Greg Gegenheiiner, Age 13, Of Houston, Tex., for her question:

What causes a tidal wave?

As a rule, a tidal wave is not related to the daily tides which are caused by the Moon. For this reason, geologists prefer to give it another name. It is called a Tsunami, and a tsunami may be caused by an upset on the floor of the ocean or by a distant hurricane.

Earthquakes and volcanic eruptions occur on the floor of the seas as they do on Land. When this happens, the water above the upset is heaved and shaken. Mighty waves pile up and roll along to cause a tsunami on some distant shore. Mighty waves also pile up before the winds of a hurricane, and they too may cause a tsunami.