Photographic evidence suggests that a normal wave of ice was progressing down the Muldrow Glacier prior to the occurrence of the surge in 1956. The ice thickening began before 1947, with a wave motion of about 250 m per year between 1948 and 1952. Progress may have slowed after 1952 because the bulging lateral margin had not reached the McGonagall Pass by 1954. The ice opposite McGonagall Pass thickened spectacularly after 1954 and a lateral ice cliff extended at least 1.6 km beyond McGonagall Pass when the ice began its surge movement in 1956. Aerial photographs taken after the surge ended in 1957, plus photographs from the ground in the vicinity of the bend in the Muldrow before surge motion reached that area in 1956, suggest that several small tributaries were also rejuvenated just before the surge occurred. These observations point to the possibility of climatic synchronism in the Alaskan Range and the southern ranges of North America.

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