Unexploded shell shuts Sylvan Pass
Sylvan Pass in Yellowstone National Park was closed Monday after a construction worker found an unexploded 55-pound shell used to control avalanches. Park officials called in a team from Malmstrom Air Force Base in Great Falls to remove and detonate the shell. The road reopened midmorning Tuesday.
The incident began over the noon hour Monday when an employee of a company working on the road found the shell just east of Sylvan Pass, according to Al Nash, a Yellowstone spokesman.
Park officials believe the shell was shot sometime last year from the 105 mm howitzer that has been used for years to help control avalanches on the pass. Crews try to keep track of unexploded shells, but locating and recovering them can be difficult. "We are vigilant, but it is something of a concern," Nash said.
There may be as many as 300 unexploded shells in the hills around Sylvan Pass, according to park rangers. A 1990 National Research Council report estimated that 10 percent of dud explosives could detonate "spontaneously, without any obvious trigger."
Monday's incident is the latest in an ongoing discussion of how to deal with avalanches on the pass and protect the safety of employees and visitors.
For years, Yellowstone has relied on the howitzer, but the practice is dangerous. Park workers have to travel through an avalanche-prone area to reach the gun before shooting it into the hills in the hopes of triggering a controlled avalanche.
The shells that don't immediately explode also pose a danger for park employees and visitors.
Two years ago, the park began a pilot program in which a private helicopter is used to hand-drop explosives on the pass. The practice is safer, according to park officials, but there are times when weather conditions prevent the helicopter from flying.
Nash said the howitzer was used at least twice last year and apparently shot at least one dud.
The helicopter program is expected to continue next winter.
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