A glacier is a river or great moving sheet of ice. Rivers of ice are always in valleys. They are often called valley glaciers. Great moving sheets of ice are often called icecaps.
A glacier begins as a snowfield. Little by little the snow becomes solid ice. The ice grows thicker and begins to move. The snowfield has become a glacier.
A valley glacier moves down its valley. It may move less than a foot a day. It may move more than a hundred. All valley glaciers move, but some of them do not seem to be doing so. A glacier looks as if it were standing still if the ice at the end melts as fast as more ice is pushed down. An icecap moves outward in all directions. But it may move quite a bit faster at some places than at others.
As glaciers move, great cracks appear in them. These cracks are called crevasses. Crevasses make the exploring of glaciers exciting and dangerous.
Glaciers scratch the rocks they move over. They grind up rocks, too. As a rule a glacier pushes along great piles of rock rubbish. These piles are called moraines.
Valley glaciers are common in the Alps and Himalayas. They are common, too, in Norway, Alaska, and western Canada. Glacier National Park, which has several glaciers, is in northwestern United States. Antarctica and Greenland are almost com
pletely covered with big sheets of ice.
The climate of the world has changed many times. Suppose it should get so warm that all the glaciers melted. Then the water in the oceans would rise 100 feet. A great deal of what is now dry land would then be under the sea.
This lake is left over from a much bigger one—Lake Bonneville. Lake Bonneville once covered most of what is now the state of Utah. It was a great fresh-water lake 1,000 feet deep. Water poured into it down the slopes of surrounding mountains. Through a gap in the mountains overflow water found a way to the sea.
But in time the climate of the region became much drier. Less water ran into the lake, and much that did evaporated. Finally the lake was losing more water each year than it got. Of course, the lake became shallower and smaller. At last no water ran out of it to the sea. The lake grew salty, for the water as it evaporated left behind the salt it had gathered up from rocks on its way to the lake. Now the water is much saltier than sea water. The only living things in Great Salt Lake are brine shrimps and tiny algae. Swimming in such salty water is a strange experience. The water holds a swimmer up much more than fresh water does. If he floats, a third of his body is out of water. Diving is rather dangerous. A diver may be stunned when he hits the heavy water.
Along the northwest shore of the lake are the Bonneville Salt Flats. "Flats" is a good name for them, for they are probably flatter than any other natural surface on the earth. The ground is almost pure salt. On the Flats there is an automobile racecourse. A racing car has traveled nearly 400 miles an hour on it.
Salt Lake City is near Great Salt Lake. Some of the people of the city earn their living by mining salt. Lake Bonneville left behind enough salt to last the whole world for a thousand years.
The best way to get a good view of the lake is to fly over it. On a sunshiny day the very blue lake with its border of salt makes a picture it is not easy to forget.
Physiology is the study of how living structures work. For example, in order to keep alive, all living things get ENERGY from food. They grow and reproduce new living forms just like themselves. They react to the world around them, and try to adjust to changes. As plant and animal life becomes larger and more complicated, the different parts of a body must be coordinated so they work together. Physiology studies these processes.
Because the scientist must first understand how a thing is made, before he can understand how it works, a physiologist studies the various parts of the living structure—its ANATOMY. He studies the functioning of the structure. He may study how an individual NERVE CELL sends an impulse, how the muscles of the body move together, or why a plant produces flowers at certain times of the year. But to have an understanding of the building materials of living things and the natural laws governing them, a physiologist must also know the basic PHYSICS and CHEMISTRY of the non-living world, as well as the biophysics and biochemistry of living structures.
For example a boy or girl eats food and grows bigger. The physiologist checks digestion, circulation, elimination, metabolism, respiration, and excretion to find out what is happening to the food inside the person's body.