Abstract

Frank Mackie Glacier repeatedly advanced across the Bowser River valley in northwestern British Columbia to impound Tide Lake during the Holocene. The most recent infilling of Tide Lake was associated with a late Little Ice Age glacier advance and ended around 1930 when the lake catastrophically drained. Over the last century Frank Mackie Glacier has retreated and down wasted to reveal multiple glaciogenic sedimentary units within the proximal faces of prominent lateral moraines. The units are separated by buried in-situ tree stumps and laterally contiguous wood mats deposited on paleosols. Dendroglaciological and radiocarbon dating of these wood remains show that Frank Mackie Glacier expanded into standing forests at 3710–3300, 2700–2200, 1700–1290, 900–500, and 250–100 cal. years BP. These advances coincide closely in time with the previously established Tide Lake glacier dam chronology and with the Holocene history of other glaciers in the Bowser River watershed. The findings emphasize the likelihood that most glaciers within northwestern British Columbia underwent substantial size and mass balance changes over the last 4000 years, and often spent hundreds of years in advanced positions before retreating.

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