HOLOCENE GLACIAL HISTORY NEAR WHISTLER, SOUTHERN COAST MOUNTAINS, BRITISH COLUMBIA

In a multiproxy effort to reconstruct the Holocene glacial history of the Green Lake watershed in the southern Coast Mountains, 80 km north of Vancouver, British Columbia, a combination of terrestrial (dendrochronology, lichenometry, radiocarbon) and lacustrine (varve counting, tephrochronological, radiocarbon) dating methods were used. Detrital wood in the forefield of Overlord Glacier yielded radiocarbon ages between 5900 and 6200 ¹⁴C yr BP. The narrow age range suggests that the trees were killed by advancing ice ca. 6000 ¹⁴C yr BP. At Decker Glacier, just north of the watershed, in situ stumps, apparently sheared by glacier ice, and one detrital log, all on a cliff high above the present surface of the glacier, yielded ages of 2900 to 3200 ¹⁴C yr BP. The implication is that the glacier was advancing and more extensive than today ca. 3000 ¹⁴C yr BP. Moraines at Overlord Glacier were dated by dendrochronology and lichenometry to around AD 1735, 1835, 1890, and 1920 (all dates include age-height and ecesis corrections). The outermost moraine at Overlord Glacier is older than 500 years and thus indicates either an early Little Ice Age or even earlier advance. In neighbouring watersheds, glaciers yield similar results, thus indicating synchronous Little Ice Age advances and at least two separate but significant glacier advances earlier during the Holocene. The continuous record of lake sedimentation from the Green Lake watershed reveals a general increase in the clastic component of lake sediments from the early Holocene to present. One of the largest increases in clastic sedimentation occurred immediately prior to the deposition of Mazama ash (6800 ¹⁴C yr BP). Green Lake sediments are rhythmically laminated after 3200 cal yr BP. Varves are thickest at ca. 750-500 BC, AD1530, AD1740, AD1850, and between AD1920 and 1945. The last period of thick varves corresponds to a time of rapid ice retreat. We interpret earlier periods of thick varves as times of enhanced sedimentation following moraine-building events. The combined record shows good accordance in the later part of the Holocene and confirms at least two Neoglacial phases coinciding with the ‘Tiedeman’ advance and the Little Ice Age.