Late-Holocene fluctuations of the Bear River Glacier, northern Coast Ranges of British Columbia, Canada

Abstract

During Holocene advances of the Bear River Glacier, in northwestern British Columbia, ice pushed against a bedrock slope on the north side of Bear River Pass as it was being diverted eastward and westward along the pass. The result is a series of till sheets plastered against the rock slope and separated by wood mats. This sequence of tills provides an unusually detailed record of early-Neoglacial history and shows that Neoglacial expansion in the northern Coast Mountains began earlier than previously known. Moraines show the extent of ‘Little Ice Age’ expansion, and documents related to the long mining history of the area provide records of post-LIA recession. The oldest deposits in the area are a small lateral moraine outside of a prominent LIA moraine, and a till in the pass older than c. 3500 14C yr BP. The small moraine is undated; it may be equivalent to the latest-Pleistocene Crowfoot Advance which produced similar moraines in the southern Coast Mountains and eastern Cordillera. Wood mats in the pass show that Neoglacial advances occurred at c. 3700, 3500, 3300, and 1000 14C yr BP; each advance was slightly more extensive than the previous one. Documentary evidence indicates that the pass was still filled with ice in 1913, and diverging both eastward and westward, but glacier retreat has been rapid since then. Retreat from the pass in the mid-20th century resulted in the creation of Strohn Lake, through which meltwater from the glacier passes; a complicated lake history includes switching of discharge from eastward to westward and a series of jokuhlaups that damaged highway infrastructure to the west. A comparison of the history recorded at Bear River Pass with that recorded at the Todd Icefield 15 km to the north shows that different components of glacial history are preserved in different places, and many sites need to be examined to obtain a relatively complete regional history.