Robert S. Anderson

I treat the transport of sand and dust by wind as a physics problem involving both fluid and granular mechanics. My past work in eolian transport systems entails field experiments and modeling of the evolution of mixed grainsize ripples in both cross-section and plan view, and laboratory experiments on the dynamics of sand avalanches characteristic of the lee sides of dunes. At present research of graduate student Kelly Kochanski includes the transport of snow and the bedforms that are unique to snow given its cohesive character.

My research on the evolution of large-scale topography was launched in the early 1990s. Work on the Santa Cruz marine terraces and mountains stimulated by the Loma Prieta earthquake is typical of what he hopes to carry out in other tectonic settings, where the topography is produced by tectonic processes, in places by repeated earthquakes, and decays by the action of a suite of geomorphic processes including weathering of bedrock, hillslope processes, and channel incision by both rivers and glaciers. Linkages between these processes lead to the interaction of tectonics and climate to produce topography at many scales, meaning that both climate history and tectonic forcing of the topography become important to constrain. The search for appropriate sites in which there exists sufficient data to constrain process types and rates has taken Anderson and his colleagues, including students, to Utah, the Sierras, Owens Valley, Panamint Valley, Kodiak Island and the Chugach Ranges in Alaska, the Karakoram in Pakistan, Nicoya Peninsula in Costa Rica and the Finisterre Range of Papua New Guinea.

A number of graduate students have been involved over the years in projects related in one or another way to the Santa Cruz coastline and adjacent mountains. The most recent work has focused on the coastal terraces, their timing (see below), and their formation in the face of both uplift of the landmass and attack by waves. Simple modeling in 1-D shows the expected evolution of a benched morphology, but this has been done with little knowledge of detailed effects of the wave forcing. In order to place more quantitative constraints on the relationship of the coastal erosion to the wave climate, former graduate student Pete Adams deployed a seismometer at the Long marine Lab in order to document the amount of energy that actually reaches the cliff. The shaking of the cliff is strongly related to the far-field wave heights and the tidal position, as one would expect. In addition, the orientation of the swell plays a role in that it determines the length of shelf across which the waves dissipate their energy prior to arrival at the coast. We hope to push this effort into the Arctic where rates of coastal erosion are many tens of meters per year.

In many instances the main information gap is timing in the landscape. Anderson has been involved in the development and extension of the use of cosmogenic radionuclides (10^Be and 26^Al in particular) in the extraction of timing in many settings. These have included dating of thin veneers of sediments on strath terraces (Fremont River, Utah; Wind River, Wyoming; Snake River, Wyoming) and marine terraces (Santa Cruz terraces, California), and documentation of bedrock lowering rates in alpine settings (Laramide Ranges, Sierras) and on bedrock river beds (Indus, Pakistan). Work led by former graduate student Lesley Perg was aimed at establishing the ages of the suite of five Santa Cruz marine terraces, which requires dealing with both inheritance and post-depositional bioturbation. The ages obtained are internally consistent, and are surprisingly young, the lowest terrace corresponding to the marine isotope stage 3, about 60 ka. In addition, the need to deal with the inheritance problem in this system led to an investigation of the littoral system. Here we have used cosmogenic radionuclides as tracers of sand within the system. Concentrations in river sands, cliff terrace cover sands, and littoral sands can be used to document the relative contributions of rivers and cliff backwearing to the littoral system, generating a long term average picture of the littoral discharge pattern in the Santa Cruz cell. Work with former graduate student Catherine Riihimaki on the Rocky Flats surface, a major remnant of pediment along the Colorado Front Range has required that we take into account multiple resurfacing events, which are documented in a depth profile of the ratio of 26Al/10Be. We find that the age of the Rocky Flats surface is diachronous, getting younger toward the mountain front where the stream responsible for incising into the surface can still resurface Rocky Flats surface.

A number of graduate students have been involved over the years in projects related in one or another way to the Santa Cruz coastline and adjacent mountains. The most recent work has focused on the coastal terraces, their timing (see below), and their formation in the face of both uplift of the landmass and attack by waves. Simple modeling in 1-D shows the expected evolution of a benched morphology, but this has been done with little knowledge of detailed effects of the wave forcing. In order to place more quantitative constraints on the relationship of the coastal erosion to the wave climate, former graduate student Pete Adams deployed a seismometer at the Long marine Lab in order to document the amount of energy that actually reaches the cliff. The shaking of the cliff is strongly related to the far-field wave heights and the tidal position, as one would expect. In addition, the orientation of the swell plays a role in that it determines the length of shelf across which the waves dissipate their energy prior to arrival at the coast. We hope to push this effort into the Arctic where rates of coastal erosion are many tens of meters per year.

Bedrock incision by fluvial processes, one of the least-understood geomorphic processes, has been a focus of research for some years, starting in the Fremont badlands of Utah, and moving to the Indus River in Pakistan and the Wind River in Wyoming. Anderson and his graduate students have tackled the rates of incision and the processes by which the incision is carried out using a combination of newly developed cosmogenic radionuclide dating techniques, field deployment of datalogger-based instrumentation, and modeling. Former graduate student GregStock used sediments and speleothems in caves along the western metamorphic edge of the Sierran batholiths as a means of documenting rates of incision over many hundreds of thousands of years. The incision history reveals very high erosion rates from 3 - 1.5 Ma, followed by much lower rates. we interpret these to reflect the passage of a knickzone past the cave sites, having been incited by tilting of the range prior to 3 Ma. The mechanism for tilting is debated, but may result from foundering of an eclogitic dense root from the range that coincides with a change int he natrue of volcanism. In addition, working with former graduate student Catherine Riihimaki and former postdoc Liz Safran, Anderson has modeled the incision of major streams issuing from the Colorado Front Range, showing that these are in a state of transient response to the exhumation of the adjacent edge of the Great Plains.

CU graduate student Mauren Berlin has launched her PhD research on the Roan Plateau of western Colorado, into which many tens of waterfalls have bitten. These were presumably cast off from the Colorado River in a pulse of late Cenozoic incision. The site is wonderful for this sort of natural experiment, as all these knickpoints exist in the same Eocene stratigraphy, and the small scale of the landscape assures that the climate is uniform. In this study we focus on not only the positions of these many knickpoints, but on the processes of waterfall retreat and subsequent cliff recession in the valleys, and the presumably very much lower rate of landscape lowering on the top of the Roan Plateau itself. In the adjacent Book Cliffs in the Cretaceous sandstones, Dylan Ward is modeling the pattern of erosion incited by incision of small streams, and is documenting the rate of cliff recession using cosmogenic radionuclides.

In the late 1990s, Anderson and his graduate students, in particular Kelly MacGregor and Catherine Riihimaki (with significant help from others), began to explore the evolution of higher mountain masses in the face of glaciation. Working on the small Bench glacier near Valdez, Alaska, they documented the meteorological forcing of the glacier, the glaciological response, and the sediment output as a means of constraining the erosion occurring at the bed of the glacier. The target here is understanding of the evolution of the long valley profile in the face of glaciation, which includes the generation of cirques, hanging valleys and fjords. The field work and in particular the detailed evolution of the glacier surface speed field over the summer season, has pointed toward the need to understand the glacial plumbing system and its summer evolution. We demonstrated the great utility of GPS monuments on the glacier itself in documenting the sliding hisotry over a melt season.

This project included modeling the evolution of glacial valley longitudinal profiles. Using a 1D numerical model, we showed that the flattening of glacial valleys is expected, and that the hanging of tributary valleys and the steps in trunk valley floors are straight-forward consequences of tributary systems. This modeling work has now moved into 2D glacial models, in which we simulate the evolution of glaciers on real landscapes (e.g., Yosemite, Kings Canyon, Uintas, Colorado Front Range, San Juans, Colorado [see ...instaar/rmnp page for examples]). The target here is several-fold. First, we wish to determine the climate scenario that allows a best match of the glacial footprint to the existing LGM moraine and trimline data. Second, once we have assured ourselves that the model works well, we will drive glacial histories with ELA histories, and allow the landscape to evolve in the fac e of subglacial erosion. The erosional output from the glacial will be fed to a fluvial model to allow proper coupling of glacial and fluvial systems. This effort has been augmented by analytic work on glacial erosion in which we explain the essential features of glacial long valley profiles using simplifying assumptions of quasi-steady glacial conditions and eroison proportional to ice discharge.

recent work: With CU graduate student Dylan Ward, I am attempting to determine the roles of glaciers in setting the very high relief in the Alaska range and other very high mountain masses of the world. Zack Guido is documenting the ages of moraines and adjacent river terraces in the Animas outlet glacier form the ice cap that occupied the centrak San Juans in the LGM. He is also exploring the degree to which the glacially polished bedrock of the glacial valley itself has been eroded during the last glacial cycle, using the degree to which cosmogenic radionuclides were reset.

Another project just completed focused on the late Cenozoic evolution of the Laramide Ranges and adjoining basins in the western US. This project involved graduate student Catherine Riihimaki, and is collaborative with Liz Safran at Lewis and Clark College. Particular problems treated included the evolution of the smooth high surfaces on the shoulders and peaks of these ranges; the river and glacial profiles that incise the subsummit surfaces; and the timing of and processes involved in the exhumation of the Tertiary sediment-filled basins. The large remaining issue is the cause of the late Cenozoic exhimationof teh Great Plains and other basins adjacent to the Laramide Ranges. This remains a target of our investigation in this region.

Finally, former graduate student Mike Loso began tackling the thorny issue of the role of biology in modulating surface processes. He is thinking about how one might incorporate the role of rodents in transporting sediment on hillslopes, while being faithful to the elements of ecology such as where the animals prefer to live, their subterranean digging patterns, the role of predators in digging out their dens, and so on. We have now developed models of landscape evolution in the face of non-uniform occupation of the landscape by rodents.

• William Armstrong, Research Assistant
• Jill Marshall, postdoc 2015-2017
  • Assistant Professor at University of Arkansas
• Eric Winchell, PhD 2017
• Melissa Foster, PhD 2016
• Katy Barnhart, PhD 2015 in Geological Sciences
• Leif Anderson, PhD 2014 in Geological Sciences
• Andy Wickert, PhD 2014
• Miriam Dühnforth, postdoc 2007-2011
  • Assistant Professor in Geology and Tectonics, LMU Munich
• Dylan Ward, PhD 2010
  • Associate Professor, University of Cincinnati
• Maureen Mason Berlin, PhD 2009
• Nora Matell, MS 2009
• Tim Bartholomaus, MS 2007
  • Assistant Professor, University of Idaho 2016
• Zack Guido, MS 2006
  • University of Arizona Research Scientist, Joint University of Arizona & Columbia University International Research and Application Program (IRAP)
• Mark Kessler, postdoc 2003-2005

"The glacier - rock glacier continuum," CSU Geology departmental seminar, November 2018

"Alpine ice on Earth: Glaicers and their rocky cousins," CU Astronomy departmental seminar, November 27, 2017

"From pure ice to rock-covered ice: the glacier-rock glacier continuum," UWashington Department of Geosciences colloquium, November 2, 2017

"Hillslopes," UWashington Department of Geosciences colloquium, November 3, 2017

"Hills and their evolution: Involving parabolas, exponentials, and hyperbolas," Applied Math, CU Boulder, April 14, 2017

"Hillslopes of Colorado’s Front Range: From frost to trees to gophers to boulders," Potsdam, Germany, January 10, 2017

"Mountains Glaciers and Gold," Breckenridge, November 16, 2016

"Mountains Glaciers and Gold," Fairplay, November 15, 2016

"Evolution of the Colorado Front Range and the relevance of the 2013 storm," Phi Beta Kappa of Colorado, November 12, 2016

"From pure ice to rock-covered ice: the glacier-rock glacier continuum," Crowell Lecture Series, UC Santa Barbara Department of Geosciences, November 2, 2017

"Climate change in our backyard series: Glaciers and rock glaciers in Colorado’s mountains," Fiske planetarium, November 18, 2016

"Dirty Glaciers," INSTAAR, CU Boulder, February 3, 2015

"Edges and blocks matter on hillslopes, rivers, and glacial landscapes," INSTAAR, CU Boulder, December 2014

"Glacial modification of landscapes: From far-flung moraines to roche moutonnee," University of Iowa, October 23, 2012

"Glaciers and the landscapes they modify: Lessons from the Kennicott Glacier, Alaska," Wrangell Mountain Center talk series, McCarthy, Alaska, June 2012

"Glaciers and glacial landscapes: from natural to numerical experiments," U. Texas Austin February 2012

"Edges matter: Erosion of landscapes by migration of edges," INSTAAR, CU Boulder, April 2012

"Of ice-water interactions in Arctic and alpine landscapes: Rapid Arctic coastline erosion and the sliding of glaciers," Caltech, January 2011

"Dominance of thermal processes and their likely acceleration along Alaska's Beaufort Sea coast," National Park Service webinar July 20, 2011

"Glaciers and glacial landscapes," Kennicott Seminar series, Wrangell Mountains and St Elias National Park, June 2010

National Snow and Ice Data Center (NSIDC) February 2009, University of Montana September 2009, Five College Lecture series, Amherst, October 2009

Yosemite Fund, March 2008; Yale, October 2008

INSTAAR, February 2007; Workshop on Climate and Geomorphology, NCAR October 2007

University of New Mexico, 10 February 2006; Wrangell-St. Elias National Park, July 2006; INQUA conference on mountain glaciers, September 2006; Garry Clarke conference, UBC, December 2006

University of Memphis, March 2005; UC Davis, April 2005; EGU, April 2005; India Geological Society, May 2005; CU INSTAAR Mountain Research Station, June 2005; CU Geology, September 2005; Rocky Mountain National Park, September 2005; NSF Earth Science Day, September 2005; University of Michigan, November 2005

Colorado School of Mines, April 2004; Colorado State University, April 2004; Yosemite National Park, June 2004

Stanford, January 2003, Penrose conference Taiwan January 2003, University of Colorado January 2003, Purdue February 2003, UC Santa Barbara February 2003

University of Wyoming January 2002, University of Colorado January 2002, Colorado College April 2002, University of Nebraska Lincoln September 2002, 'Year of the Mountain symposium,' University of Colorado November 2002, Gilbert Club December 2002

USGS Marine Geology February 2001, University of Arizona February 2001, Duke November 2001, MIT November 2001, INSTAAR December 2001

UC Santa Barbara February 2000; Caltech February 2000

William and Mary March 1999; Arizona State April 1999

UC Davis January 1998; University of Alaska Fairbanks June 1998; University of Oregon October 1998

Scripps. January 1997; USC. January 1997; Harvard. March 1997

Stanford. May 1996; UC Riverside. April 1996; Penn State. April 1996; U. Washington. May 1996

University of Wyoming. February 1995; University of California Santa Barbara. March 1995; Franklin and Marshall College. October 1995; Penn State. October 1995; Lehigh University. October 1995

Caltech. February 1994; Stanford. March 1994; UC Berkeley. March 1994; MIT. March 1994; Oregon State. April 1994

San Jose State. January 1992; University of Southern California. November 1992

Williams College. (3 talks) Geology, Environmental Studies. February 1991; Duke University. Geology. February 1991; University of Wyoming. November 1991; University of Texas, Austin. November 1991

UC Berkeley. April 1990; UC Santa Barbara. January 1990

Bowdoin College. January 1988; UC Santa Cruz. February 1988

UCLA. October 1987; Johns Hopkins. April 1987