Destructive force of water

KENNETH CHANG

Water,usually thought of as soothing,is surprisingly heavy — and surprisingly destructive. A typical bathtub holds 40 gallons or so of water. That is 330 pounds. A cubic yard of it,filling what at first glance seems a modest volume of 3 feet by 3 feet by 3 feet,weighs nearly 1,700 pounds,as much as the Smart micro car.

And when water is moving at 30 or 40 miles an hour,like the tsunami that hit Japan,the heaviness of water turns deadly. Imagine 1,700 pounds hitting you at that speed,and each cubic yard of water as another 1,700 pounds bearing down on you. The destructiveness of a tsunami is not just one runaway car,but a fleet of them. “That’s exactly the analogy to use,” said Philip N Froelich,a professor of oceanography at Florida State University. “And by the time you’re talking about a wall of water that’s 10 metres high,if that wave is two miles long into the ocean,it’s basically like a hundred tanks coming across you.”

In addition to damage a tsunami can inflict along coastlines,it can also have an effect on the earth. Oceans are very heavy,applying enormous pressure to the ocean crust. When distribution of that pressure is shifted it can induce wobbles in earth’s rotation. It also takes a lot of force just to keep water in place. Over three million cubic yards of concrete hold back the water behind the US Hoover Dam.