268 black. PERMAFROST [Ch. 14 



around the casing and create a settling hazard in the foundation of 

 the rig and also a disposal problem. In some foundations refrigerat- 

 ing equipment must be used to prevent settling. 



Permafrost also may act as a trap for oil or even have oil reser- 

 voirs within it. The cold temperature adversely affects asphalt-base 

 types particularly and cuts down yields. Production difficulties and 

 costs go up (Fagin, 1947). 



Refrigeration and Storage 



Natural cold-storage excavations are used widely in areas of perma- 

 frost. They are most satisfactory in continuous or discontinuous 

 zones. Permafrost should not be above 30° F. ; if it is, extreme care 

 in ventilation and insulation must be used. Properly constructed and 

 ventilated storerooms will keep meat and other products frozen for 

 years. Detailed plans and characteristics required for different cold- 

 storage rooms are described by Chekotillo (1946). 



Trafficability 



In the Arctic and sub-Arctic most travel overland is done in winter, 

 as muskegs, swamps, and hummocky tundra make summer travel ex- 

 ceedingly difficult (Navy Department, 1948-49; Fagin, 1947). 

 Tracked vehicles or sleds are the only practical types. Wheeled 

 vehicles are unsatisfactory, as most of the area is without roads. 



Permafrost aids travel when it is within a few inches of the sur- 

 face. It permits travel of D8 caterpillar tractors and heavier equip- 

 ment directly on the permafrost. Sleds, weighing many tons, can 

 be pulled over the permafrost with ease after the vegetal mat has 

 been removed by an angle-bulldozer. Polygonal ground, frost blisters, 

 pingos, and small, deeply incised thaw streams (commonly called 

 "beaded" streams), rivers, and lakes create natural hazards to travel. 



In areas of discontinuous and sporadic permafrost, seasonal thaw is 

 commonly 6 to 10 feet deep, and overland travel in summer can be 

 accomplished in many places only with amphibious vehicles such as 

 the weasel or LVT. Foot travel and horse travel are very slow and 

 laborious in many places because of swampy land surfaces and neces- 

 sity for making numerous detours around sloughs, rivers, and lakes. 



Military Operations 



Permafrost alters military operations through its effects on con- 

 struction of airbases, roads, railroads, revetments, buildings, and other 

 engineering projects; through its effects on trafficability, water supply, 

 sewage disposal, excavations, underground storage, camouflage, ex- 



