Abstract
ABSTRACT Little is known about the presence, distribution, age, or activity of rock glaciers in the British Columbia Coast Mountains of western Canada. Reflecting debris accumulation and mass wasting under a periglacial climate, these rock glaciers describe a geomorphic response to permafrost regimes that may or may not presently exist. An inventory of rock glacier landforms in the eastern front ranges of the Coast Mountains, using high-resolution Google Earth imagery, documented 165 rock glaciers between lat. 50°10ʹ and 52°08ʹ N. The majority of these rock glaciers occur at sites positioned between 1,900 and 2,300 m above sea level, where rain shadow effects and continental air masses result in persistent dry, cold conditions. Morphology and field observation suggest that these features contain intact ice. The rock glaciers occupy predominately northwest- to northeast-facing slopes, with talus-derived rock glaciers largely restricted to north-facing slopes. Glacier-derived features outnumber talus-derived features by a ratio of 5:1. Several of the inventoried rock glaciers were located up valley from presumed Younger Dryas terminal moraines, indicating that they formed after 9390 BP. Dendrogeomorphological investigations at one rock glacier record contemporary activity that resulted in 1.3 cm/yr of frontal advance since AD 1674. This inventory is the first to document the presence of rock glaciers in the Coast Mountains and supports preliminary understandings of permafrost distribution in the southwestern Canadian Cordillera.
Highlights
The British Columbia Coast Mountains flank the Pacific coast of western Canada, rising from sea level to more than 4,000 m in the Mt
Reflecting debris accumulation and mass wasting under a periglacial climate, these rock glaciers describe a geomorphic response to permafrost regimes that may or may not presently exist
While a provisional map suggests that much of the region is currently favorable for the development and persistence of permafrost (Hasler, Geertsma, and Hoelzle 2014), it remains to be determined whether these landforms are the fossilized remains of rock glaciers active during Late Pleistocene or Holocene permafrost conditions or whether they illustrate a geomorphic response to present-day permafrost environments
Summary
The British Columbia Coast Mountains flank the Pacific coast of western Canada, rising from sea level to more than 4,000 m in the Mt. Along their windward maritime slopes, deep winter snow packs persist into the summer months, allowing for the development of high-elevation ice fields and large valley glaciers. While ice fields are absent in the front ranges and glaciers are largely restricted to shaded northeast-facing high-elevation cirques (Falconer, Henoch, and Østrem 1965; Østrem 1966; Østrem and Arnold 1970), satellite imagery shows that rock glaciers of varying size and morphology are abundant. While a provisional map suggests that much of the region is currently favorable for the development and persistence of permafrost (Hasler, Geertsma, and Hoelzle 2014), it remains to be determined whether these landforms are the fossilized remains of rock glaciers active during Late Pleistocene or Holocene permafrost conditions or whether they illustrate a geomorphic response to present-day permafrost environments
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