Barbara Juanis, age 10, of Spokane, Wash., for her question:
HOW DID THE GREAT SALT LAKE GET SO SALTY?
This summer lots of lucky tourists will get a chance to drive across our scenic continent. Some of the luckiest ones will pay a visit to Utah's amazing Great Salt Lake. Its beauty takes your breath away and its bright shiny water is five times saltier than the seas.
When the world was young, its great oceans were filled with almost fresh water. Thousands of years ago, when the Ice Age glaciers began to melt, Utah's Great Salt Lake was filled to overflowing with almost fresh water. But through the long ages, countless tons of salty chemicals were dumped into the seas. And in the past few thousand years, even stronger concentrations were added to the dwindling lake.
This sort of thing happens as streaming rivers flow over the land, dissolving all sorts of chemicals from the rocks. Actually, their so called fresh waters carry along tiny traces of salty chemicals. Finally they empty these chemicals into the seas and lakes. Meantime, the beaming sun evaporates moisture from the surface ¬but the chemicals are left behind. This is why the seas are getting saltier all the time.
Most lakes have streams that drain away their slightly salty water as more is added by other streams. But the water in the Great Salt Lake is trapped there, just as it is in the oceans. Streams add more slightly salty water. The sun steals moisture from the surface and the chemicals are left behind and the salty lake gets saltier.
Picture a large flat basin surrounded by ranges of our Western mountains. During the Ice Age, there were glaciers in the mountain canyons. At last the ice melted and streams ran down to fill the basin with a huge lake of so called fresh water. This was old Lake Bonneville, 10 times bigger than Great Salt Lake and 1,000 feet higher.
For a time, there were streams to drain it and its water stayed fresh. Then the climate grew warmer and desert dry. As the sun stole its moisture the level sank, and it had no outlet to the sea. So the old lake shrank and its waters became even saltier than the seas.
As old Lake Bonneville shrank and sank, its beaches were left high and dry around the shores. These beaches are still there to tell the story. So are the high and dry deltas that formed where long gone streams once emptied their almost fresh water into the large old lake. Meantime, the saltwater lake lingers on at the bottom of the desert basin.