ESC 1000 Earth and Space Science Video Lecture Notes
Name: ________________
Earth Revealed #13: Volcanism (1992)
Please watch the video in
class. Take notes on the Earth Revealed Disc #13 Volcanism circle each of the Chapter
9 vocabulary words discussed in the video. When the film is finished and after
reading Chapter 9 write questions with answers that a
student should be able to answer if she/he viewed this video. You should have
at least two or more questions for each chapter. List the most significant discovery
you made about Volcanoeswhich you did not know before
watch the film.
Play Video: http://www.learner.org/resources/series78.html
Chapter 9: Volcanoes and Other Igneous Activity
Ch. 9: Volcanoes and Other Igneous Activity
After reading and studying Ch. 9, you
should be able to:
Concept
1: List the factors that contribute to and
determine the violence of volcanic eruptions.
Concept
2: Describe the various types of volcanoes and
other features produced by volcanic activity including materials extruded and
hazards associated with eruptions.
Concept
3: List and describe several intrusive igneous
features.
Concept
4: Discuss the role of heat, pressure, and
composition (including volatiles) in the origin of magma.
Concept
5: Describe the relationship between igneous
activity and plate tectonics
The following statements summarize and describe many of the key terms and
concepts presented in the chapter.
- The primary factors
that determine the nature of volcanic eruptions include the magma's temperature,
its composition, and the amount of dissolved gases
it contains. As lava cools, it begins to congeal, and as viscosity
increases, its mobility decreases. The viscosity of magma is
directly related to its silica content. Rhyolitic
lava, with its high silica content, is very viscous and forms short, thick
flows. Basaltic lava, with a lower
silica content, is more fluid and may travel a long distance before
congealing. Dissolved gases provide the force that propels molten rock
from the vent of a volcano.
- The materials associated with a
volcanic eruption include lava flows (pahoehoe
and aa flows for basaltic lavas), gases
(primarily in the form of water vapor), and pyroclastic material
(pulverized rock and lava fragments blown from the volcano's vent, which
include ash, pumice, lapilli, cinders,
blocks, and bombs).
- Successive eruptions of lava
from a central vent result in a mountainous accumulation of material known
as a volcano. Located at the summit of many volcanoes is a
steep-walled depression called a crater.
Shield cones are broad, slightly domed volcanoes built
primarily of fluid, basaltic lava. Cinder cones have steep
slopes composed of pyroclastic material. Composite
cones, or stratovolcanoes,
are large, nearly symmetrical structures built of interbedded
lavas and pyroclastic deposits. Composite cones
produce some of the most violent volcanic activity. Often associated with
a violent eruption is a nuée
ardente, a fiery cloud of hot gases
infused with incandescent ash that races down
steep volcanic slopes. Large composite cones may also generate a type of
mudflow known as a lahar.
- Most volcanoes are fed by conduits
or pipes. As erosion progresses, the rock occupying the pipe
is often more resistant and may remain standing above the surrounding
terrain as a volcanic neck. The summits of some volcanoes
have large, nearly circular depressions called calderas that
result from collapse following an explosive eruption. Calderas also form
on shield volcanos by subterranean drainage from
a central magma chamber, and the largest calderas form by the discharge of
colossal volumes of silica-rich pumice along ring fractures. Although
volcanic eruptions from a central vent are the most familiar, by far the
largest amounts of volcanic material are extruded from cracks in the crust
called fissures. The term flood basalts
describes the fluid, waterlike, basaltic lava
flows that cover an extensive region in the northwestern United States
known as the Columbia Plateau. When silica-rich magma is extruded, pyroclastic flows
consisting largely of ash and pumice fragments usually result.
- Igneous intrusive bodies are
classified according to their shape and by their orientation
with respect to the host rock, generally sedimentary rock. The two
general shapes are tabular (tablelike)
and massive. Intrusive igneous bodies that cut across
existing sedimentary beds are said to be discordant, whereas
those that form parallel to existing sedimentary beds are concordant.
- Dikes are tabular, discordant igneous
bodies produced when magma is injected into fractures that cut across rock
layers. Tabular, concordant bodies called sills form when
magma is injected along the bedding surfaces of sedimentary rocks. Laccoliths
are similar to sills but form from less-fluid magma that collects as a
lens-shaped mass that arches the overlying strata upward. Batholiths,
the largest intrusive igneous bodies with surface exposures of more than
100 square kilometers (40 square miles), frequently make up the cores of
mountains.
- Magma originates from
essentially solid rock of the crust and mantle. In addition to a rock's
composition, its temperature, depth (confining pressure), and water
content determine whether it exists as a solid or liquid. Thus, magma can
be generated by raising a rock's temperature, as occurs when
a hot mantle plume "ponds" beneath crustal
rocks. A decrease in pressure can cause decompression melting.
Further, the introduction of volatiles (water) can lower a
rock's melting point sufficiently to generate magma. Because melting is
generally not complete, a process called partial melting
produces a melt made of the lowest-melting-temperature minerals, which are
higher in silica than the original rock. Thus, magmas generated by partial
melting are nearer to the granitic (felsic) end of the compositional spectrum than are the
rocks from which they formed.
- Most active volcanoes are
associated with plate boundaries. Active areas of volcanism are
found along oceanic ridges where seafloor spreading is occurring (divergent
plate boundaries), in the vicinity of ocean trenches where one
plate is being subducted beneath another (convergent
plate boundaries), and in the interiors of plates themselves (intraplate volcanism).
Rising plumes of hot mantle rock are the source of most intraplate volcanism.
·
Earth Revealed #13. Volcanism
Volcanoes provide clues about what is going on inside Earth. Animations illustrate
volcanic processes and how plate boundaries are related to volcanism. The
program also surveys the various types of eruptions, craters, cones and vents,
lava domes, magma, and volcanic rock. The 1980 eruption of Mount
St. Helens serves as one example.
Play Video: http://www.learner.org/resources/series78.html
Video Notes:
Chapter 9: Volcanoes and Other
Igneous Activity
AA flow
|
Furmarole
|
Pyroclastic Flow
|
Batholith
|
Geothermal Gradient
|
Pyroclastic Material
|
Caldera
|
Hot Spot
|
Scoria Cone
|
Cinder Cone
|
Intraplate Volcanism
|
Shield Volcano
|
Columnar Joint
|
Island Arc
|
Sill
|
Composite Cone
|
Laccolith
|
Strato volcanoes
|
Conduit
|
Lahar
|
Vent
|
Continental Volcanic Arc
|
Mantle Plume
|
Viscosity
|
Crater
|
Muee Ardente
|
Volatiles
|
Decompression Melting
|
Pahoehoe Flow
|
Volcanic Island
Arc
|
Dike
|
Parasitic Cone
|
Volcanic Neck
|
Fissure
|
Partial Melting
|
Volcano
|
Fissure eruption
|
Pipe
|
|
Flood basalt
|
Pluton
|
|
Student Questions (with Answers):
1.
2.
3.
Most Significant Discovery (discoveries):
Video Study Guide: Earth Revealed
Episode 13: Volcanism
Why does magma rise to the
surface?
Where
are most of the world's active volcanoes?
What is pillow lava?
Describe the Hawaiian hotspot.
Describe basaltic (mafic) magma and why it commonly forms shield
volcanoes.
What are rift zones?
Why are the volcanoes around the Pacific rim called composite
volcanoes?
What common gasses occur in composite (intermediate)
magmas?
What factors influence the explosiveness of volcanoes?
Discuss andesitic (intermediate) magmas associated
with composite volcanoes.
Describe pumice and how it is formed.
Discuss viscosity and how it relates to the formation of pahoehoe and aa
lavas.
How do lava tubes form?
Describe cinder cones and how they differ from composite and shield
volcanoes.
What tectonic
settings are most volcanoes associated with?
What is obsidian and how is it formed?
Discuss the clues that volcanologists use to
predict eruptions.
Discuss how volcanoes relate to ore deposits and geothermal energy.
What are some of the beneficial aspects of volcanoes?