Transcript Ch 10 Fall 2014

STARTER 12-1-14
1. Describe how Hawaii was formed by Hot
Spots.
2. Describe how Oceanic-Oceanic
convergent boundaries create volcanism.
3. Describe how a Continental Volcanic Arc
is formed.
10 The Nature of Volcanoes
Objectives
P. 78
Today you will be able to describe:
•
•
•
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What determines the type of volcanic eruption?
What materials are ejected from volcanoes?
What are the three main types of volcanoes?
What other landforms are associated with volcanic eruptions?
10 The Nature of Volcanoes
• Volcanic eruptions are windows to Earth’s
interior.
−Provide opportunities to observe processes deep beneath
Earth’s surface
•Why are some volcanic eruptions explosive, while others are quiet?
10 The Nature of Volcanoes
 Factors that determine the violence of an
eruption
• Composition of the magma
• Temperature of the magma
• Dissolved gases in the magma
List-Group-Label: Volcanoes
10 The Nature of Volcanoes
 Viscosity
• Viscosity is a material's resistance to flow.
• Ie. Syrup, water, oil
• Factors affecting viscosity
- Temperature (hotter magmas are less viscous)
- Composition (silica content)
1. High silica—high viscosity
(e.g., flows slowly)
2. Low silica—low viscosity(e.g., flows quick)
10 The Nature of Volcanoes
 Dissolved gases
• Mainly water vapor and carbon dioxide
• Gases expand near the surface:
• trapped in magma and provide the force
to extrude molten rock at surface
• A vent is an opening in the surface through
which molten rock and gases are released.
10 The Nature of Volcanoes
 Dissolved gases
• Violence of an eruption is related to how easily
gases escape from magma
-Gases escape easily from fluid magma.
- Quiet eruption
-Viscous (thick) magma slows the upward movement
- more violent eruption.
10 The Nature of Volcanoes
 Lava Flows
• Varying flow rates
• Flow rate – speed at which it moves
•Dependent upon composition of material
10 The Nature of Volcanoes
 Gases
•Volcanic gases contribute greatly to our atmosphere
•Volcanic eruptions are:
•70% water vapor
•15% CO2
•5% N
•5% S
•Trace amounts of Cl, H, Ar
(Ropy) Lava Flow
Slow-Moving Aa Flow
(jagged edges)
10 The Nature of Volcanoes
 Pyroclastic Materials
• Pyroclastic materials name given to particles
produced in volcanic eruptions.
• The fragments ejected during eruptions range in
size from very fine dust and volcanic ash to very
large.
10 The Nature of Volcanoes
 Pyroclastic Materials
• Types of pyroclastic material
•Small Particles
- Ash and dust—fine, glassy fragments
- Cinders—pea-sized particles
• Larger Particles
- Blocks—hardened lava
- Bombs—ejected as hot lava
10 Types of Volcanoes
Objectives
P. 80
Today you will be able to describe:
• What are the three main types of volcanoes?
• What other landforms are associated with volcanic eruptions?
Starter 12/2/14
1. Volcanic eruptions can lead to changes in the local climate.
•
Describe how escaping gases can cause a change in climate.
•
How can it cause air pollution.
2. When viewing magma/lava it gives us an observation as to
what is taking place in the mantle.
•
Give your description how this is possible.
10 Types of Volcanoes
 Types of Volcanoes
 The three main volcanic types have their
own volcanic history.
•More than 26 different types of volcanoes.
10 Types of Volcanoes
 Anatomy of a Volcano
• Begin as a fissure or crack in the crust
• Magma forces it way to surface under pressure
• A volcano is a mountain formed of lava and/or
pyroclastic material.
• A crater is the depression at the summit of a
volcano
• A conduit, or pipe, carries gas-rich magma to the
surface.
Anatomy of a “Typical” Volcano
10 Types of Volcanoes
 Shield Volcanoes
• Shield volcanoes are broad, gently sloping
volcanoes built from fluid lavas.
• Grow from the ocean floor to form islands
Shield Volcanoes
10 Types of Volcanoes
 Cinder Cones
• Cinder cones are small volcanoes built primarily
of pyroclastic material ejected from a single vent.
• May last weeks to years
• Once stops erupting never erupts again
- Steep slope angle
- Rather small in size
- Frequently occur in groups
Cinder Cones
Composite Cones
10 Types of Volcanoes
 Composite Cones
• Composite cones(stratovolcanoes) composed
of both lava flows and pyroclastic material.
- Most are adjacent to the Pacific Ocean
- Most active region is Northern and Western
Pacific
- Large size
- Most violent type of activity
Mount St. Helens Before and
After the May 18, 1980, Eruption
10 Types of Volcanoes
 Calderas
• Calderas are large depressions in volcanoes.
• Nearly circular
• Formed by collapse
10 Types of Volcanoes
 Necks and Pipes
•Volcanoes are fed through a conduit called a pipe.
•Pipe is connected to the magma chamber
•Cinder cone volcanoes are easily eroded
•Sometimes leaving crystallized magma behind
known as a neck
10 Types of Volcanoes
 Lava Plateaus
• low viscosity lava flows covering a wide area.
10 Types of Volcanoes
 Plutons are intrusive igneous structures
that result from the cooling and hardening
of magma.
• are generally classified according to their shape,
size, and relationship to the surrounding rock
layers.
10 Types of Volcanoes
 Role of Heat
• The geothermal gradient—Earth’s natural
temperature increases with depth but is not
sufficient to melt rock in the lower crust
and upper mantle
• Additional heat is generated by
- friction in subduction zones
- crustal rocks heated during subduction
- rising, hot mantle rocks
• http://www.tulane.edu/~sanelson/Natural_
Disasters/volclandforms.htm
10.2 Intrusive Igneous Activity
 Sills and Laccoliths
• Sills and laccoliths are plutons that form when
magma is intruded close to the surface.
- Sills resemble buried lava flows and may
exhibit columnar joints.
- Laccoliths are lens-shaped masses that arch
overlying strata upward.
Sills
Sill
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.
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 greater than 100 square kilometers to
be considered a batholith.
Batholiths
Types of Igneous Plutons
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.
10.2 Intrusive Igneous Activity
 Role of Water
• Causes rock to melt at a lower temperature
• Plays an important role in subducting
ocean plates
Basaltic Magma at the Surface
STARTER 03/24/11
• Answer the reading checkpoint questions
on page 290 and 291.
10.2 Review
1. Is the following sentence true or false?
Plutons can be studied on Earth’s surface
as they form.
2. What three characteristics are used to
classify intrusive igneous bodies?
3. when magma from a large
magma chamber invades
fractures in the surrounding
rocks
4. when a large intrusive igneous
body of greater than 100 km2
accumulates and becomes
exposed
5. when magma is injected
between sedimentary layers
close to Earth’s surface and
collects as a lens-shaped
mass
6. when magma is injected along
sedimentary bedding surfaces
close to Earth’s surface
a. Sill
b. Laccolith
c. Batholith
d. dike
7. Is the following sentence true or false? Magma
forms when solid rock in the crust and upper
mantle partially melts.
8. Circle the letter of one way magma is
generated.
a. The confining pressure of rocks is increased.
b. The water content of rocks is reduced.
c. The temperature of rocks is lowered below
their melting points.
d. The temperature of rocks is raised above
their melting points.
9. The rate at which temperature changes
with depth below Earth’s surface is called
the _______________.
10. How is decompression melting of rocks
triggered?
11. ______________rock buried at depth
has a much lower melting temperature
than does ______________ rock of the
same composition and under the same
pressure.
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.
 Ocean-Ocean
• Rising magma can form volcanic island arcs in
an ocean (Aleutian Islands).
 Ocean-Continent
• Rising magma can form continental volcanic arcs
(Andes Mountains).
Convergent Boundary Volcano
10.3
Plate Tectonics and Igneous Activity
 The greatest volume of volcanic rock is
produced along the oceanic ridge system.
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•
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Lithosphere pulls apart.
Less pressure on underlying rocks
Partial melting occurs
Large quantities of fluid basaltic magma are
produced.
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
mantle plume rises toward the surface.
• The activity forms localized volcanic regions
called hot spots.
• Examples include the Hawaiian Islands and the
Columbia Plateau.
Kilauea, an Intraplate Volcano
STARTER
• Complete Map Master Skills Activiy on
page 296