156 



broken ice blocks; but under ordinary conditions the river 

 behaves more normally, slowly rising and falling with 

 variation in supply. So in a glacier, under ordinary con- 

 ditions variations in supply manifest themselves in moder- 

 ate advance or recession; but when a deluge of snow and 

 ice is thrown down in its upper reaches the conditions for 

 a spectacular advance, — a glacier flood — are introduced. 

 The ice stream flows on more rapidly, its rigid outer portion 

 is cracked and broken, its surface rises, its width increases, 

 and its front is pushed forward. There is, however, a 

 striking difference in the time occupied by the two classes 

 of floods. A river flood passes from the source to the 

 mouth of the river in a few hours or a few days, and its 

 effects are over in a few hours or a few days; but the far 

 less mobile ice requires several years for the transmission 

 of a glacier flood, and its duration is months long, while 

 years are required to bring the ice surface back to its pre- 

 flood state. 



The recent advances of the nine Yakutat bay glaciers 

 just described may be arranged as follows, when it is seen 

 that the date of advance is directly related to the length 

 of the glacier, the shortest ice tongues advancing first [47]. 



Glacier. 



Length of Glacier. 



Galiano After 1895 and] 



before 1905. 

 Unnamed glacier*. 

 Haenke. 

 Atrevida. 

 Variegated . 

 Marvine. 

 Hidden. 

 Lucia. 

 Nunatak. 



2 or 3 miles (3 to 5 km.) 



3 or 4 miles (4 to 6 km.) 

 6 or 7 miles (9 to 11 km.) 



8 miles (12-8 km.) 

 10 miles (16 km.) 

 10 miles (16 km.)** 



16 or 17 miles (25 to 27 km.) 



17 or 18 miles(27 to 29 km.) 

 20 miles (32 km.) 



* Between Haenke and Hubbard glaciers. 

 ** Excluding expanded lobe on Malaspina. 



Our Alaskan glaciers within the area vigorously shaken 

 in September, 1899, [76.] which subsequently have had 

 short vigorous periods of activity, accompanied by severe 

 crevassing and advance, that interrupted a period of stag- 

 nation or slighter activity, are listed below. Some of these 

 should certainly be added to the list of nine glaciers which 

 we know to have advanced as a result of the earthquakes 

 in 1899. 



