2018 Kirk Bryan Award

Presented to Karen B. Gran

with Noah Finnegan, Andrea L. Johnson, Patrick Belmont, Chad Wittkop, and Tammy Rittenour

for: 2013. Landscape evolution, valley excavation, and terrace development following abrupt postglacial base-level fall. GSA Bulletin 125(11/12) 1851-1864.

Citation by Amy East and Andrew Wilcox

The paper by Karen Gran and co-authors represents a comprehensive, creative approach to a suite of problems that have long been central to Quaternary Geology and Geomorphology investigations: postglacial landscape evolution, knickpoint migration, fluvial terrace development, and modern, anthropogenically altered watershed processes. Their study, focusing on the Le Sueur watershed, Minnesota, is a uniquely thorough contribution to two themes at the forefront of earth-surface-process science today: understanding landscape evolution in response to changing climate, and understanding anthropogenic effects on landscapes and critical-zone processes. Gran and her colleagues evaluated landscape change (and drivers of change) at time scales spanning late Pleistocene deglaciation, Holocene climatic variations, and modern agricultural expansion and intensification. They effectively linked a close, careful study of their field area to broad-scale surface-process problems to provide insights into, for example, how knickpoints propagate in transport- vs. detachment-limited systems; the interaction among lateral and vertical erosion and implications for terrace development; and downstream grain-size variation. Gran et al. addressed classic problems using state-of-the-art remote sensing techniques and geochronology, as well as more traditional field geomorphology, fitting a vast amount of work into one paper. They have thereby tackled the considerable challenge of understanding how transient systems evolve over a wide range of time scales. This paper not only represents a significant scientific advance in understanding landscape evolution, but also relates clearly to modern land use and watershed management applications. Such a merging of fundamental and applied science is what earth scientists generally know that our field needs to accomplish, and that most of us aspire to, but that is rarely achieved as comprehensively as in this study.

2018 Kirk Bryan Award — Response by Karen B. Gran

I want to thank Amy East and Andrew Wilcox for their kind words in support of our research and for nominating our paper for this award. We are deeply appreciative of the recognition and truly honored to be receiving the Kirk Bryan Award. We want to thank the Quaternary Geology and Geomorphology Division for making this award possible, and are humbled to be joining the ranks of a very illustrious group of geomorphologists and Quaternary scientists.

This paper was truly an integrated effort, and I want to make sure my co-authors and collaborators get the recognition they deserve. Andrea Johnson was my first graduate student. She spent countless hours paddling the rivers in southern Minnesota, and it was her Master’s thesis work on terrace history that formed the initial core of this paper. Patrick Belmont was the first to point out that our rivers were not normal, and they had a major knickpoint working its way upstream. He led the Lewis & Clark style expeditions down the Le Sueur, collecting in-stream field data that helped anchor the modeling work that was to follow, documenting among other things, the pervasive downstream coarsening seen in our channels. Noah Finnegan was the mastermind behind the numerical modeling, taking the dataset amassed in the field and using it to start answering questions about how a transient system like the Le Sueur carved its profile and valley over time. Tammy Rittenour provided excellent geochronology work, a necessary part of any project reliant upon rates and dates. Chad Wittkop first recognized a major stream capture event in our watershed, which helped explain gaps in our terraces and patterns in the ages of them. This paper would not have happened without everyone’s contributions. In addition to the co-authors listed, we want to recognize the efforts of Carrie Jennings, Stephanie Day, Peter Wilcock, and a large number of student field assistants for their help throughout the project.

Funding for this research was provided by NSF through the National Center for Earth-surface Dynamics and the Minnesota Pollution Control Agency. We appreciate the MPCA’s progressive stance on environmental issues and desire for science-based decision-making. They not only got this project up and running, but they also listened to our results and helped put science into policy.

And finally, I hope our research inspires other people who work in post-glacial rivers to recognize the unique possibilities that come from these very young landscapes that are still actively responding to perturbations from the last glaciation. These transient systems can tell us a lot about how rivers evolve in more complex environments, and I will point out that most tills erode faster than bedrock and all of our terraces are all young enough for radiocarbon. Try not to overlook the rivers of the upper Midwest – there is a lot we can learn from them.

On behalf of all of my co-authors, thank-you very much for this honor.

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