Late Holocene glacial activity of Bridge Glacier, British Columbia Coast Mountains

Abstract

Bridge Glacier is a prominent eastward-flowing valley glacier located on the east side of the Pacific Ranges within the southern British Columbia Coast Mountains. The terminus of Bridge Glacier has retreated at rates up to 125 m/year over the last 50 years and currently calves into proglacial Bridge Lake. Field investigations of the recently deglaciated terrain and moraines led to the discovery of detrital boles and glacially sheared stumps. Dendroglaciological analyses of this subfossil wood produced five radiocarbon-controlled floating tree-ring chronologies. The relative age and stratigraphic location of these samples revealed that Bridge Glacier experienced at least four periods of significant advance during the late Holocene: a Tiedemann-aged advance ca. 3000 14C years BP, an unattributed advance ca. 1900 14C years BP, a first millennium advance ca. 1500 14C years BP, and a Little Ice Age advance beginning ca. 700 14C years BP. Lichenometric investigations at eight terminal and lateral moraine complexes identified early Little Ice Age moraine stabilization during the late 13th to early 14th centuries, with subsequent ice-front oscillations ending in the middle 15th, early 16th, middle to late 17th, early 18th, middle to late 19th, and early 20th centuries. These investigations build upon previous research and compliment recent geobotanical evidence emerging from other glaciers in this region that describe multiple late Holocene glacier advances. The discovery of a glacially sheared whitebark pine stump dating to 1500 ± 50 14C years BP provides irrevocable proof for an advance of Bridge Glacier during a time when glaciers throughout Pacific North America were also expanding.