Lindsay Brooke, age 12 of Belvederes Calif, for the question:

What causes a tidal wave?

The so‑called tidal wave has nothing to do with the tides. For the tides rise and fall in an orderly manner. We can estimate their ebb and flow to the minute. What we call a tidal wave, however, overflows the bounds of the restless ocean. It attacks suddenly, as a powerful wall of water flooding over the land.

Such a destructive tidal wave may be caused by the wind. The howling gales of a hurricane pile up mountains of water before them. When this mass of water reaches the shore it tears over the land. This is a wind made tidal wave.

Other tidal waves are caused by earthquakes on the ocean floor. When an earthquake rocks the ocean floor, the waters above it are heaved and shaken. Huge waves build up, rippling outward from the shaken area. Such a tidal wave, called a tsunami, may fan out at a rate of 400 miles an hour. It retains its force for thousands of miles. Hours after the quake the tsunami may break with sudden fury upon far distant shores.