During a recent trip I looked out the window of the plane somewhere over the southern Midwest. There was a reservoir held up by a dam.

When you look below the dam, you can see the little river meandering around the valley. There are roads, houses, industrial parks and fields in the valley. If for any reason the dam is breached, due to an earthquake, a 100-year-flood or some structural damage, the entire reservoir will thunder down the valley, destroying everything in its path.

I am sure if you live down in that valley and go shopping at the local Wal-Mart, you never give that much thought. Looking down from 39,000 feet, I got goosebumps just looking at it.