Volcanoes and Igneous Activity Earth - Chapter 4

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Chapter 10
Volcanoes and Other Igneous Activity
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10.1 The Nature of Volcanic Eruptions
? Factors that determine the violence of an
eruption



? Viscosity
____________is the measure of a material's
resistance to flow.
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10.1 The Nature of Volcanic Eruptions
? Viscosity
Factors affecting viscosity
- Temperature (_____________________)
- Composition (_______________)

1. High silicahigh viscosity (e.g., rhyolitic
   lava)

2. Low silicamore fluid (e.g., basaltic lava)
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10.1 The Nature of Volcanic Eruptions

• Dissolved gases

Mainly ___________ and _____________
Gases expand near the surface
A _________ is an opening in the surface of
Earth through which molten rock and gases are
released.
Provide the force to extrude lava
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10.1 The Nature of Volcanic Eruptions

• Dissolved gases

Violence of an eruption is related to how
easily gases escape from magma
- Gases escape easily from ____________.
- ____________magma produces a more violent
eruption.
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Magma Composition
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10.1 The Nature of Volcanic Eruptions

• Lava Flows

Basaltic lavas are more ____________.
Types of lava
- _______________ (resembles braids in ropes)
- ___________ (rough, jagged blocks)

• Gases

One to 5 percent of magma by weight
Mainly water vapor and carbon dioxide
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Pahoehoe (Ropy) Lava Flow
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Slow-Moving Aa Flow
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10.1 The Nature of Volcanic Eruptions

• Pyroclastic Materials

Pyroclastic materials is the name given to
_____________produced in volcanic eruptions.
The fragments ejected during eruptions range
in _________ from very fine dust and volcanic ash
(less than 2 millimeters) to pieces that weigh
several tons.
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10.1 The Nature of Volcanic Eruptions

• Pyroclastic Materials

Types of pyroclastic material
- ____________fine, glassy fragments
- ________frothy, air-filled lava
- _______walnut-sized particles
- ______pea-sized particles
Particles larger than lapilli
- _________hardened lava
- __________ejected as hot lava
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10.1 The Nature of Volcanic Eruptions

• The three main volcanic types are

• Anatomy of a Volcano

A volcano is a mountain formed of lava and/or
pyroclastic material.
A crater is the _________ at the ___________
of a volcano or that which is produced by a
________________.
A conduit, or pipe, carries gas-rich magma to
the surface.
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Anatomy of a Typical Volcano
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10.1 The Nature of Volcanic Eruptions

• Shield Volcanoes

Shield volcanoes are.

• Cinder Cones

Cinder cones are ________ volcanoes built
primarily of ___________________________________
- ___________ angle
- Rather small in size
- Frequently occur in _______
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Shield Volcanoes
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Cinder Cones
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10.1 The Nature of Volcanic Eruptions

• Composite Cones

Composite cones are volcanoes composed of
_______________________________
- Most are adjacent to the ______________
(e.g., Mt. Rainier).
- ____________ size
- ____________________ lavas and pyroclastics
- Most violent type of activity
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Composite Cones
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Mount St. Helens Before and After the May 18,
1980, Eruption
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Profiles of Volcanic Landforms
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10.1 The Nature of Volcanic Eruptions

• Calderas

Calderas are large ____________ in volcanoes.
Nearly circular
Formed by __________________
Size exceeds ____________________
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10.1 The Nature of Volcanic Eruptions

• Lava Plateaus

Fluid basaltic lava extruded from crustal
fractures called fissures.
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10.2 Intrusive Igneous Activity

• Plutons are intrusive igneous structures that
  result from the cooling and hardening of magma
  beneath the surface of Earth.

Intrusive igneous bodies, or plutons, are
generally classified according to their ________,
________, and ____________________________________
_
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10.2 Intrusive Igneous Activity

• Sills and Laccoliths

Sills and laccoliths are plutons that form
when magma is intruded close to the surface.
-_____________resemble buried lava flows and may
exhibit _____________ joints.
- Laccoliths are ___________________masses that
arch overlying strata upward.
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Sills
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10.2 Intrusive Igneous Activity

• Dikes

Dikes are tabular-shaped intrusive igneous
features that cut across preexisting rock layers.
Many dikes form when magma from a large magma
chamber invades fractures in the surrounding
rocks.
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10.2 Intrusive Igneous Activity

• Batholiths

Batholiths are large masses of igneous rock
that formed when magma intruded at depth, became
crystallized, and subsequently was exposed by
erosion.
An intrusive igneous body must have a surface
exposure ______________________to be considered a
batholith.
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Batholiths
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Types of Igneous Plutons
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10.2 Intrusive Igneous Activity

• Geologists conclude that magma originates when
  essentially solid rock, located in the crust and
  upper mantle, partially melts.

• The most obvious way to generate magma from solid
  rock is to raise the temperature above the level
  at which the rock begins to melt.

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10.2 Intrusive Igneous Activity

• Role of Heat

The geothermal gradientEarths natural
temperature increases with depth but is not
sufficient to melt rock in the lower crust and
upper mantle
Additional heat is generated by
- ___________________________
- ____________________________
- __________________________
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10.2 Intrusive Igneous Activity

• Role of Water

Causes rock to melt at a ______________
Plays an important role in subducting ocean
plates
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Basaltic Magma at the Surface
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10.3 Plate Tectonics and Igneous Activity

• The basic connection between plate tectonics and
  volcanism is that plate motions provide the
  mechanisms by which mantle rocks melt to generate
  magma.

• __________________

Rising magma can form ________________in an
ocean (Aleutian Islands).

• Ocean-Continent

Rising magma can form ____________________(Ande
s Mountains).
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Convergent Boundary Volcano
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10.3 Plate Tectonics and Igneous Activity

• The greatest volume of volcanic rock is produced
  along the oceanic ridge system.

Lithosphere ________________.
Less pressure on underlying rocks
Partial melting occurs
Large quantities of ___________________are
produced.
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10.3 Plate Tectonics and Igneous Activity

• Intraplate volcanism is igneous activity that
  occurs within a tectonic plate away from plate
  boundaries.

Most intraplate volcanism occurs where a mass
of hotter than normal mantle material called a
__________________rises toward the surface.
The activity forms localized volcanic regions
called ___________________.
Examples include the ___________________and
the Columbia Plateau.
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Kilauea, an Intraplate Volcano