Carol Marongoni, age 14, of Long Island City, New York, for her question:

How does a tsunami differ from a tidal wave?

Tsunami is borrowed from a Japanese word meaning "storm wave." Every now and then, the people who live on shores and islands of the northwest Pacific Ocean experience unexpected floods sweeping in from the sea. These waves are unrelated to the normal daily tides that wash up and down on the beaches at schedule times. Hence they deserve a special name of their own. At scheduled times of the month or year, certain extra high tides tend to sweep over the land far beyond their usual limits. These fellows are classified as true tidal waves.

A tsunami has nothing to do with the moon caused ocean tides, even the extra high tidal waves of certain seasons. It is caused by some devastating upheaval in the floor of the ocean, often thousands of miles from land. The cause may be a shud¬dering undersea earthquake or the violent eruption of a volcano on the seabed, per¬haps more than three miles below the waves. This underwater upset displaces great masses of ocean water and sends it heaving and rocking outward in all directions. When it reaches a shore, the mighty mass of heaving water rushes inland as a flooding tsunami.