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Paraglacial processes, climate change and sediment supply |
Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6
* Corresponding author (e-mail: jclague{at}sfu.ca)
Mountain rivers, like alpine glaciers, are sensitive indicators of climate change. Some rivers may provide a more complete record of Holocene climate change than the glaciers in their headwaters. We illustrate these points by examining the record preserved in the upper part of the alluvial fill in the Nostetuko River valley in the southern Coast Mountains, British Columbia (Canada). Glacier advances in the upper part of the watershed triggered valley-wide aggradation and complex changes in river planform. Periods when glaciers were restricted in extent coincide with periods of incision of the valley fill and floodplain stability. As many as 10 overbank aggradation units are separated by peat layers containing tree roots and stems in growth position. Twenty-five radiocarbon ages on roots, tree stems and woody plant detritus in several of the peat layers closely delimit periods of aggradation. The oldest phase of aggradation occurred about 6500 years BP and coincides with the Garibaldi Advance documented elsewhere in the southern Coast Mountains. A second phase of aggradation, recorded by several units of clastic sediment, dates to about 2500 years BP, near the peak of the middle Neoglacial Tiedemann Advance. The third phase occurred shortly after 1400 years BP during or shortly after the First Millennium Advance, which has been recently documented in coastal British Columbia and Alaska. The most recent phase of aggradation began about 800 years BP and continued until recently. It coincides with the Little Ice Age, when glaciers in the Nostetuko River basin and elsewhere in the southern Coast Mountains attained their greatest Holocene size. Several periods of peat deposition during the Little Ice Age indicate periods of floodplain stability separated by brief intervals of floodplain aggradation that coincide with Little Ice Age glacier advances in western Canada. The results imply that the west fork of Nostetuko River is sensitive to upvalley glacier fluctuations and, indirectly, to relatively minor changes in climate.
