Late-glacial alpine glacier advance and early Holocene tephras, northern British Columbia

Two related studies in northern British Columbia are presented. The first documents moraines in Finlay River area that record an advance of alpine glaciers. A minimum age of 9230 radiocarbon yr BP and the relation of moraines to ice-stagnation deposits suggest the advance is Younger Dryas in age. The advance demonstrates Younger Dryas glacier expansion differs in magnitude in western Canada, suggesting a complex glacier response to late-glacial climate change. The second study describes four early Holocene tephras. Two phonolitic tephras, older than 9180 radiocarbon yr BP, were found in sediments from Finlay River and Dease Lake areas. Their source may be a large volcano in northwest British Columbia. Two other tephras were recovered from Bob Quinn Lake. A lower basaltic tephra was produced by an eruption near Iskut River 8400 radiocarbon yr ago. The upper phonolitic tephra is 6000-7000 radiocarbon yr old.