Ryane, C., Menounos, B., Osborn, G., Clague, J., Davis, P.T., Reidel, J., Scott, K., Tucker, D. and Clark, D., 2008, Holocene glacier fluctuations on Mt. Baker, Washington USA: Canadian Geophysical Union Annual meeting

Holocene glacier fluctuations on Mt. Baker, Washington USA

We use radiocarbon ages and tephrochronology to refine the timing of Holocene glacier fluctuations on Mt. Baker, an active stratovolcano in the Cascade Mountains of Washington. Previous workers suggested that glaciers achieved positions more extensive than those of the Little Ice Age on the volcano’s south flank between 8850 and 6800 14C yr BP, based on the existence on ridges interpreted to be moraines, and on the distribution of SC (8850 14C yr BP) and Mazama (6800 14C yr BP) tephras. Our finding are at odds with the claim of extensive early Holocene advances since our mapping and microprobe data show that the surfaces of these ridges are older than 8850 14C yr BP. A glacial origin of these ridges is also questionable since many are rock cored and are morphologically similar to bedrock structures that are common on stratovolcanoes. In addition to our work on Mt. Baker’s south flank, we also examined the lateral moraines of Easton, Deming, and Coleman glaciers. Many of these landforms are composite moraines; successive, more extensive advances deposited younger till on top of older moraine crests. Stumps in growth position and wood mats demarcate some of these individual tills. The earliest evidence for Holocene glacier expansion on Mt. Baker is preserved in the east lateral moraine of Easton Glacier where the glacier advanced over a vegetated moraine surface at 5200 14C yr BP. Glaciers also advanced at ca. 1750-1600, 940, and 400 14C yr BP. Our research suggests that glaciers on the mountain expanded from minimal extents during the early Holocene and achieved their maximum downvalley positions during the climactic advances of the Little Ice Age.