Physics Photo of the Week
October
30, 2008
Ripples Old and New
Ripples
cast in stone are not too unusual on the Earth. The ripples
pictured here are part of the Grinnell formation in Glacier National
Park, Montana. Dr. Tony Irving, University of Washington, is
pointing out
the petrified ripples. These ripples were once the fresh loose
sediment (mud, sand) in a creek, river bottom, or tidal flats from an
ocean shoreline millions of years ago. The flow of the water
tends to generate the ripples as shown by recent ripples in the sandy
bottom of the Swannanoa River in the picture below.
If the sedimentation was quick enough, the sediments rapidly built
up
to thicker and thicker layers enabling the ripple marks 
to
be
preserved. Later tectonic
(mountain building) processes
compressed and heated these sediments under several
kilometers of earth
for millions of years. Eventually the high pressure and
temperature caused a transformation: the mud and sands become fused
together to form hard sedimentary rocks. This process generates
"metamorphic" rocks - rocks that have been formed from sediments, but
fused together from the tremendous pressure and temperature to become
very hard rocks. Some of the layers were very 
highly metamorphosed into "quartzite" shown in the photo at
bottom left. In this photo, one can distinctly see the
ripple-like rocks sandwiched between the much more metamorphosed
quartzite rocks.
The pictures of the rock ripples were obtained during a Chautauqua
course sponsored by the University of Washington on the "Tectonics of
the Northern Rocky Mountains" during the summer of 2008, led by Tony
Irving.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an 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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of
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