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What are standing wave patterns?
Waves in nature come in
many forms: on water, in air, in
electric fields, and through solid objects such as rock, metal, or the Earth
itself. In any of these cases, the wave
is a pulse or oscillation of energy that travels through the material in
question even though the material itself is not traveling. Sound waves can travel many miles through
the air, at very high speed, and yet the air itself is not moving, except as a
minute vibration passed along from air molecule to air molecule in a chain of
collisions.
It is helpful to think
of waves on water, as these can be seen with the human eye. Water waves are seen as series of high
points (crests) and low points (troughs) that propagate (travel) along a given
direction. When a pair of water waves
encounter each another, they interact or “interfere” with each other to produce
a combined wave form. Where the crests
combine, new crests form that are higher than either of the original wave
tops. Where the troughs combine, even
deeper troughs appear. Where a crest
combines with a trough, their respective high points and low points tend to
nullify each other, creating an intermediate height of water surface.
In waters where many waves traveling in all directions
interact, peak-like wave tops and hole-like troughs can form, all appearing to
“dance” up and down in place. In these
circumstances, the horizontal motion of the individual waves can be lost to the
eye altogether and the combined waves may appear to “stand” in place. Such waves are called “standing waves.”
In the picture to the left, two individual waves, one blue
and one violet, are shown. These could be two different ripples on a
watery surface, two different vibrations on a guitar string, or two different
sound waves in the air.
When
the two individual waves interact, or "interfere," with each other,
the actual appearance of the combined waves is a result of the peaks and troughs
of the two individual waves adding to or subtracting from each
other.
The result of adding the two above waves together is shown in the second
picture.
In
Tectonic Basin, the vibrations in the steel plate underneath the sand are
acoustic (sound) waves. These vibrations travel back and forth across the
plate, moving in all directions. When these traveling waves interact they
interfere with each other in a manner similar to water waves. The interference of acoustic waves creates
the troughs and crests of wave patterns in the sand of Tectonic Basin. Under
the right conditions, some of these waves may appear to stand still, or nearly
so.
Are sand dunes in nature formed by wave interference?
The forces that create sand dunes on Earth and
on other planets are not tectonic or acoustic in nature. Air movement carrying dust and sand
particles forms sand dunes. (For more
information, see Aeolian Landscape.)
Nevertheless, tectonic waves do move through the Earth and along its
surface, and their effects can be seen when they are exceptionally strong, as
during an earthquake.
How do faulted landscapes develop?
In “Tectonic Basin” lines form in the sand where dunes intersect
one another. These lines suggest faulted landscapes similar to what can be seen
when flying over the San Andreas Fault in Central California. Although
traveling and standing waves may be involved in an earthquake, these fault
lines form in a different way. They are the result of tectonic plate motions
and the crustal forces associated with them.
Earthquakes and the fault
zones in California are the outcome of the Pacific Plate sliding north past the
North American Plate. Plates are distinct, essentially rigid sections of the
Earth’s crust. The sliding process creates discontinuities in the landscape,
which are the lines in the fracture zones that we see
What other sculptures share similar features with "Tectonic Basin"?
Duning is presented most vividly in Aeolian Landscape, although the dunes are
wind-formed as opposed to the traveling and standing waves you observe in
Tectonic Basin. The sculpture Rift Zone offers
a view of geothermal activity that takes place predominantly around crustal
tectonic faults. But the formations in Rift Zone look very different from the
waves in Tectonic Basin.
Photo
Credit: United States Geologic Survey
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