Tide-water Glaciers. 



101 



At its end there is a cliff of black, dirty ice, scarcely to be dis- 

 tinguished from rock at a little distance, from the base of which 

 flows a turbid stream. This glacier is covered so completely 

 with earth and stones that not a vestige of the ice can be seen 

 unless we actually traverse its surface. Its appearance suggests 

 the name of Black glacier, by which it is designated on the 

 accompanying map. 



The visitor to Haenke island has examples of at least two well- 

 marked types of glaciers in view : The small debris-covered ice- 

 streams, too small to reach the water, are typical of a large class 

 of glaciers in southern Alaska, wdiich are slowly wasting away 

 and have become buried beneath debris concentrated at the sur- 

 face by reason of their own melting. The Galiano glacier is a 

 good example of this class. The Hubbard and Dalton glaciers 

 are fine examples of another class of ice-streams which flow into 

 the sea and end in ice-cliflfs, and which for convenience we call 

 tide-ivater glaciers. Nowhere can finer or more beautiful ex- 

 amples of this type be found than those in view from Haenke 

 island. 



Figure 1 — Diagram illustrating the Formation of Icebergs. 



The formation of icebergs from the undermining and breaking 

 down of the ice-cliffs of the tide- water glaciers has already been 

 mentioned. But there is another method by Avhich bergs are 

 formed — a process even more remarkable than the avalanches 

 that occur when portions of the ice-cliffs topple over into the 

 sea. The ice-cliffs at the foot of the tide- water glaciers are really 

 sea-cliffs formed by the waves cutting back a terrace in the ice. 

 The submerged terrace is composed of ice, and may extend out a 

 thousand feet or more in front of the visible part of the ice-cliffs. 

 These conditions are represented in the accompanying diagram 

 (figure 1), which exhibits a longitudinal section of the lower end 

 of a tide-water glacier where it pushes out into the sea. 



As the sea-cliff of ice recedes and the submerged terrace in- 

 creases in breadth there comes a time when the buoyancy of the 



15— Nat. Geog. Mag., vol. Ill, 1.^91. 



