著者

James R. GOFF Stephen R. HICOCK

出版者

The Association of Japanese Geographers

雑誌

Geographical review of Japan, Series B (ISSN:02896001)

巻号頁・発行日

vol.68, no.2, pp.95-106, 1995-12-31 (Released:2008-12-25)

参考文献数

26

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Quaternary sediments and landforms in a small, mountain catchment (Silverhope drainage basin) provide a link with catastrophic outburst deposits in a neighbouring valley (Chilliwack River). The contiguous catchments are linked by a pass at 1015 masl, which represents the maximum elevation of the outburst conduit. During Cordilleran Ice Sheet decay, the normal meltwater drainage pathway to the south in Silverhope valley was blocked by a dead ice dam. The area covered by the resulting glacial lake Silverhope is suggested based on elevations of a raised delta, mass movement features, and glaciolacustrine sediments. Exposures near Hicks Creek-Post Creek pass are used to infer that lake levels were raised above the elevation of the divide by a second dead ice dam. Southsouthwest oriented paleoflow deposits covering glaciolacustrine sediments northeast of the pass, and clean bedrock faces southwest of it, suggest that the dead ice dam was situated at the divide. Consequent catastrophic discharges flowed down Post Creek into Chilliwack valley. Radiocarbon ages from Chilliwack valley, and outburst sediments deposited against the distal side of the end moraine that dams Chilliwack Lake are used to infer that outburst occurred about 11.4 ka.

著者

James R. GOFF Stephen R. HICOCK

出版者

The Association of Japanese Geographers

雑誌

Geographical review of Japan, Series B (ISSN:02896001)

巻号頁・発行日

vol.68, no.2, pp.209-217, 1995-12-31 (Released:2008-12-25)

参考文献数

26

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Downstream variations in clast size were examined in Silverhope Creek, a tributary of the Fraser River, British Columbia, Canada. A sedimentary environment inherited largely from Cordilleran Ice Sheet decay dominates the present fluvial regime. Hummocky terrain in the southern part of the catchment produces distinct grainsize fluctuations over several km that are related to local changes in the sedimentary regime during deglaciation. Similarly, relict mass movement features impart grainsize variations of a glacigenic origin on the bed material. Sediment input primarily from western tributaries produces local downstream coarsening. Landslide-damming of Silver Lake about 1100 years ago provides a local base level in the northern half of the catchment. Fining associated with aggradation upstream and coarsening associated with degradation downstream also interrupt the expected trend toward downstream diminution in clast size. Geomorphic activity of anthropogenic origin is subordinate to that generated by natural processes. Sediment input shows greater bimodality in more recently-logged tributaries. Bimodality of sediment input has declined over a period of 5-10 years following the cessation of logging activity in the tributary. The main reason for a decline in bimodality is forest regrowth and valley side stabilisation. However, sedimentation rates in Silver Lake remain high indicating that the quantity of sediment input as a result of tree removal may remain high in the long term, whereas change in sediment quality (bimodality) is a short term factor.