Ch. 14] RECOGNITION AND PREDICTION OF PERMAFROST 263 



Recognition, Prediction, and Instrumentation 



Recognition and prediction of permafrost go hand in hand in a 

 permafrost survey. If natural exposures of permafrost are not avail- 

 able along cut banks of rivers, lakes, or oceans, it is necessary to dig 

 test pits or drill holes in places to obtain undisturbed samples for 

 laboratory tests and to determine the character of the permafrost. 



Surface features can be used with considerable degree of accuracy 

 to predict permafrost conditions if the origin of the surface forms are 

 clearly understood. Vegetation alone is not the solution, but it can be 

 used with other factors to provide data on surficial materials, surface 

 water, character and distribution of the permafrost, and particularly 

 on the depth of the active layer (Denny and Raup, unpublished manu- 

 script; Stone, 1948; Muller, 1945; Taber, 1943a). Cave-in or thermo- 

 karst lakes (thaw sinks, Hopkins, 1949; Black and Barksdale, 1949; 

 Wallace, 1948; Muller, 1945) and ground-ice mounds (Sharp, 1942a) 

 are particularly good indicators of fine-grained materials containing 

 much ground ice. Polygonal ground can be used with remarkable ac- 

 curacy also if the type of polygonal ground and its origin are clearly 

 known. Numerous types of strukturboden, polygonal ground, and re- 

 lated forms have been described and their origins discussed (Richmond, 

 1949; Cailleux, 1948; Washburn, 1947; Troll, 1945; Sharp, 1942b; 

 Hogbom, 1914) . The type of ice-wedge polygon described by Leffing- 

 well (1919) can be delimited from others on the basis of surface ex- 

 pression. The author's own work in northern Alaska (1945-1948) 

 revealed that the polygons go through a cycle that can be described as 

 youth, maturity, and old age — from flat surface with cracks to low- 

 centered polygons and, finally, to high-centered polygons. Size and 

 shape of polygons, widths and depths of troughs or cracks, presence or 

 absence of ridges adjacent to the troughs, type of vegetation, and 

 other factors all provide a clue to the size-grade of surficial materials 

 and the amount of ice in the ground. Frost mounds, frost blisters, 

 icings, gullies, and many other surficial features can be used with 

 reliability if all factors are considered and are carefully weighed by 

 the experienced observer. Geophysical methods of locating permafrost 

 have given some promise (Sumgin and Petrovsky, 1947; Enenstein, 

 1947; Swartz and Shepard, 1946; Muller, 1945; Joestings, 1941). Vari- 

 ous temperature-measuring and -recording devices are employed. Au- 

 gers and other mechanical means of getting at the permafrost are used 

 (Muller, 1945). 



