Possible Tertiary Age for Some Antarctic Cirques

Abstract

SOME large cirques cut into the ridges above the Wright Valley, in the McMurdo Oasis, Antarctica (77° 30′ S, 161° E), are now free of ice and are below the permanent snow line (Figs. 1 and 2). Present day precipitation is approximately 100 mm of snow per year; hence it is a desert region into which the Wright Upper Glacier can only intrude 8 km before ablation losses exceed the supply of ice from the polar plateau. The cirques must have been cut during a local glaciation, not a continental one, because, during a rise of the ice of the polar plateau and a spreading of the ice sheet, precipitation in the area would be reduced even below that of the present, and even at times of lower level of the polar plateau there is little likelihood of significantly higher precipitation than at present. The latter conclusion is supported by evidence from the Taylor Valley, 20 km south of the Wright Valley, where that much of the valley has been ice free for at least 2.7 m.y.¹.