1911 Encyclopædia Britannica/Hummock

HUMMOCK (of uncertain derivation; cf. hump or hillock), a boss or rounded knoll of ice rising above the general level of an ice-field, making sledge travelling in the Arctic and Antarctic region extremely difficult and unpleasant. Hummocky ice is caused by slow and unequal pressure in the main body of the packed ice, and by unequal structure and temperature at a later period.