11.2B Folds, Faults, and Mountains
Mountains,
Plateaus,
Domes
and
Basins
Types of Mountains
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Folding and faulting produce many
but not all of Earth’s mountains.
In general, mountains are classified
by the processes that formed them
The major types of mountain types
include
 Volcanic mountains
 Folded mountains
 Fault-block mountains
 Dome mountains
Mountain Ranges
Types of Mountains :
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Geologists refer to the collection
of processes involved in mountain
building as orogenesis. The term is
derived from the Greek oros
meaning “mountain” and the –geny
meaning “born”.
Earth’s mountains do not occur at
random. Several mountains of
similar shape, age, size and
structure form a group called a
mountain range.
Mountain Systems
Types of Mountains :
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A group of different mountain
ranges in the same region form a
mountain system.
The Sangre de Cristo and West Elk
mountain ranges form part of the
Rocky Mountain system.
Sangre de Cristo
Mountains Range
Rocky Mountain System
Volcanic Mountains
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Recall from the previous chapters
that volcanic mountains form along
plate boundaries and at hot spots.
In addition, igneous activity forms
rock deep in the crust that can be
uplifted as a result of plate motions
and isostatic adjustment.
Folded Mountains
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Mountains that are formed
primarily by folding are called
folded mountains.
Compressional stress is the major
cause of folded mountains.
Compressional stress helped to
form the Alps in Europe.
Thrust faulting is also important in
the formation of folded mountains,
which are often called fold-andthrust belts.
Folded Mountains
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Folded mountains often contain
numerous stacked thrust faults
that have displaced the folded
rocks layers many kilometers
horizontally.
Stacked thrust faults
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The Appalachian Mountains, the
northern Rocky Mountains, and the
Alps in Europe are all examples of
folded mountain ranges.
Fault-Block Mountains
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Fault block mountains; another type
of mountain formation, is the result
of movement along normal faults.
Most normal faults are small and
have displacements of only a meter
or so.
Others extend for tens of
kilometers where they may outline
the boundary of a mountain front.
Examples fault block mountains
Fault-Block Mountains
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Large scale normal faults are
associated with fault-block
mountains
Fault-block mountains form as large
blocks of crust are uplifted and
tilted along normal faults.
Examples fault block mountains
Grabens and Horsts
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Normal faulting occurs
where tensional stresses
cause the crust to be
stretched or extended.
As the crust is stretched, a
block called a graben, which
is bounded by normal faults,
drops down.
Grabens produce an
elongated valley bordered
by relatively uplifted
structures called horsts.
Grabens and Horsts
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The Basin and Range regions of
Nevada, Utah, and California is
made of elongated grabens.
Above the grabens, tilted faultblocks or horsts produce parallel
rows of fault-block mountains.
Sierra Nevada Range
Grabens and Horsts
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In the western US, other
examples of fault block mountains
include the Grand Tetons and the
Sierra Nevada Range in
California.
Sierra Nevada Range
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These steep mountain fronts
were produced over 5 to 10
million years by many episodes of
faulting.
Plateaus, domes, basins
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Mountains are not the only
landforms that result from
forces in Earth’s crust.
Up and down movements of the
crust can produce a variety of
landforms, including
plateaus
 domes
 basins.
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Plateaus
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A plateau is a landform with a
relatively high elevation and more
or less level surface.
To form a plateau, a broad area
of the crust is uplifted vertically;
raised above the adjoining
landscape.
Colorado Plateau
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Plateaus can cover very large
areas of land such as the
Colorado Plateau which stretches
over four states.
Domes
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Broad upwarping in the rock
underlying an area may deform
sedimentary layers.
When upwarping produces a
roughly circular structure, the
feature is called a dome.
Domes often have the shape of an
elongated oval.
You can think of the upwarped
layers that make up a dome as a
large fold.
Basins
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Downwarped structures that have
a roughly circular shape are
called basins.
The central United States
contains a number of basins,
including the large Michigan
Basin.
Michigan
Basin
Basins
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During mountain building, plate
motions can cause the crust to
bend downward and form a basin.
If the basin sinks below sea level,
it may form a shallow sea.
Over time, sediments such as
sand and the skeletons of ocean
creatures are laid down, forming
layers of sedimentary rock.
Michigan
Basin
Basins
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Basins may also form along the
edges of continents where thick
layers of sediment build up. The
weight of the sediment
downwarps the crust to form a
basin.
When forces in the crust uplift
the sedimentary layers, the rock
that fills the basin is exposed at
the surface.
Michigan
Basin
Basins
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Look at the map of the Michigan
Basin to the right; it resembles a
bull’s eye. The oldest rocks are
around the edges of the basin and
the youngest rocks are near the
center.
Michigan
Basin
Basins
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The plate motions that help to
form sedimentary basins can also
destroy them.
For example, when two
continental plates collide, the
ocean basin between them closes
up.
Sedimentary rock in the basin
becomes part of the landmass
formed by the collision.
Michigan
Basin