KEN PIERCE'S BENCHMARK CONTRIBUTIONS TO WESTERN U.S. GLACIATION (Invited Presentation)

Ken Pierce was the quintessential field geologist who followed in a long tradition of U.S.G.S. geologists in mapping Quaternary deposits and landforms. However, Ken's real mark in the field reflects his fundamental contributions to our understanding of western U.S. glaciation that advanced the field to the modern era of numerical dating and ice-climate interactions. Ken first applied novel dating methods to advance the chronology of western U.S. glaciation beyond the longstanding relative approach to one based on numerical methods. His 1976 paper using calibrated rates of obsidian hydration represented a paradigm shift in our understanding of Pinedale and Bull Lake Glaciation, which for so long had been pigeon holed into late and early Wisconsin ages, respectively, based on the influential work from the southern margin of the Laurentide Ice Sheet. Ken's work with Steve Colman on weathering rinds, especially their efforts to calibrate rind development, further advanced our understanding. Ken's work on U-series dating of perched travertines, combined with his earlier work with obsidian hydration, was the first to identify a millennial-scale signal in Pinedale glaciation. Ken was then quick to collaborate with Joe Licciardi in applying cosmogenic nuclide dating to the Yellowstone ice cap moraines, providing a remarkable temporal framework that reveals highly intricate and complex responses of the ice cap to climate change and perhaps internal ice dynamics. Ken's second benchmark contribution is his reconstruction of the Yellowstone Ice Cap as remarkably told in his Kirk Bryan Award winning USGS Professional Paper 729. Here for the first time, Ken combined his detailed mapping with a physically based understanding of ice dynamics to provide an unprecedented understanding of how the ice cap evolved through the last deglaciation. In doing so, Ken moved the field beyond simple moraine mapping to one where Quaternary geologists needed to think about the physics of the glaciers that formed the moraines and their relation to climate change. We now routinely see new western U.S. cosmogenic nuclide chronologies and attempts to understand the relation of these well-dated glacier fluctuations to climate, including through use of numerical models. Each of Ken's contributions paved the way for this new work.