LITTLE ICE AGE FLUCTUATIONS OF GLACIERS ON MT. BAKER, WASHINGTON

Composite lateral moraines of Coleman and Easton glaciers provide evidence for an advance of glaciers on Mt. Baker, Washington, during the past millennium. An unconformity about 12 m below the crest of the southwest lateral moraine of Coleman Glacier is marked by a laterally continuous wood mat that was first identified and dated by Don Easterbrook. The wood mat dips into the proximal flank of the moraine and contains logs up to 0.4 m diameter. We obtained a radiocarbon age of 940 ± 50 ¹⁴C yr BP (AD 1000-1210) on one of the logs. The mat records a forested surface that was overridden by Coleman Glacier during an early Little Ice Age advance. Two unconformities exist in the east lateral moraine of Easton Glacier. The lower unconformity, approximately 40 m below the crest of the moraine, is marked by a mat of wood and deformed peat that gave an age of 5260 ± 70 ¹⁴C yr BP (5910-6270 cal yr BP). The upper unconformity, located 4 m below the moraine crest, contains a thin layer of wood fragments and small logs. A piece of wood from the layer returned an age of 410 ± 40 yr BP (AD1430-1630). An advance of Coleman Glacier early during the past millennium is consistent with evidence for advances of the same age in the Coast Mountains of the British Columbia and the Canadian Rocky Mountains. The advance of Easton Glacier sometime after AD 1430 appears to be broadly synchronous with mid Little Ice Age advances of glaciers in the Garibaldi Provincial Park and in the Mount Waddington area of the southern Coast Mountains, British Columbia. Taken together, the evidence suggests that Little Ice Age glacier fluctuations at Mount Baker mirrored those in the Canadian Cordillera.