45 years ago we regularly went nighttime skiing on our wooden XC skis. Finally it was cold enough for Columbine lake at app 9000 ft in southern Colorado to have frozen. Across the lake we skied. Suddenly, the surface began to pitch and roll. "Break stride," cried out Captain Larry. Had we not 8 of us would have gone through the ice. Later while relaxing with our intoxicants of choice, Larry told us how troops always break stride when crossing a bridge. It is this same pnemonon that leads to washboards in our dirt roads. Thank you Captain Larry.