LONG TERM SEDIMENT YIELD DYNAMICS IN A GLACIATED ALPINE WATERSHED- CLIMATE AND GEOMORPHIC INTERACTIONS REVEALED BY LACUSTRINE VARVES

Sediment yield variations represent a key means of understanding fluvial processes and the influence of external climate and watershed processes. Few long records exist to evaluate variations in sediment yield, particularly in glacierized systems where changes in glacier extent and sediment production can be substantial. This study investigated long term sediment yield dynamics through the use of a 700-year varve record from Summit Lake, located in White Pass on the British Columbia-Alaska border. The record indicates sediment yields declined from AD 1300-1400, followed by a prolonged period of above average yield until AD 1750. Sedimentation sharply declined after AD 1848 and has been below average since. These phases of yield appear to correspond to increased yield during glacier growth in the headwater cirque, followed by reduced yield during maxima ice extent. Yield was reduced further during the post-AD 1848 period when the ice retreated. These results suggest that high yields in this terrain are supported by active glacial erosion processes and a limited paraglacial regime follows ice retreat in alpine catchments. Similarly, increased autumn rainfall-induced sediment yield post-AD 1675 appears to have occurred during a time of above mean yield inferred from glacial periods, although the increase in rainfall-induced yield occurred substantially after the increase in overall yield.