SuzanneAnderson

  • Professor
  • GEOLOGICAL SCIENCES
Address

Office: SEEC N141b

Geomorphology • Weathering • Hydrology • Critical Zone

Bio

I am a geomorphologist interested in processes that shape the Earth’s surface. I have been at the University of Colorado and a member of INSTAAR since 2003. The eruption of Mount Saint Helens in 1980, which exploded at a personal inflection point in my life, opened my eyes to geosciences as a discipline. Despite that volcanic start, I was drawn into the field of geomorphology by the dynamic faculty and students at the University of Washington, where research on hillslopes, fluvial and periglacial processes, glacial geology, and glaciology were thriving. My MS thesis under the supervision of Bernard Hallet employed lab experiments and field work in Svalbard to study upfreezing and periglacial patterned ground. After a brief stint working at Caltech (Sam Epstein's stable isotope lab and briefly with Barclay Kamb’s glaciology team) and teaching at Pasadena City College, I moved to Santa Cruz, California and began a PhD at UC Berkeley. My dissertation on chemical geomorphology (my addition to jargon) was one of several that came out of Bill Dietrich and Keith Loague’s Coos Bay (Oregon) project on the hydrology, weathering, and slope stability of an unchanneled valley. I merged my interests in glaciers and weathering in an NSF Earth Sciences Post-Doctoral Fellowship at the University of Wyoming, where I worked with geomorphologist/glaciologist Neil Humphrey (and friend from U Washington days) and with geochemist Tim Drever. I participated in workshops that created the Critical Zone Exploration Network, a forerunner of NSF’s Critical Zone Observatory Program. I led a fantastic, interdisciplinary team in the Boulder Creek Critical Zone Observatory from 2007 until NSF terminated the CZO Program in 2020. I co-authored the textbookGeomorphology: The Mechanics and Chemistry of Landscapeswith husband Bob Anderson in 2010, and the children’s book The Living Landscape: Discovering the Critical Zonewithartist Eric Parrish in 2022.

News about Suzanne

Research

Earth is a rocky planet, whose outer surface is burnished over time by physical and chemical weathering at the rock/atmosphere boundary.

My research interests lie in understanding the effects of weathering, and the processes that drive weathering. These topics lie at the heart of geomorphology and surface process research, as rock weathering sets the stage for the landscape sculpting processes of erosion. Like a dog chasing its tail, feedbacks between process and form make it difficult to identify a starting point. The movement of water and actions of weathering and erosion processes set the architecture of the interface between the atmosphere and the rocky lithosphere, which in turn affects water flow and erosion. Chemical alteration of rock in surface environments contributes to geochemical cycles, connecting the local—even on a miniature scale—to the global. Soils accumulate where the balance between weathering and erosion builds capital of this life-supporting residue. I’m particularly drawn to landscapes affected by ice, whether that ice is in the form of glaciers, rock glaciers, or ground ice.

The notion that intertwined actions of surface energy inputs, rock decay, gravitational pull, water, and living organisms shape the Earth’s surface is articulated by defining the surface as the “critical zone.” I worked for more than a decade to define critical zone science as an integrative approach to understanding habitable environments (Anderson et al., 2004, Eos Transactions, AGU; Anderson et al., 2007, Elements; Anderson et al. 2008, Mineral. Magazine; Brantley et al., 2017, Earth Surf. Dynam.). I led a successful bid for one of the original Critical Zone Observatories (CZO) funded by the National Science Foundation in 2007. Theoperated until 2020 and involvedsome 15 faculty and senior researchers in interdisciplinary study of the architecture, function, and future of the critical zone, using the Colorado Front Range as a natural laboratory for this exploration. We trained approximately 37 graduate students, 10 post-docs, and many dozens of undergraduate students.

Research areas

Water is required for chemical alteration of rock to proceed. Chemistry of stream runoff would seem to be a straightforward means of measuring on-going chemical weathering processes. The picture is clouded somewhat by the fact that water flow paths contributing to runoff vary with changing discharge. Thus, interpreting chemical weathering from runoff involves analyzing watershed hydrology. The Gordon Gulch watershed in the Boulder Creek CZO was an excellent laboratory in which to examine changing hydrologic conditions and their connection to hydrochemistry. The stream channel runs east-west, and thus the catchment is dominated by north and south-facing aspect hillslopes. At ~2500 m altitude in the Colorado Front Range, the differing energy balance on these pole and equator facing hillslopes translates into a difference in winter solar radiation of nearly a factor of 3 and consequently entirely different snow regimes (Anderson et al., 2021, AGU Geophys. Monograph 257, Ch. 13). We showed that water flowed rapidly through the soil matrix on north-facing slopes during snowmelt, while water flow was episodic and dominated by preferential flowpaths on south-facing slopes (Hinckley et al., 2014, Hydrol. Process.), and that heterogeneity continues to dominate hydrologic behaviors on both slopes during summer rains as well. Modeling these flow regimes, Langston et al. (2015, Earth Surf. Process. Landfms.) concluded that greater water delivery to the bedrock weathering front was accomplished on north-facing slopes.

Two boundaries are important in the interface region between the lithosphere and the atmosphere: 1) the lower boundary between fresh rock and weathered rock—the weathering front, and 2) the upper boundary between ground and air—the surface topography. While we can measure surface topography in exquisite detail with LiDAR, imaging the deep weathering front is much more difficult. Consequently, understanding how the deep weathering front propagates is a frontier in critical zone science. Seismic refraction imaging in the Boulder Creek CZO showed that the depth to fresh rock is ~2 m greater under north-facing slopes than under south-facing slopes in Gordon Gulch (Befus et al., 2011, Vadose Zone J). The apparent slope-aspect control on weathering front depth (Anderson et al., 2021, AGU Geophys. Monograph 257, Ch. 13) has inspired investigation of processes that may be responsible. As the weathering depths are on the order of 10 m, and total denudation rates are ~30 m/Myr, the full depth of the weathering profile integrates over a period of ~300,000 years (Foster et al., 2015, GSA Bull). This timescale implies evolution during Quaternary glacial climates, and consequently we explored a frost-cracking model for weathering front propagation (Anderson, RS et al., 2013, Earth Surf. Process. Landfms) and a climate-driven chemical weathering model (Anderson, RS et al., 2019, Hydrol. Process.) Analysis of soil pits and shallow rock cores shows minor chemical alteration of the rock, and detectable differences in rock strength by slope aspect (Anderson et al.,2021, AGU Geophys. Monograph 257, Ch. 13). More work can be done!

The connection between weathering and erosion in shaping critical zone architecture was a major theme of the Boulder Creek CZO. A significant feature in the Boulder Creek watershed is the canyon Boulder Creek has carved through crystalline rock in the Front Range. We hypothesize that the canyon resulted from upstream migration of a knickpoint in the river, spawned by exhumation of the Plains (Anderson et al., 2012, Comptes rendus- Geoscience). An examination of landsliding and debris flows in the 2013 "storm of the century" that ravaged the Colorado Front Rangeshowed that landslides and debris flows were produced exclusively from the steep (>25°), colluvium-mantled slopes lining the canyons, rather than the more rocky locations (Anderson, SW et al., 2015, Geology). Consequently, the production of colluvium on rocky slopes stands as an important precursor step to landsliding and debris flow generation. Moreover, Rossi et al. (2020; Geophys. Res. Lett.) found that storm runoff in the Front Range is not only controlled by storm characteristics (which vary with elevation), but also by watershed characteristics, e.g. rockiness(which presumably varieswith elevation as well). Distinguishing where slopes are rocky, and where they are soil mantled will have utility in predicting flash flood hazard (from rocky areas) and landslide hazards (from soil-mantled areas) in regions beyond our Front Range landscape.

Glaciers, rock glaciers, and permafrost all affect landscapes in important ways. The weathering profiles, soils, and topography of most modern landscapes have formed over thousands to hundreds of thousands of years of weathering and erosion, and hence are very much the product of the climate of the Quaternary and Holocene. My current research focuses on understanding hydrology alpine areas where glaciers and rock glaciers (Anderson and Anderson, 2025, Geology) hold ice that affects the runoff production and flowpaths of water. I have also worked on the Canning River on the North Slope of Alaska to address the carbon budget of a river corridor in permafrost terrain.

Education

  • PhD in Geology: University of California, Berkeley, 1995
  • MS in Geological Sciences: University of Washington, 1987
  • BS cum laude in Chemistry: University of Puget Sound, 1979

Awards

  • Fellow, American Geophysical Union, 2021
  • G.K. Gilbert Award in Surface Processes, American Geophysical Union, 2020
  • Fellow, Geological Society of America, 2019
  • Certificate of Recognition, International Association of GeoChemistry, 2012

Current students

  • Cole Cochran, MS Geological Sciences, 2024
    • Floodplain carbon storage: Soil organic carbon, surface age, and vegetation in an icy river corridor
  • Marisa Repasch, Postdoc, 2022-2024
    • NSF Polar Programs Post-doctoral Fellow, Linking the physical and chemical drivers of carbon cycling in Arctic source-to-sink systems
    • Co-advised with Shaily Rahman
  • Claudia Corona,PhD Geological Sciences, 2023
    • Impact of extreme precipitation events on the water table and groundwater recharge
    • Co-advised with Shemin Ge
  • Lauren Salberg, MS Geological Sciences, 2021
    • Coupling field data and a flow model to characterize the role of groundwater in a montane, semi-arid watershed, Gordon Gulch, Colorado
    • Co-advised with Shemin Ge
  • Noah Hoffman, MA Geography, 2019
    • Lithogenic mixing model approach identifies saprolite as the source of inorganic colloids in a granitoid catchment
  • Matt Rossi, EarthLab Postdoc, 2016-2018
    • Precipitation extremes and landscape evolution. Now EarthLab Research Associate.
  • Joe Mills, PhD Geography, 2016
    • Water chemistry under a changing hydrologic regime: Investigations into the interplay between hydrology and water-quality in arid and semi-arid watersheds in Colorado
  • Chris Mavris, Postdoc, 2012-13
    • Swiss National Science Foundation Postdoctoral Fellow, Global warming induced vegetation changes and their effects on mineral weathering in a cold-dry and alpine environment (Wind River Range)
  • Patrick Kelly, MA Geography, 2012
    • Subsurface evolution: Characterizing physical and geochemical weathering in bedrock of Gordon Gulch, Boulder Creek Critical Zone Observatory
  • Eve-Lyn Hinckley,Postdoc, 2009-11
    • NSF Earth Sciences Post-doctoral Fellow, An integrated approach to study the interactions between hydrologic response and nitrogen biogeochemistry
  • Susan Riggins, PhD Geography, 2010
    • The production and evolution of mobile regolith: Modeled soil production and measured chemical weathering.
  • Zanden Frederick, MA Geography, 2008
    • Water and solute export from the Yukon River and its tributaries
  • Cynthia Cacy, MS Environmental Studies, 2006
    • Chemical weathering in the loess-mantled landscape of the Matanuska Valley, Alaska

Courses taught

  • GEOL 4241: Principles of Geomorphology
  • GEOL 3090: Science Writing
  • GEOL 1170: Our Deadly Planet
  • GEOL 1010: Exploring Earth
  • GEOL 5700: The Cryosphere
  • GEOL 5702: Gemorphology Seminar

Publications

For additional publications, see Suzanne's.