Early Holocene glaciation on Mount Baker, Washington State, USA

Abstract

The relation between radiocarbon-dated tephras and glacial moraines on the south flank of Mount Baker, Washington, records evidence of an early Holocene glacier advance. Scoria that erupted from a local cinder cone 8420±70 14C yr BP (9450±100 cal yr) occurs immediately in front of, but not on, a complex of moraines overlain by Mazama ash. Radiocarbon ages of 7670±130 14C yr BP (8415±110 cal yr) and 7045±65 14C yr BP (7890±90 cal yr) were obtained from charred wood below the Mazama ash and above till of the moraines, bracketing the age of the glacial advance between ∼7700 and 8400 14C yr BP (∼8400 and 9450 cal yr). Well-preserved Little Ice Age moraines occur proximal to the maximum Holocene positions. Assuming that precipitation regimes were similar, depression of former equilibrium line altitudes suggests that climate during the early Holocene event was at most ∼2°C cooler than present, and ∼0.5°C cooler than the Little Ice Age.