Water, usually thought of as soothing and caressing, is surprisingly heavy.
A typical bathtub holds about 40 gallons of water. That's 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, according to a report in The New York Times.
And when water is moving at 30 or 40 miles an hour, like the tsunami that hit northern Japan on Friday, 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," Philip N. Froelich, a professor of oceanography at Florida State University, told the newspaper. "And by the time you're talking about a wall of water that's 10 meters high, if that wave is two miles long into the ocean, it's basically like a hundred tanks coming across you. Even though it's a fluid, it operates like a solid hammer."