Calendar-dated, early 'Little Ice Age' glacier advance at Robson Glacier, British Columbia, Canada

Abstract

Dendrochronological studies at Robson and Bennington Glaciers have provided the first calendar dating of an early 'Little Ice Age' glacier advance in North America. Dates derived from in-situ stumps indicate that Robson Glacier began over-riding forest between c. AD 1142 and 1150 and continued until at least AD 1350. The highest rates of glacier advance (c. 3.8 m yr-1 ) occurred between AD 1214 and 1261 based on a series of kill dates from in-situ stumps. Between c. AD 1142-1214 and 1261-1350 rates were somewhat lower at c. 2-2.5 m yr-1. This glacier advance terminated upvalley of the 'Little Ice Age' maximum position of Robson Glacier and there is no evidence at this site for glacial events between AD 1350 and 1783. However, two smaller glaciers in the Robson area and the main tongue of Small River Glacier have outermost 'Little Ice Age' moraines that date from the first decades of the AD 1700s. All glaciers examined in the Mount Robson area have several well-developed moraines dating from the period \c. AD 1840-1900. At Small River Glacier two vegetated moraines occur 50-100 m beyond the nineteenth-century moraines. These have minimum dendrochronological ages of AD <1550 and <1600 but could be much older features. New sites at and upvalley of the present Robson Glacier snout indicate the glacier also over-rode forest areas between 3100-3300 and 3400-3700 14C years BP.