16 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



bulged or raised the formerly Level ice floor along the middle part of the river 

 into a low arch, whose crown, by May 26, stood about 5 feet above its edges 

 or pedal extremities, which were still frozen fast to the shores. In the mean- 

 time the excess water, increased by surface drainage due to thaw, unable to find 

 passage beneath the ice, formed broad overflow streams, several feet in depth, 

 coursing on the surface of the ice that formed the limbs of the arch on either 

 side between the crown and the shore. These conditions increased until the 29th, 

 when, at ±30 p. m., the ice, now visible in the middle of the river only along 

 the crown of the arch, broke or parted transversely and almost bodily moved 

 one-eighth of a mile downstream, when it was stopped by a jam; but at 6.30 it again 

 started and moved about a mile. Soon after this, with increased rise of the river, 

 a general breaking up of the ice took place, and it continued to run more or less 

 steadily until June 6, when the river cleared of it and became navigable. So far 

 as observed, the ice rarely exceeded 2J- feet in thickness, this comparative thin- 

 ness being probably due to the protecting heavy mantle of snow. Permanent ice 

 usually forms on the river by October 1<>. 



Stonej'" has described a break-up witnessed by him at Fort Cosmos, on 

 Kowak River, which was probably' in most respects similar to that on the Koyu- 

 kuk just described. In Stoney's description occurs the statement that "the ice 

 suddenly became covered with water, increasing in depth on both sides of the river 

 and decreasing toward the middle." As no reason appears to be assigned for the 

 otherwise peculiar increase of water at the sides and its decrease toward the middle, 

 the writer infers that this phenomenon was due to the ice-arch feature, which 

 seems not to have been recognized by the observer at the time. 



The arching feature of the ice, which seems to be characteristic in the breaking 

 up of Arctic rivers and does not attend those in temperate zones — granting a rise 

 in the water at the head of the rivers in both zones — is ascribed by the writer 

 primarily to the presence of permanent subterranean frost, in whose icy grasp 

 the edges and lateral portions of the ice become so firmly welded and held to the 

 frozen earth along shore and the shallow riparian portions of the river bed that 

 it is not released until thawed from the surface downward b}' almost midsummer 

 suns. In temperate climates, on the contrary, where perennial underground frost 

 does not exist, the longshore ice is the first to give way, and is often replaced 

 by open-water leeways due to the warming and thawing influence of the under- 

 ground temperature soon after the climax of winter is past. 



After the break-up the party proceeded by river steamboat 80 miles up the Ko} 7 u- 

 kuk to Bettles, a new supply post near the sixty-seventh parallel. From this point, 

 commencing June 13, after doing a day's work on Lookout Mountain, the work 

 was continued northward 125 miles, with Peterborough canoes, up a large tributary 



aStoney, Lieut. George M., Naval Explorations in Alaska, U. S. Naval Institute, Annapolis, Md., 1900, p. 52. 



