JACKSON, Wyo. (AP) — Only three of more than 100 howitzer shells launched to trigger avalanches failed to explode this winter on Yellowstone National Park's Sylvan Pass.

The dud bombs are still likely imbedded in the snowpack or talus.

Yellowstone Ranger Brad Ross tells the Jackson Hole News & Guide that the duds will be found and detonated this summer.

Ross says the avalanche operations at Sylvan Pass this winter were a success.

With the winter not yet passed, he said there likely will be at least one more avalanche operation on Sylvan Pass before Yellowstone's East Gate is opened to wheeled vehicles on May 2.

Through the end of February, 114 snowmobiles and no snow coaches passed through the East Gate or used the road threatened by Sylvan Pass avalanche paths.