Franklin Russell Kent, age 9, of San Diego, California, for his question:
What makes springs of water happen?
When the pioneers crossed the mountains into Southern California, they found a spring beside the lazy Green River. Its crystal clear water was fresh and cool, even in the hottest weather. Some years ago, a wide freeway came stomping through and the spring dried up. Or so it seemed. Actually its water ran along underground. Later it bubbled out on the other side of a hill.
A spring cannot happen just anywhere. Things must be just right for it under the ground. There must be lots of water down there, trapped in the pores and pockets of the rocks. The solid ground is actually made of different rocks, arranged in layers somewhat like a huge crusty sandwich. Spring water comes from saturated porous rocks, where the underground layers happen to be tipped and tilted. Also there must be plenty of showers or melting snows in the neighborhood.
If all the rain water stayed on the ground for a year, we would be wading around in three feet of water. We tend to think that all the rainfall runs off in steams and rivers to join the salty seas. But this is not so. Most of it sinks down through the ground. It trickles and percolates through limestones, sandstones and other porous layers. Some of it sinks and settles three miles down. Some stays near the surface. But all of it must behave like water.
When you tip a bucket and pour in water, the runny liquid levels itself to get a flat top. The ground water also must do this. In hilly places, thick chunks of rocky sandwiches are tipped and tilted. The ground water in a layer of porous rock must sink until its top is flat and level. The porous rock may be deep below the hill top, but its slanted edges may reach the surface down the slopes. The water inside its pores and pockets trickles around. And when it reaches a weak spot of this sort near the surface, it knows just what to do. It comes gushing outside in a bubbling spring.
Most springs from gentle hills are fresh and cool. But sometimes their water dissolves calcium and other hard chemicals from the rocks underground. Other springs are changed by different underground situations. Some form in thick beds of lava, where the deep rock is still hot from fiery old volcanos. These rocks heat the ground water. Sometimes they boil it to frothy steam or mix in smokey fumes. Then it may come forth in hot springs or spurt up foamy geysers. Some warm springs puff up smokey fumaroles.
There is ground water even under our dry deserts and prairies. Here and there it comes out in an oasis spring. It may feed a grove of willows and cottonwoods. Wild flowers and mosses often thrive there in the moist, shady soil. An oasis in the hot Sahara desert is edged with palms and tropical plants and its spring water may irrigate fields of crops for miles around.