A Comparison between the Modern and Composite Pleistocene Snow-lines, Absaroka and Beartooth Mountains, Montana-wyoming, U.S.A.

• Published in: Journal of Glaciology
• Main Author: Zwick, Thomas T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1980
• Subjects: Earth-Surface Processes; Rock Creek; Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s0022143000010534; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000010534

Abstract The modern and composite Pleistocene snow-lines of the Absaroka and Beartooth Mountains, Montana-Wyoming, were established from a population of 135 north-facing cirques and cirque glaciers distributed across Boulder River, Stillwater River, Rosebud, and Rock Creeks. The 3110 m elevation of the modern snow-line was established by connecting the accumulation-area ratios of 35 existing cirque glaciers. The composite Pleistocene snow-line was established by joining the mean floor elevations of the lowest abandoned cirques. Comparison of the modern and composite Pleistocene snow-lines indicates that the composite Pleistocene snow-line was depressed, at minimum, 305 m during the Pleistocene. The 305 m depression suggests that the mean Pleistocene temperatures were, at a minimum, 1.9 deg lower than the present mean annual temperatures found in the study area. Both the modern and Pleistocene snow-lines slope towards lower elevations in the Boulder and Stillwater drainages than in the Rosebud–Rock Creek drainages. Modern precipitation rates also show greater precipitation in the Boulder–Stillwater drainages than the Rosebud–Rock Creek drainages. The parallelism of the modern and composite Pleistocene snow-lines, and present precipitation rates suggest that temperature rather than precipitation is the controlling factor causing the depression of the snow-lines. The distribution of cirque elevations indicates that snow-lines fluctuated a minimum of four times during the Pleistocene.