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Have you ever tried to keep track of all the pieces while playing 3-dimensional chess? Imagine if the 4th dimension—time—was included, and the goal was to understand the evolution of the entire Greater Yellowstone Geoecosystem! That's an apt analogy for the 55-year research career of USGS Scientist Emeritus Ken Pierce.
Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Lisa Morgan and Pat Shanks, emeritus research geologists with the U.S. Geological Survey; Cathy Whitlock, Regents Professor in the Department of Earth Sciences at Montana State University; Steve Colman, Director and Professor Emeritus of the Large Lakes Observatory at the University of Minnesota Duluth and Adjunct Scientist at Woods Hole Oceanographic Institution; and Joe Licciardi, Department Chair and Professor of Earth Sciences at the University of New Hampshire.
Ken was hired by the USGS in 1963 after earning degrees from Stanford (BA, 1959) and Yale (Ph.D., 1963). Unraveling Yellowstone's geologic complexities has been Ken's passion since he began working there in 1965, and it continues to be so! Meticulous observations and careful field work have supported his overarching approach to geology: trying to understand what, why, how, and when.
Ken's first assignment was to map the poorly understood deposits left by glaciers in Yellowstone. In this assignment, he helped to produce the first numerical ages of glacial moraines in the western U.S. That landmark study showed the last two major glaciations in Yellowstone, the Bull Lake and Pinedale, were about 140,000 and 22,000 years old, respectively, coinciding with the Illinoian and Wisconsin Glaciations in North America.
Ken recognized that the Bull Lake glaciation was more extensive to the south and west than the Pinedale in the Yellowstone region. He discovered the earliest Pinedale glaciers initially flowed southward from the Absaroka-Beartooth Uplift into the Yellowstone Caldera, depositing thick glacial moraines. His mapping demonstrated early Pinedale glacial buildup occurred on the Yellowstone Plateau (YP), and ice flow later reversed from south to north over the crest of the Washburn Range into northern Yellowstone and beyond. Further mapping showed, in the interval between Bull Lake and Pinedale glaciations, the center of Yellowstone's ice mass shifted toward high terrain to the northeast, a region Ken referred to as the Yellowstone Crescent of High Terrain (YCHT).
Glaciation in Yellowstone was dramatically different from elsewhere in the Rocky Mountains. Why? Ken deduced that the Snake River Plain (SRP) acted as a low-lying conduit channeling storms from the Pacific Northwest to the YP and YCHT, stimulating a tremendous increase in precipitation. Combined with high heat flow and high rates of seismicity, this explains why Yellowstone has more geothermal features than anywhere else in the world.
Ken's questioning of why areas covered by Bull Lake Glaciation differed from those of Pinedale Glaciation, and why Yellowstone is topographically so much higher than its surroundings, led to his pioneering work on the Yellowstone Hotspot. Ken combined recent work on the progression of ages of volcanism becoming younger from southwest Idaho along the SRP northeastward to Yellowstone with his meticulous mapping of faulting and topographic uplift likewise becoming younger to the northeast—this was the basis for understanding Yellowstone's origin as a hotspot!
Ken's focus on the track of the hotspot and on changes in the Yellowstone landscape led to his work on "heavy breathing" of Yellowstone Caldera—recurring episodes of uplift and subsidence. Sediment cores and stratigraphic sections along the Yellowstone River revealed gravels deposited about 2,850 years ago and evidence of high erosive power. Ken and his coworkers deduced the river then was flowing much more vigorously than today, which they attributed to a period of profound uplift of its source area in Yellowstone Caldera. Further study revealed changes in shoreline levels north of Yellowstone Lake related to uplift and subsidence of the caldera over the past 14,000 years.
Through these discoveries, Ken brought understanding of Yellowstone's glaciations full circle—it turns out that subsidence and uplift in the YP-SRP are essential to understanding complex facets of Yellowstone's recent glaciations, as is Yellowstone's hotspot origin! Deformation of Yellowstone Caldera is evident in the distribution of the Bull Lake Glaciation where the topography was actively subsiding in the trailing western part of the hotspot, while the distribution of the younger Pinedale glacial deposits was affected by active uplift on the eastern leading edge.
For over 50 years, Ken Pierce has been a leading and humble contributor to what we know about Yellowstone and, more fundamentally, about geologic processes that inform the Yellowstone Volcano Observatory's ability to assess and respond to modern-day activity. His findings through state-of-the-art geologic field mapping, geomorphology, geochronology, and solid-earth physics are guideposts for current research. His popular books, Interpreting the Landscape of Grand Teton and Yellowstone National Parks, Recent and Ongoing Geology (Good and Pierce, 1996, 2010) and Creation of the Teton Landscape, a Geological Chronicle of Jackson Hole and the Teton Range (Love, Reed, and Pierce, 2003) have introduced the public to the geologic wonders of the Greater Yellowstone Geoecosystem. In addition, Ken is an unselfish researcher who has shared his knowledge and mentored many younger geoscientists. He is emblematic of what it means to be a true public servant and a scientist working with "eyes wide open".
