The Neoglacial History of Robson Glacier, British Columbia, Canada

LUCKMAN, B.H.; MASIOKAS, M.H.; ARUANI, A.C.

Berna

Congreso; XVIII INQUA-Congress Quaternary sciences – the view from the mountains; 2011

INQUA

Glacier recession in the Canadian Rockies continues to reveal evidence of Holocene glacier advances prior to the Little Ice Age (LIA) maximum. Robson Glacier is unique in the Canadian Rockies with evidence of in-situ stumps overridden by three distinct glacier advances. Calendar (tree-ring dated) stumps and detrital wood with kill dates of between 1150 and 1350 A.D. represent the initial phase of the LIA at this site. Two buried forest sites were exposed close to the 1993-2000 position of the glacier snout yielding 14C-dated wood between 3300 and 3700 14C yr BP. Subsequently, wood from these two sites has been crossdated into a single chronology over 450 years. An in situ Pinus albicaulis snag ablated out of the glacier about 3km upglacier, near Extinguisher Tower at ca 2050m. Most recently wood was exposed in stream sections below a bedrock cliff, 150m below and half a km down ice of the Extinguisher site. This site contains a paleosol and logs >70cm diameter with >350 rings yielding a 14C date of 4780 +/-60 from the outermost rings. Eight of these trees crossdated to give a chronology of 560 years. The overlying till marks the earliest Neoglacial advance with in-situ material yet reported from the Rockies. The latter two events are older than Neoglacial events previously reported from sites in the Rockies at ca 2800-3000 yr BP (Peyto Advance) and 1500-1900 yr BP.