Physics Photo of the Week
February 22, 2013
Dendritic erosion
It's
intriguing to compare physical appearances between small
objects and much larger objects. This photo emphasizes
the brief erosion channels that appear in the sand on a beach
formed by the receding wave. The dendritic appearance of
the small beach drainage channels resembles the dendritic
appearance of rivers draining a continent on Earth. Once
a small channel becomes eroded, it channels more and more
water, with other channels joining forming the dendritic
appearance. The resulting miniature "gorges"
eventually eventually empty into the water's edge and soon
become erased by the next wave.
Compare the sand channels in the beach with Colorado plateau
erosion just
north of the Black Canyon of the Gunnison in western Colorado
in the right hand photo. The steep walled Black Canyon
traverses the lower part of the aerial photo made by myself on
a commercial flight. The canyon's rim is at the top of
the steep scarps about 1/4 from the bottom of the photo.
The broad plateau area from the scarps toward the center of
the photo slopes gently to the north, away from the Black
Canyon, toward the next valley and irrigated cropland in the
photo's center near Crawford, CO. The morphological
similarity with the beach sand erosion is striking!
The erosion channels that appear in the beach slope are
spaced about 10 cm apart. The erosion channels in this
Colorado mesa are about 700 m apart. This
self-similarity spans space by a factor of 7000. Similar
erosion channels can be seen in a map of the rivers and
tributaries on a continental scale (about 1000 times greater
than this plateau, and 10 million times the scale of the beach
sand channels). The time for the beach channels to
appear and disappear are about 10 seconds - the period between
waves. However, the time scale for the Colorado plateau
erosion channels is millions of years compared to a few
seconds for the beach sand. The time scales for these
similar formations span a factor of a factor of
billions!
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us. Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.
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