B. Crystal Lake, a landslide lake in Colorado.
(Photograph by Howland Bancroft.)
Ox-bow lakes.—The cutting off of a meander within the flood plain of a river yields a lake which is of horseshoe (ox-bow) outline and lies generally with low banks within a plain composed of river silt. Before separating from the parent stream the meander had begun to silt up, especially at the ends. Ox-bow lakes are, however, relatively deep near the convex shore and correspondingly shallow toward the concave margin ([Fig. 451]).
Fig. 451.—Diagrams to bring out the characteristics of ox-bow lakes, together with a map of such lakes from the flood plain of the Arkansas River.
Fig. 452.—Diagrammatic section to illustrate the formation of saucer-like basins between the levees of streams flowing in a flood plain.
Saucer lakes.—As we have learned, a river meandering in its flood plain has banks which are higher than the average level of the plain, for the reason that at flood time the main current of the stream still persists in the channel, thus allowing the burden of sediment to be dropped in the relatively slack water upon its margin. Because of these natural embankments or levees, tributary streams are often compelled to flow long distances in nearly parallel direction before effecting a junction. Between the trunk stream and its tributaries, likewise bounded by levees, and between streams and the valley walls, there thus exist low basins which are more or less saucer-shaped ([Fig. 452]). At flood time, when the levees are overflowed or crevassed, water enters these depressions, and an additional supply may be derived from the walls of the valley. Good illustrations of such lakes are furnished by the flood plain of the former river Warren near the banks of the present Minnesota River ([Fig. 453]).
