404 



EARTH FEATURES AND THEIR MEANING 



(trench) . Such a basin when occupied by water yields a lake which 

 is long, straight, deep, and narrow, and is in addition bounded on 



^___^ the sides by steep rock cliffs. At the ends the 



shores are generally by contrast decidedly low. 

 If the hard rock at the bottom of the lake 

 could be examined, it would be found to be of 

 the same type as that exposed near the top of 

 the side cliffs. The valley of the Jordan in 

 Palestine is a rift of this character and was at 

 one time occupied by a long and narrow lake 

 of which the Dead Sea and the Sea of Galilee 

 are the existing remnants (Fig. 433). 



One of the most striking examples of a rift 

 valley lake is Lake Tanganyika, while Albert 

 Nyanza, Nyassa, and 

 Rudolf in the same 

 region are similar 

 (Fig. 434). 



Earthquake lakes. 

 The complex adjust- 

 ments in level of the 

 surface of the ground 

 at the time of sensible 

 earthquakes are many 

 of them made apparent in no other way 

 than by the derangements of the surface 

 water. This is at such times impounded 

 either in pools or in broad lakes, which 

 inasmuch as they date from known earth- 

 quakes have been called " earthquake 

 lakes," even though in a strict sense any 

 lake which has originated in earth move- 

 ments might properly be regarded as an 

 earthquake lake. To avoid unnecessary 

 confusion, the term must, however, be re- 

 stricted to those lakes which are known to 

 have been formed at the time of definite earthquakes (Fig. 435). 

 Reelfoot Lake in Tennessee, which in late years has acquired 

 undesirable notoriety because of the feuds between the fishermen 



FIG. 434. Map show- 

 ing the rift-valley 

 lakes of east Central 

 Africa. 



FIG. 435. Earthquake 

 lakes which were formed 

 in the flood plain of the 

 lower Mississippi during 

 the earthquake of 1811 

 (after Humphreys). 



