Phillip H. Larson

Earth Science - Geomorphology - Quaternary Science

Research Interests

Because my teaching and mentorship are closely intertwined with my research, my research interests and objectives often guide my holistic activities as a Teaching Scholar and university professor.  Thus, to understand my teaching and my work with students, I must also explain my expertise and interests in research within geoscience/earth science.  My research objectives and pursuits lie in understanding landscape evolution and paleoenvironmental change through investigating geomorphic processes that transform the surface of our planet, sediments deposited by those processes, and landforms produced by those process.  Thus, I am a geomorphologist and Quaternary scientist (the Quaternary is the last 2.6 million years of Earth’s geologic and environmental history). I constrain my research in the sub-disciplines of desert-arid geomorphology/environments, fluvial (rivers) geomorphology, aeolian (wind-blown) geomorphology, and natural hazards that result from geomorphic processes (e.g. landslides, erosional processes, floods, etc.). Much of this work has been broadly focused on drainage basin reorganization and geomorphic system response following perturbations to the fluvial system (i.e. allogenic perturbations - climatic change, base-level fall/rise, anthropogenic activities, tectonic forcing, and autogenic perturbations – substrate variability, complex response, coupled-geomorphic system interactions).  These perturbations can also transform relatively stable landscapes, with low potential energy, into unstable landscapes with high potential energy that often transfers to kinetic energy as the landscapes are transformed by erosional processes through time – often producing various types of natural hazards (e.g. landslides).   In conducting my research, I take a field-focused approach to data collection through utilizing my expertise in geochronologic dating techniques (e.g. optical stimulated luminescence dating, cosmogenic nuclide dating, radiocarbon dating), geospatial data collection (GPS/GNSS, field mapping), and geophysical methods (ground penetrating radar).  I work closely with world renowned experts both nationally and internationally in these methods and in conducting the research in our field. Thus, my students are trained in these same field-focused methods and in this same intellectual realm of scientific inquiry.

Understanding the cascading sequence of events that propagate through a drainage basin following abrupt base level lowering has been the overriding theme thus far. For example, in studies in the southwest United States, my research has been part of a larger collaborative effort to understand how rivers are “born” following an extensional tectonic regime (Basin and Range Orogeny) that reversed regional drainage network paths.  This work requires understanding how transverse drainage networks develop following reversal to integrate hydrologically and structurally closed, or endorheic basins.  Upon establishment of transverse river systems, episodes of base level lowering within these endorheic basins occurs. This is a result of the ongoing adjustment of the drainage network to a new base level condition. Consequently, an enormous shift of erosional foci and sediment deposition occurs as these systems evolve towards a new equilibrium condition.  The sediment deposition that results from integration processes are important deposits for understanding groundwater resources in an arid landscape that hosts rapidly growing metropolitan areas like Phoenix, AZ.  Ongoing adjustment to these basin integration processes is reflected in the present landscape as it contains diagnostic landforms (stream terraces, incised pediments and alluvial fans, dissected basin fill) recording this dynamic change.  These are the landforms I study through morphological and sedimentological analysis, geochronological dating, relict landscape reconstruction, and other techniques.  Ultimately, this work has culminated in a Special Issue that I am serving as Lead Editor of in the prestigious journal Geomorphology.  In this special issue I am an author on four new research papers and served as reviewer and editor on ten peer-reviewed articles that comprise the Special Issue: Drainage Integration in Extension Tectonic Regimes (see: https://www.sciencedirect.com/journal/geomorphology/special-issue/10769TKL6KQ).  This special issue compiles work from my colleagues and collaborators from around the world – working in the Apennines, South Korea, and the southwest USA.  Contributions to it include scholars from institutions in South Korea, Norway, Arizona, California, Minnesota, and New Mexico.

Another example of my current research focuses on the landscape evolution of the upper Mississippi River basin (UMRB). The two foci of this research lie in post-glacial fluvial system response to base level fluctuations and aeolian deposition at and post last glacial maximum (LGM). Recent work with my colleagues has focused on the Chippewa River, Wisconsin, and just received the GK Gilbert Award from the American Association of Geographers in 2019.  This award is given to “a single significant contribution to the published research literature in geomorphology during the past three years.”  It is the highest honor bestowed to a piece of research in geomorphology by the American Association of Geographers (see: https://aag-gsg.org/awards/gk_gilbert_award/). In addition to this work, ongoing research is focused on understanding the timing and evolution of the Minnesota River valley (formerly glacial River Warren - Lake Agassiz outlet) and investigating tributary systems (e.g. Cannon River, Zumbro River, Whitewater River, St. Croix River, etc.) to the Mississippi in an attempt to build a holistic model of fluvial system response to base level fluctuations following regional deglaciation.   In this work, I closely collaborate with Dr. Andrew Wickert (University of Minnesota) and Dr. Douglas Faulkner (UW-Eau Claire). As a whole, this work has significant importance to rapidly melting glacial and periglacial landscapes around the world as our climate continues to warm.  As glaciers rapidly melt across the planet, similar processes will impact landscapes in those locations.  Thus, my work with my colleagues can help us understand and predict what may happen in those landscapes as climate change continues on. 

The second research foci in the UMRB, the significance and nature of aeolian deposition post LGM, ranges from sandy deposits (e.g. parabolic dunes, sand ramps, climbing dunes, sand stringers, sand sheets) to variable thicknesses of loess (fine grained sediments, silt). In this work, we are attempting to understand the mechanisms behind aeolian deposition and the paleoenvironmental significance of these deposits – likely primarily tied to “melt-out” of permafrost in the region in the early Holocene.  This, too, has significant implications to understanding landscapes, like the arctic, where permafrost is rapidly melting due to climate change.  The ancient aeolian deposition we are investigating may also have parallels with modern environments where similar process are likely to occur as permafrost is melting-out in the Arctic, alpine, and Antarctic regions of the world today.

New interdisciplinary work and expansions to ongoing work are underway. These research initiatives will drive much of my work for the years to come and represent the culmination of eight years of prior work that laid the foundation for the “big picture” research questions I seek to answer.  This includes a ~$1.25-1.3 million National Science Foundation CNH2 proposal being compiled related to the geoarcheology of the upper Mississippi River basin, USA.  This work is trying to understand native people's interactions with and responses to the changing environmental and geomorphic systems through the Holocene (last 11.7 thousand years) and prior to Euro-American settlement.  As the environment evolves, so do people, and this has occurred throughout time.  I believe this work is the natural progression of all that I have pursued thus far and has broader implications related to Native American cultural heritage preservation, understanding the history of Native cultures in this region, and better understanding our (humanity) connection to our environment. This research initiative is the underpinning for the AGES Laboratory (now EARTH Systems Laboratory) I co-founded with Dr. Ronald Schirmer in 2016.  Another example of ongoing and future research objectives include a $550,000 NSF EAR proposal being compiled to understand the landscape evolution of the Minnesota River valley, the nature of catastrophic floods that formed it, and how native peoples interacted with this valley through time.  Lastly, new research in Patagonia, Argentina is underway in collaboration with Dr. Wickert (University of Minnesota) related to deglaciation and the evolution of the Rio Santa Cruz, a river flowing through a semi-arid landscape of southern Argentina and that drains the Southern Patagonian Icefield – an area with some of the fastest rates of glacial melt on Earth.  All of these ongoing and future research proposals contain funding for graduate and undergraduate students (e.g. stipends, tuition waivers, field expenses, etc.) in order to facilitate the Teaching Scholar approach to my career.

If you have any questions or interests in my research, please don't hesitate to contact me! phillip.larson@mnsu.edu or 5073892617.
Or, please visit:

Earth Surface Process Group: https://umn-earth-surface.github.io/people/

 



View Phil Larson research locations in a larger map

Ongoing Research Project Example - Geomorphic Map of the lower Salt River and confluence with the Verde River, central Arizona. (Larson, P.H., Dorn, R.I, Douglass, J., Gootee, B.F., Arrowsmith, R. (2010). Stewart Mountain Terrace: A New Salt River Terrace with Implications for Landscape Evolution of the Lower Salt River Valley, Arizona. Journal of the Arizona-Nevada Academy of Science 42 :26-35)

The Salt and Verde Rivers of Arizona serve as wonderful natural laboratories for study and model building related to how Basin and Range rivers become through-flowing drainages. Millions of years ago extensional tectonic forces created a landscape full of internally drainged basins bounded by small mountain ranges. Sometime in the more recent past (<2 million years ago), rivers like the Salt and Verde began to integrate these enclosed basins when they first arrived from the transition zone (between the Colorado Plateau and Basin and Range). Today, I am using these two drainage systems to try and determine the when, why and how of integration. This research is being conducted in hopes that my colleagues and I can establish a model for the integration process in similar extensional regions.

Currently we are processing samples for both surface exposure and burial dating using cosmogenic nuclides (10Be/26Al) from the stream terrace sediments throughout these basins. This will help us understand the chronology and help establish process rates throughout region. GIS modeling of pediment response to baselevel fall is also underway and this will help us constrain the rates of piedmont adjustment to integration and post-integration basin evolution.

A separate project website is in development regarding this research and will convey our results to the public after it is published


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“Yosemite Valley, to me, is always a sunrise, a glitter of green and golden wonder in a vast edifice of stone and space.” - A. Adams