Info on Tsunamis
I've been having a hard time grasping the nature of last week's tsunami. From the video pictures of the advancing waves, it just didn't appear as devastating as it was. I suspected that this was because of a massive size difference between a tsunami and the common wind waves that we see at the beach every day. A difference that was more represented in the lenth of the wave than the visible height as the wave rose from the surface approaching land.

So, I did a little bit of looking:

The image most people have of a tsunami is a large, steep wave breaking on the shore. This image is hardly if ever the case. Most tsunamis appear as an advancing tide without having a developed wave face, resulting in rapid flooding of low-lying coastal areas. Sometimes, a bore can form during which an abrupt front of whitewater will rapidly advance inland much similar to the tidal bore formed at the mouth of large rivers.
http://www.tsunami.org/faq.htm#4

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Tsunamis are unlike wind-generated waves, which many of us may have observed on a local lake or at a coastal beach, in that they are characterized as shallow-water waves, with long periods and wave lengths. The wind-generated swell one sees at a California beach, for example, spawned by a storm out in the Pacific and rhythmically rolling in, one wave after another, might have a period of about 10 seconds and a wave length of 150 m. A tsunami, on the other hand, can have a wavelength in excess of 100 km and period on the order of one hour.
http://www.geophys.washington.edu/tsunami/general/physics/characteristics.html

So, to understand the nature of this beast, it seems that it's better to view it as its out-of-use name of tidal wave suggests. Its mass is not represented by its wave height, but by its enormous wave length. This mass manifests as a rapidly advancing tidal surge. The ocean essentially rises up and occupies low-lying areas.

The most telling pictures from the day of the event are the ones showing the rapidly flowing water returning to normal sea level. Massive rivers of returning saltwater, channeled into shallow ravines and other channels formed by man-made structures, formed over thousands of miles of normally dry coastal areas. To my mind, it's as if thousands of Mississippi Rivers just appeared out of nowhere in the middle of daily life, swept away victims, and then just disappeared.

Still difficult to fathom.

http://www.geophys.washington.edu/tsunami/intro.html

http://www.tsunami.org/
- served up by Nomad @ 1:44 PM