Von Hemmert, age 10, Grover, Wyo., for his question:

How does water get into a desert oasis?

Some rain falls, even in the driest of deserts. A desert occurs when the water that evaporates from the surface is more than the rainfall. A land becomes desert when the rainfall is less than five inches during an average year. But when rain does fall in the desert, it usually comes down in a deluge.

Water gushes down all the slopes and fills up the gullies. The runoff is fast. Even so, much, if not most, of the water sinks into the thirsty ground. Down it sinks to become ground water, often far below the surface. In certain places, however, the level of the ground water reaches up very near to the surface. Here plants can reach down their roots and feed upon it. There may also be a spring. If not, a well can be dug down to store ground water. This area is an oasis. The water comes from countless showers that have seeped into the earth and been stored.