http://stream.publicbroadcasting.net/production/mp3/knau/local-knau-756317.mp3
Flagstaff, AZ – Earth Notes: Entropy Happens
The Moab region is famous for its natural arches, which open like windows into the geological past. About 2,000 of these quirks grace Arches National Park, the result of ancient seas and their salt deposits.
Superimposed sandstone layers slipped, buckled, and cracked; weathering widened the gaps. Frost, water, and heat kept at their work. They enlarged hairline fractures, wrenched away supportive rock, and collapsed the center of some fins, eventually freeing arches from their surroundings.
And then the tourists came. Utah placed Delicate Arch on its centennial license plates. But erosion never stops, and all arches are doomed to fall.
In 1991, visitors videotaped a boxcar-sized slab crashing from the roof of Landscape Arch, the longest span in the park. By August 5th, that time had come for Wall Arch, the park's 12th largest. This time nobody saw it happen.
The gradual disintegration of signature landmarks alarms some people. In the can-do spirit of the late 1960s and early 1970s, the National Park Service considered reinforcing Delicate Arch to make it last. But after brief discussion park officials wrote that trying to overcome or delay the forces of erosion or gravity would be folly at best.
Several citizens have proposed to rebuild Wall Arch, some by replacing it with a computer-modeled replica made from faux stone. Spokesman Paul Henderson says the park will not pursue these ideas, because collapse is the normal course of events. He offers this consolation: as old arches expire, new ones are being formed.
-Michael Engelhard