Linda Carpenter, age 11, of Allentown, Penna.., for her questions

What causes a desert oasis?

The driest desert receives on the average about five inches of rainfall. Sometimes ten inches fall in a few days and then not a drop for several years to come. In any case, desert rainfall is usually a rather short deluge. Some of this water runs down well worn paths perhaps to join~a distant river. Most of it sinks down into the dry sandy soil.

The ground water sinks and sinks until it comes to a bed of rock solid enough to act as a floor. Here it rests, saturating the soil often to a deep level. In a few places, however, the ground water rests near the surface. It may even burst forth in a desert spring or, with a little digging, it will ooze up to fill a pool or a well. Desert oases occur where the ground water is near enough to the surface to form a spring or a well.