54 



GEOMORPHOLOGY: 



process extends the land out to the seaward margin 

 of the bar. While these lagoon activities are taking 

 place, the sea on the other side of the bar is constantly 

 excavating its bottom near the bar, producing an 

 ever-increasing ocean floor slope. 



Maturify. When geomorphic processes completely 

 fill in the lagoon, a new straight shoreline and deep 

 underwater shore profile result. The underwater 

 shore starts with an abrupt slope, but continues with 

 an ever-decreasing one until the shore slope merges 

 into the continental slope. This is the final condition 

 of shore stability. Unless shore features change, the 

 shoreline will not change. Such a stable shoreline is 

 said to be mature rather than old. 



SHORELINE OF SUBMERGENCE 



Shorelines of submergence are of two types, ria and 

 fiord. Ria shorelines develop from partial submer- 

 gence of land that is interlaced with rivers. As a con- 

 sequence, there is a network of bays within an other- 

 wise plain or mountain area. Fiord shorelines are 

 partly to completely submerged glacial troughs. The 

 life histories of the two types of shorelines of sub- 

 mergence are so similar that they need not be treated 

 separately (Figure 4.17). 



Initial Stage. Submergence causes an irregular 

 shoreline that reflects past elevations and depressions. 

 Such shorelines may include drowned valleys (bays 



Figure 4.17 Development along a shoreline of submergence. 



i 



