Sentence:  The greatest variation in cover thickness, as determined from collapsed <WSD>pingos</WSD>, is in irregularly shaped <WSD>pingos</WSD>, or those with asymmetrically located ice-cores. 
Meaning of the word marked with <WSD> tags:  A conical mound of earth with an ice core caused by permafrost uplift, particularly if lasting more than a year. (from 1920s)