Geoscience Reference
In-Depth Information
VISUAL CONCEPT CHECK
13.3
Given your understanding of volcanoes,
describe the volcano pictured here. Is it a
cinder-cone, composite, or shield volcano?
How can you tell? What kind of eruption will
most likely occur when it does erupt?
A
mudpot
consists of a bubbling mixture of gaseous mud and
water. These systems form where hot water is limited and hy-
drogen sulfide gas is present, creating sulfuric acid. This acid
dissolves the surrounding rock into fine particles of silica and
clay that mix with what little water there is to form the mudpot.
A
fumerole
is a steam vent that results because underlying
groundwater is boiled away before reaching the surface.
rises through cracks in overlying continental crust. The
Cascade volcanic arc is an example of this relationship.
3.
Volcanic eruptions can be broadly classified as explosive
or fluid. Explosive eruptions occur when the magma is vis-
cous, forming composite volcanoes (also called stratovol-
canoes) such as those in the Cascades. When the magma
is not viscous, it flows freely, resulting in broad rivers of
lava that collectively form shield volcanoes such as those
in the Hawaiian Islands. Cinder-cone volcanoes evolve
through the accumulation of solidified magma fragments,
rock debris, and ash that are ejected from a central vent.
KEY CONCEPTS TO REMEMBER ABOUT
VOLCANOES
1.
Volcanoes occur most frequently on plate boundaries.
In particular, most of the world's volcanoes are found
along the Pacific Ring of Fire.
4.
Some volcanoes form over hotspots, which are places
where upwelling magma reaches the surface. Examples
of hotspot activity are the Hawaiian Islands and Yellow-
stone National Park.
2.
Volcanoes are most frequently associated with the pro-
cess of subduction because oceanic crust melts and then
mudpot
A bubbling mixture of gaseous mud and water at the
Earth's surface that is associated with geothermal activity.
fumerole
A steam vent that results because underlying
groundwater is boiled away before reaching the surface.
Volcanoes
Now that we have discussed volcanoes thoroughly, you can
see their associated processes in animated form. Go to the
Geo Media Library
and access
Volcanoes
. This animation
contains a video that compares shield and composite vol-
canoes and shows various examples of each kind. As you
watch the video, note how the concept of plate tectonics
fits into the evolution of volcanoes, where they occur, and
how they erupt. After you complete the animation, be sure to
answer the questions at the end to test your understanding
about volcanoes.
S u m m a r y o f K e y C o n C e p t S
1.
The Earth's crust is not a single sheet, but rather a jigsaw
puzzle of interconnected plates. A variety of evidence
(location of fossil remains, apparent magnetic polar
wander, and actual measurement of motion) strongly
supports the theory of continental drift, indicating that
plates have shifted through geologic time.
