| |
Orogeny
Orogeny (o-RAHJ-e-nee) is the
geological term for the process of
mountain building. Orogenies can have a number of causes. Mountain
chains can be composed of numerous erupting volcanoes, produced when
one tectonic plate slides underneath another and melts. As the
downgoing plate melts, its magma bubbles up, melts through the
overlying plate, and erupts to form a volcanic mountain chain. Many
mountain belts emerge when one tectonic
plate collides with another, producing a huge smashed-up zone
analogous to a crumpled bumper in a car collision. The rocks in
these mountain belts are highly deformed by the extreme compression
caused by the collision. They are typically folded into tight
zigzags or crumpled like a sliding carpet, or sliced up with huge
horizontal thrust faults.
Orogenic events build mountain chains, but other processes such
as erosion are constantly wearing them down. The higher the
mountain range, the steeper the slopes, and the faster gravity tears
down the mountains with landslides, rockfalls, debris flows, as well
as the constant eroding of sediment with normal rain and stream
flow.
Mountains are not forever. If the forces which produce their
uplift do not continue to keep up with their denudation by erosion,
they eventually wear down to nothing. Ranges like the Himalayas and
Rockies are still rising today, while ancient ranges like the
Appalachians have not been uplifted in 250 million years, and are
nearly worn down.
Each of these images is a 30 micron thick slice of rock, viewed
through polarized light. Along with the musical ideas and written
suggestions, the images should be used as a starting point for an
improvised interpretation of "orogeny." Allow your improvisation of
each image to unfold for approximately 30-120 seconds. You may
begin at any point on the circle, move either clockwise or
counterclockwise, as long as the circle is completed.
| View the
first page of the score |
 |
| Purchase this
score |
not yet
available |
|
