Abstract

Large earthflows in south-central British Columbia have exhibited regionally consistent fluctuations in their movement during the Holocene. Over the past 60 years, air photographs show that many earthflows were reactivated during the relatively wet period 1950–1985. Over the past 300 years, a fairly coherent relationship is established between periods of wetter climate, defined by the tree-ring record, and phases of slope movement, defined by the record of compression-wood development in conifers located near earthflow headscarps. On a time scale of several thousand years, stratigraphic evidence shows that many large earthflows in the region underwent significant reactivation of movement in the post-Mazama period, during the relatively wet, cool Neoglacial interval of the Holocene. These lines of evidence indicate that Holocene hydroclimatic changes have exerted an important influence on the regimen of large earthflows. Earthflows present a wealth of paleogeomorphic information, hitherto largely neglected, that allows a reconstruction of the changing rate of mass movement with time.

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