PERMAFROST — BLACK 



277 



Temperature gradients from the base of permafrost up to the depth 

 of minimum temperature vary from place to place and from time to 

 time. In 1947-48 four wells in northern Alaska had gradients be- 

 tween 120 and 215 feet per degree centigrade (data of J. H. Swartz, 

 G. K. MacCarthy, and K. F. Black). 







Diagrammatic cross section through Alaska, along long. 150°, showing approximate 

 distribution of permafrost and thickness of active layer 



Diagrammatic cross section through Asia, along long. 120°, showing approximate distribution of 

 permafrost and thickness of active layer. (Modified from unpublished cross section by I.V. Poire'.) 



Active layer 



|<^^^ Discontinuous permafrost 



Continuous permafrost ^^ Sporadic permafrost 

 Figure 2. — Representative cross sections of permafrost areas in Alaska and Asia. 



The shape of a temperature curve indicates pergelation or depergela- 

 tion (aggradation or degradation of permafrost) (Muller, 1945; 

 Taber, 1943a). Some deep temperature profiles have been considered 

 by Russian workei"S to reflect climatic fluctuations in the recent geo- 

 logic past. No known comprehensive mathematical approach has 

 been attempted to interpret past climates from these profiles, although 

 it seems feasible. Some of the effects of Pleistocene climatic varia- 

 tions on geothermal gradients are discussed by Birch (1948) and 

 Ingersoll et al. (1948). 



Character. — Permafrost is defined as a temperature phenomenon, 

 and it may encompass any type of natural or artificial material, 

 whether organic or inorganic. Generally permafrost consists of va- 

 riable thicknesses of perennially frozen surficial unconsolidated ma- 

 terials, bedrock, and ice. Physical, chemical, or organic composition, 

 degree of induration, texture, structure, water content, and the like 

 range widely and are limited only by the extremes of nature or the 



