Floodplain Lakes 67 



Lakes resulting from Erosion — Although erosion tends 

 generally to destroy lakes by eliminating their basins, 

 here and there it tends to foster other lakes by making 

 basins for them. Such lakes, however, are shallow and 

 fluctuating. They are of two very different sorts, 

 floodplain lakes and solution lakes. 



Floodplain Lakes and Ponds — Basins are formed in 

 the floodplains of rivers by the deposition of barriers 

 of eroded silt, in three different ways. 



1 . By the deposition across the channel of some large 

 stream of the detritus from a heavily silt-laden tributary 

 stream. This blocks the larger stream as with a partial 

 dam, creating a lake that is obviously but a dilatation 

 of the larger stream. Such is Lake Pepin in the 

 Mississippi River, created by the barrier that is de- 

 posited by the Chippewa River at its raouth. 



2. By the partial filling up of the abandoned chan- 

 nels of rivers where they meander through broad 

 alluvial bottom-lands. Phelps Lake partly shown in 

 the figure on page 50 is an example of a lake so formed; 

 and all the other lakes of that figure are partly occluded 

 by similar deposits of river silt. Horseshoe bends are 

 common in slow streams, and frequently a river will cut 

 across a bend, shortening its course and opening a 

 new channel ; the filling up with silt of the ends of the 

 abandoned channel results in the formation of an ''ox- 

 bow" lake; such lakes are common along the lower 

 course of the Mississippi, as one may see by consult- 

 ing any good atlas. 



3. By the deposition in times of high floods of the 

 biilk of its load of detritus at the very end of its course, 

 where it spreads out in the form of a delta. Thus a 

 barrier is often formed on one or both sides, encircling a 

 broad shallow basin. Such is Lake Pontchartrain at 

 the left of the ever extending delta of the Mississippi. 



