Smithsonian Report. 1950.— Black 



Plate 7 



-^y^^^ 



%- 





]. Ice laccoliths (small ground-ice m( uiid, small pingo, or frost blister) produced 

 by the heaving of the active layer by the hydrostatic pressure of water 

 trapped between downward-progressing seasonal frost and permafrost in a 

 swampy lake bed, near Barrow, Alaska. Four inches of moss and other 

 vegetation covers a plano-convex disk about 15 inches thick and 5 feet in 

 diameter. Photographed October 4, 1949. 



Peat mound (fro^t mound), partially dissected t)y slumpuig along a lake about 

 25 miles southeast of Barrow, contains several bodies of clear ice underlying 

 peat. The ice was introduced in part by filling by sublimation in horizontal 

 contraction cracks and in part by forceful injection of water along a zone 

 between the active layer and permafrost. Photographed August 21, 1946. 



