A late glacial and holocene chronology of the Castner Glacier, Delta River Valley, Alaska

• Main Author: Howley, Michael W
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2008
• Subjects: Geology; Hydrology; Delta River; Ela; glacier; Alaska
• Online Access: https://scholars.unh.edu/thesis/421; https://scholars.unh.edu/context/thesis/article/1420/viewcontent/1463225.pdf

New field mapping of surficial deposits near the Castner Glacier, Alaska has identified three distinct moraine complexes beyond the current glacier margin, denoting at least three separate intervals of glacial advance or stillstand. The timing of moraine stabilization and ice retreat was determined by cosmogenic 10Be surface exposure dating for the two older moraines along with lichenometric measurements for all three moraines. Surface exposure ages indicate the timing of ice retreat after the late Wisconsin maximum at 14.7 +/- 0.7 ka (n = 4, k-years before present), and identify the intermediate moraine as corresponding to the Little Ice Age (LIA) at 1627 +/- 32 years AD (n = 2). Lichen measurements from the youngest moraine indicate an age of 1842 AD, corresponding to the late LIA. The lichen data agree to within 50 years of exposure dating results for the older LIA moraine complex, but greatly underestimate the timing of Late Pleistocene ice retreat, indicating a limit of the useful time range for lichen dating using Rhizocarpon (sp.) in this region. There is no evidence for a Younger Dryas re-advance of the Castner Glacier, indicating that the glacial response to this climate fluctuation was less pronounced than that caused by LIA cooling. The increase in elevation of the equilibrium line altitude (ELA) of the Castner Glacier from the late LIA to the present is 120 +/- 20 m. The climate change that could force this rise in ELA is reconstructed to be either a 0.68 to 0.81°C increase in JJA temperature, or a decrease of 8.9 to 12.5 cm H 2O annual accumulation.