National Geographic : 1900 Apr
LEVEL OF LAKE NICARAGUA lake basin itself sufficient to produce a decrease in the altitude of its surface amounting to 20 feet would almost certainly have produced more or less tilting of the surface by the subsidence of some portions of the lake's perimeter more than others. It is quite inconceivable that the region should have been warped in such a manner that the lake shore at Las Lajas should be lowered 20 feet, while the Pacific coast, only 12 miles distant, was not affected, and that at the same time every part of the lake shore should also be depressed an exactly equal amount. But if the basin had been unequally depressed, some portions of the shore would be drowned, while at other points the lake bottom would be laid bare, and raised beaches left at the former shore line. Nearly the entire circuit of the lake was made by the writer, and its shores were carefully studied with the object of deter mining whether or not there existed any evidence of recent changes in level. Owing to the regularity of the winds which prevail in this region, the different portions of the lake shore present wide differences in character, but there is everywhere a nice adjustment of shore features to present conditions. At the lower end and along the northeastern side, where there is generally an offshore wind and consequently no surf, the streams have built extensive deltas out into the lake, and the surface of the deltaplains and floodplains is regulated by the fluctuations in height of streams and lake due to seasonal changes. A depression of 6 feet relatively to lake level would permanently flood these deltaplains, while an elevation of equal amount would raise them above flood level and start the streams to deepening their chan nels and building new deltas at lower levels. Along the southwestern side of the lake there is a rather heavy surf throughout the greater part of the year. Wave erosion is there fore progressing more or less rapidly, according to the character of the rocks. The width of the beach between the water margin and the base of the wave-cut cliff is everywhere perfectly adjusted to the seasonal fluctuations in level and the character of the materials in which the cliff is cut. Any recent change in the relation of lake level to shore would necessitate a readjustment of these conditions. An elevation relatively to lake level would have raised beaches above the reach of the highest flood water. A depression would drown the beach and start the waves to cutting at a higher level. Nothing of this kind was found, and it is certain that the relations of lake level to land have not suffered recent change on this side of the lake. The changes at the upper end of the lake, in the vicinity of Tipitapa River, cited by Professor Heilprin, will be discussed later.