Transcript Chapter 9 Volcanoes

Chapter 9 Volcanoes
Section 1 Volcanic Eruptions
Volcano – a mountain that forms when
molten rock, called magma, is forced to
the Earth’s surface.
Nonexplosive Eruptions
Lava – magma that flows onto Earth’s
surface.
Lava flows are associated with
nonexplosive eruptions.
Explosive Eruptions
Clouds of hot debris and gases shoot out
from the volcano
Volcano may actually
decrease in size.
Cross Section of a Volcano
Lava
Vent
Magma
Chamber
Magma
The composition of the magma determines
the explosiveness of the volcano.
Water content
More water = more
explosion
Example: Soda Can
Silica Content
More silica = slow
flowing magma
(high viscosity)
Discovery: Volcano
What erupts from a Volcano?
Lava:
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Blocky Lava
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Pahoehoe
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Aa
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Pillow Lava
What erupts from a Volcano?
Pyroclastic Material – the rock fragments
created by a volcanic eruption.
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Volcanic Blocks
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Volcanic Bombs
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Lapilli
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Volcanic Ash
Section 2 Volcanoes’ Effects on
Earth
An Explosive Impact –
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Ashe – high into atmosphere – blocks sunlight
Makes it hard to breathe
Blocks roads
Flows and Fallout
Lahar – a mixture of mud, groundwater,
flowing at a rapid speed down the
mountain after an eruption.
Pyroclastic Flows
Rapidly flowing clouds of
hot ash and volcanic
glass rolling down the
mountainside.
Can cut down houses,
trees, block roads, and
devastate river valleys.
Climatic Changes
Volcanic ash and sulfuric gases can reach
the upper atmosphere.
These gases can affect the amount of
sunlight reaching the ground.
Mount Pinatubo, 1991
Average global temperatures
dropped as much as 0.5 degrees
Celsius.
Three Types of Volcanoes
Shield – built by repeated
nonexplosive eruptions where
lavaflows slowly build the
mountain.
Cinder Cone – small
volcanoes made from
pyroclastic materials of
moderately explosive
eruptions.
Composite (Stratovolcanoes)
– explosive eruptions followed
by outpourings of lava.
Layered Volcano
Craters and Calderas
Crater – funnel
shaped pit at top of
the volcano
Caldera – when a
magma chamber
empties and the roof
collapses.
Lava Plateaus
Large layers of lava flowing from fissures
in the ground. Columbia River Plateau
Section 3 - What Causes Volcanoes?
The Formation of Magma
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In the lower crust / upper mantle large
reservoirs of magma form.
Pressure / Temperature – affect magma
formation
Density – magma rises because it is less
dense than the surrounding rock.
Ring of Fire
Boundary around the Pacific Plate – 75%
of the world’s active volcanoes.
Hot Spot Volcanoes
An isolated volcano not caused by
movement at a plate boundary, but rather
by the melting of a mantle plume.