NEW CONSTRAINTS ON HOLOCENE GLACIATION IN GARIBALDI PROVINCIAL PARK, BRITISH COLUMBIA, CANADA

Detailed mapping of Holocene moraines near Garibaldi Lake, British Columbia, and sediment cores from adjacent lakes indicate at least three distinct periods of glacier advance since ~9000 cal yr B.P. Ice limits defined by moraines, erratics, and trim-lines that are preserved within cirques and below small modern glaciers allow us to reconstruct the extent and mass-balance gradients of glaciers during the local Holocene maximum. Assuming accumulation-area ratios of 0.65, these reconstructions indicate that equilibrium-line altitudes were as low as ~1800 m during the Holocene, roughly 200 m lower than the ELAs of the modern glaciers. Historical photos and dendrochronology suggest the Holocene maximum occurred within the past several hundred years, during the Little Ice Age; ¹⁴C analysis of wood collected from within the moraines should help constrain this.

To complement the discontinuous records from the moraines, we collected sediment cores from lakes below the moraines; these cores preserve continuous records of Holocene glacial vs. non-glacial sedimentation. Analyses of the cores include magnetic susceptibility, loss-on-ignition (organic carbon), particle sizing, tephra identification, visual and photographic logging, and AMS ¹⁴C dating of macrofossils. In addition, we plan to analyze the cores for paleomagnetic secular variation in order to develop a continuous time scale for the sediments. Preliminary results from a core of Black Tusk Lake indicate three major episodes of post-Pleistocene clastic-rich (glacial) sedimentation, suggesting an early advance at ~5900-4900 cal yr B.P., a second advance beginning at ~2570 cal yr B.P., and a third advance associated with the Little Ice Age beginning ~750 years B.P. Although glaciers appear to have been present in the Black Tusk Lake drainage throughout the latter two events, ice disappeared from this area sometime during the past century. Our Holocene glacial sequence is generally consistent with results from Kwoiek Creek drainage, ~50 km to the east (Souch, 1994).

(Souch, C., 1994, Geografiska Annaler, 76A, no. 3, p. 169-185.)