The news lately has been dominated by the tsunami that might result from the earthquake in Chile. Listening to the pretty, articulate people trying to explain what will happen has caused me to pull together some of the things I've been told about waves and about other similar phenomena including dust devils, tornadoes, and hurricanes.
Waves are described as water in motion and the idea is that the water will rush away from the source of the disturbance. Tain't so. A wave is a packet of energy.
As this energy clump moves thru the water it creates the liquid equivalent of an horizontal tornado with the water on top moving "forward;" i.e. in the same direction the energy pulse is moving, and the water below moving backward to fill the hollow left by the upper droplets. An individual water molecule caught in a wave describes a more or less circular path as seen from the side of the wave.
Note that the air molecules or dirt clods or houses caught up in a tornado do not remain with it, but ride the energy packet for a while and are then spat out into Oz (or more frequently Kansas).
Out in mid-ocean, waves, in isolation, are smooth and don't really involve large vertical movements unless you're in the "Roaring Forties" of the Southern Ocean where the wind pumps its energy into the water during a complete circumnavigation of the earth. Steep waves are found where the bottom is shoaling and the circular motion is forced upward, or where waves and currents interact and conflict with each other.
Just as coherent light waves can interact to form patterns of bright and dark bands, so interacting water waves can form huge peaks and valleys. This interaction can occur when a wave finds itself in a bay or harbor and the reflected wave off one shore collides with another wave, or in the open ocean where waves formed by one weather system meet those from another.
The Chilean earthquake was the result of a lack of lubricity. The floor of the Pacific Ocean is growing as molten lava bubbles up along the central rift and cools on meeting the water. This results in "tectonic plates" which slide away from the rift. Near the western edge of the North American and South American continents, the plates burrow down beneath the continental plates. When they slide smoothly there are no earthquakes, just a gradual change in the elevation of the shore.
Unfortunately, the materials are rough and irregular. They snag and prevent movement for varying periods of time. During this pause the pressure builds until the forces are great enough that the snag breaks and the plate snaps forward. Large changes in the level of the sea floor take place when this happens and the water above is disturbed.
When you raise water up, you endow it with "potential energy." When you lower it, you similarly endow the water around the hollow. This also holds true for solids like rock, but the difference between a solid and a liquid is that the liquid acts almost immediately to correct the imbalance. Thus the change in the elevation of the sea bed gives energy to the water and this packet of energy goes racing away from its point of origin, gradually dissipating into the atmosphere as heat.
Waves "break" when a shoaling bottom, or interference from other waters in motion, forces them into such a steep sided form that the forward rushing water on top is no longer supported from below. A following wind will also contribute to this turbulence.