava is forced up through
an opening in the cooled surface of a flow and then
accumulates around the opening. Typically, hornitos are
steep sided and form conspicuous pinnacles or stacks.
Tree trunks engulfed and incinerated by lava
leave cylindrical hollows, or tree molds,
where lava solidified against them; tree
molds often preserve the original surface
texture of the tree. Tree molds are found
within standing lava trees and on the
surfaces of lava flows. They are common in
Pahoehoe flows.
Lava Trees and Tree Molds
Lava Formations
Pele’s Hair
A naturally spun volcanic glass that
is blown away from lava fountains,
cascading lava falls, or turbulent lava flows.
Pele's hair is gold in color and has a
diameter of less than half a millimeter.
Lava Formations
Pele’s Tears
Kipuka
Small bits of molten lava in fountains can
cool quickly and solidify into glass particles
shaped like spheres or tear drops called Pele's
tears, named after Pele, the Hawaiian goddess
of volcanoes. They are jet black in color and
are often found on one end of a
strand of Pele's hair.
A small piece of land is completely
surrounded by lava flows
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Lava Tubes
L
a
v
a
A natural conduits through which lava travels beneath the
surface of a lava flow. Tubes form by the crusting over of
lava channels and pahoehoe flows.
F
o
r
m
a
t
i
o
n
s
Skylight
Lava Tubes
An opening in the roof of
a lava tube.
Lava Formations
Catching Lava
Lava Bench
A platform formed by new lava flows that extends
the old shoreline; in particular, this can be
observed on Hawaii at Kilauea volcano during
times when lava is entering the ocean, forming
new land. In their young stadium, benches are
highly unstable. They often are underlain only by
loose material such as sand and wave-eroded
rock. Young benches can collapse at any time,
and it is life-threatening to stand on one.
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Volcanic Settings
-Rift Eruptions
Divergent Boundaries
• The greatest volume of volcanic rock is produced
along the oceanic ridge system
• Lithosphere pulls apart
• Less pressure on underlying rocks
• Large quantities of fluid basaltic magma are
produced
-Hot Spots
Subduction Boundaries
Divergent Boundaries
The long sheets of lava are
known as a “Curtain of Fire”
Convergent (Subduction) Boundaries
- Plate motions provide the mechanism by which mantle rocks melt to form
magma
• Convergent plate boundaries
• Descending plate partially melts
• Magma slowly rises upward
• Rising magma can form
• Volcanic island arcs in an ocean (Aleutian Islands)
• Continental volcanic arcs (Andes Mountains)
On Land Divergent Boundaries
Will give us Rift Eruptions
Click to view
an animation
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Subduction Boundary Movie
Hot Spots
• Intraplate igneous activity
• Activity within a rigid plate
• Plumes of hot mantle material rise
• Form localized volcanic regions called hot
spots
Types of Volcanoes
Shield Volcanoes
•Formed over a series of eruptions
•Shaped like a shield
•Mauna Loa, 6 miles high, 70 miles wide
•Made from mafic magma
•Low in quartz
•Low viscosity
•Low gas content
•Mild eruptions
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Shield Volcano Movie
CCHS Earth Science Hawaii ‘05
CCHS Earth Science Hawaii ‘05
CCHS Earth Science Hawaii ‘05
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CCHS Earth Science Hawaii ‘05
CCHS Earth Science Hawaii ‘05
Walking Very Carefully
Abby Brewer Sampling Lava
Mauna Loa
CCHS Earth Science Hawaii ‘05
CCHS Earth Science Hawaii ‘05
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CCHS Earth Science Hawaii ‘05
CCHS Earth Science Hawaii ‘05
Kilauea Crater
Kilauea Iki
Composite (Strato)Volcano
Composite (Strato)Volcano
•“Classic Volcanic Shape”
•Taller than wide
•St. Helens, Fuji, Tambora
•Made from felsic magma
•High in quartz
•High viscosity
•High gas content
•Violent eruptions
Click to flyover a
composite volcano
Satellite Image of Mt. Fuji
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Composite (Strato) Volcano
Cinder Cone
•Made up of loose material - ash
•Steep Slopes (angle of repose)
•1000-1500 feet (small)
•Mild eruptions
•Paricutin, Mexico
Red Cinder Cone Above the Clouds
Paricutin Cinder Cone
•February 20th, 1943
•Sees smoke coming from his corn field
•Volcano growing out of no where
•Small hole with sulfurous
gasses coming out
Farmer Dionisio Pulido
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Paricutin Cinder Cone
Paricutin Cinder Cone
•At night, glowing rocks thrown into air
•Eruptions end 12 years later, 1955
•After 1 year reaches 1100 feet
•Town is buried
•Lava then begins to flow out the sides
•First deaths result in 1957….why???
•Covers neighboring village
•Boundary disputes
Paricutin Cinder Cone Movie
A size comparison of the three
types of volcanoes
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The End
….for now
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