1908.] 



PHYSICAL GEOGEAPHY GREAT SLAVE LAKE. 



29 



These temperatures for Hay River, however, are not strictly rep- 

 resentative of Great Shive Lake, since this post is situated at the 

 mouth of a hirge river which heads far to the south westward, a fact 

 which probably considerably influences the climate at its mouth. 

 The temperature conditions at other points on the southern shores of 

 the lake probably do not differ materialh^ during an average 3'ear 

 from those here recorded. On the Northern and Eastern arms, 

 however, the spring and autumn temperatures are considerably lower. 

 The winters are severe and the conditions recorded at that season 

 by the thermometer are intensified by high winds which sweep oA^er 

 the surface of the lake and in the autumn keep it from freezing imtil 

 a late date. Ice forms to a considerable thickness and persists until 

 midsummer. I have no exact data regarding the time of the freezing 

 raid breaking up of the ice during a series of years, but the dates 

 given by McConnell (loc. cit.) probably represent about the average 

 time. He says: 



Ice forms 4u the bays and along the shores of Great Slave Lake between the 

 20th and the last of October, and the whole lake is nsnally fast by the middle 

 of November.^ The ice attains a thickness of from six to eight feet. In the 

 spring the disruption of the ice takes place about the 1st of July, but sometimes 

 occurs as early as the 20th of June and as late as the 10th of July. 



In the main or western part of the lake the ice breaks up earlier 

 than in the eastern part. At Foii: Rae, according to Russell, it dis- 

 appears earlier than in the main body of the lake. The following 

 table was compiled by him from the journals kept at the Hudson's 

 Bay post: 



Dates of hreaJdng up and setting of ice in the N orthern Ann at Fort Rae. 



Y ; lee broke 

 1 up. 



Ice set. 



lear. 



Ice broke 

 up. 



Ice set. 





Oct. 19 



188-3- 



June 3 

 June 23 

 June 18 





18.5S_-. _ _ 1 June 7 



1881 _ 





18.59 _ 1 May 30 





1885 





1864 _ _ .1 



Oct. 6 

 Oct. 28 



1893 - - 



Oct. 19 



1880- _ _._ 









After the disruption of the ice the floes are tossed back and forth 

 by the winds until finally they become disintegrated. In 1903 a little 

 ice still remained about the western end of the lake until July 1. and a 

 week earlier the WrigJef/, crossing from the outlet to Fort Resolution, 

 had made its way with difficulty among the drifting floes. In the 

 eastern part of the lake the ice does not entirely disappear in some 

 seasons until late in June. 



^ The center of the lake has been known to remain open until the 1st of 

 December (fide Richardson). 



