278 R. S. TARR RECENT ADVANCE OF GLACIERS IN ALASKA 



u]) the mountain valley well down toward the terminus of the glacier, and, 

 in the case of Marvine glacier, to the very end. 



In both Variegated and Atrevida glaciers the ice has been broken for 

 a distance of from 5 to 7 miles ; in Marvine glacier the breaking extends 

 fully 15 or 20 miles. The crevassing in all cases extends completely across 

 tlie valley portion of the glacier and down into the stagnant or nearly stag- 

 nant moraine-covered margin. In all cases the thrust is accompanied by 

 a distinct forward movement at the terminus, and in at least three 

 cases — the Variegated, Haenke, and Atrevida glaciers — there has been a 

 distinct thickening of the ice as a result of the forward thrust. It is 

 probable that there has also been a thickening in Marvine glacier,, but 

 since we did not visit it in 1905, we have no comparative observations on 

 which to base a definite statement. 



The remarkable advance of these glaciers is recent, and, in the case of 

 four of them, has mainly, if not entirely, occurred in the ten months 

 preceding June, 1906. Not only is the movement recent, but it was 

 actively in progress at the time of our visit in tlie summer of 1906. In 

 at least one case, that of Galiano glacier, a forward movement has oc- 

 curred and died out during the interval between 1890 and 1905. There 

 are indications that an advance is beginning in some of the glaciers, nota- 

 bly the Lucia and the Seward, but there are others which show neither 

 signs of the coming of such an advance nor of its having already come 

 and gone. 



From these facts it appears that, for some reason, there is a striking 

 and rapid change in progress in the glaciers of the. Yakuiat Bay region, 

 interrupting a period of long quiet and affecting different glaciers at 

 different times. One glacier has passed through the cycle of change; 

 others entered on it in 1906; still others show signs of the beginning of 

 such a cycle; but in other cases there are no indications of its approach. 



Consideration of Hypotheses 

 the problem to be solved 



Such a remarkable change in the condition of glaciers as to transform 

 an unbroken, moraine-covered valley glacier to a sea of crevasses in the 

 short interval of ten months — a phenomenon, so far as I know, not hith- 

 erto recorded — calls for a special explanation. The phenomena in the 

 field clearly prove that there has been a wave of advance passing through 

 the glaciers with such rapidity as to break the ice, instead of causing a 

 slow forward movement, such as commonly results from normal climatic 



