Lake

a body of water surrounded by land. Lakes are classified, according to the kind of water they contain, into freshwater, salt, alkaline, brackish, etc. Salt lakes are of two kinds. Some were formerly fresh and have become salt because they have no outlet. As the water evaporates, it leaves behind salt and other minerals absorbed from the soil. Great Salt Lake and the Dead Sea are of this nature. Other salt lakes are simply portions of the ocean imprisoned by the sinking of the basin in which they lie, or by the rising of a ridge cutting them off from the ocean. The Aral and the Caspian Seas were once a part of the Mediterranean. Fresh-water lakes are formed in various ways. The lakes of Switzerland lie in glacial valleys. Glacial deposits hold the water back just as a dam creates a pond. The waters of Lake Pepin, a widening of the Mississippi River, are held back by a ridge of silt brought in from Wisconsin by the Chippewa.

Many lakes occupy hollows scooped out by former glaciers. The Great Lakes of North America are examples of this sort. Crater Lake, in the Cascades of Oregon, occupies the crater of an extinct volcano. Its surface is 8,000 feet above sea level. It is ten miles in circumference. It is the deepest body of fresh water in America. An underlying stratum of rock salt or other soluble mineral is sometimes dissolved by water and carried away, causing the surface to fall in, thus creating a sink lake. Such lakes are not infrequent in limestone countries.

A river has a tendency to wear away the outer shore of a bend. In alluvial soil, therefore, the channel is likely to become a series of wide bends or loops. When a loop becomes pronounced, the current has a tendency to cut across the neck, thus straightening its course. The loop thus abandoned may be filled, in part, with silt, and be converted into a crooked or ox-bow lake. There are many such in the lower valley of the Mississippi. Most of the lakes of northern North America lie in low places caused by the uneven distribution of glacial drift. This is the case with nearly all prairie lakes.

Nature is busy at work filling up and destroying her lakes. The growth and accumulation of vegetable matter and the dust blown in by the winds are rapidly converting shallow lakes into marshes and marshes into meadows. Tributaries bring in quantities of silt. The Rhone has filled in the upper part of Lake Geneva in this way. The delta has advanced into the lake two miles within historical times. The outlet of a lake has a tendency also to cut away its barrier, thus lowering its surface. So pronounced is the effect of tributaries and outlets, that geographers say "streams are the mortal enemies of lakes."

The following are the larger lakes of the world. The area is expressed in square miles. The elevation is the altitude of the surface in feet above sea level. The minus sign indicates that the surface is below sea level. The depth is also expressed in feet.