Evidence for Headwall Weathering Zones, Boundary Glacier, Canadian Rocky Mountains

Abstract

AbstractTemperature records from severalrandkluftsites at the margins and headwall of Boundary Glacier (lat. 52° 12′ N., long. 117° 12′ W.) in the Canadian Rocky Mountains are presented. These records indicate that during the ablation season a diurnal freeze-thaw air and rock-surface temperature regime occurs in a 2 m wide zone centred on therandkluftlip. Deeper in therandkluft, stable sub-zero conditions prevail whereas above therandkluftan above-freezing temperature regime prevails. The freeze-thaw temperature regime, observed freezing of melt water and rain water onrandkluftrock surfaces, and copiousin-situloose weathering products on the headwall and marginal free faces suggest an active frost-shattering environment. Down-slope migration of therandkluftlip during the ablation season results in a migration of the freeze-thaw zone and thus a seasonal extension of the rock surface area exposed to the favorable weathering environment. Longer-term glacier fluctuations, with attendant thinning and thickening of the ice body, could result in large areas of marginal and headwall rock surfaces being exposed to therandkluftweathering environment over long periods of time. The data and observations from Boundary Glacier support an idea, suggested by Battle (1960), that open and shallowrandklufts, rather than closed and deep bergschrunds, are a focus of weathering at glacier margins and thus a potential factor in cirque development.