Interdisciplinary Studies in the Critical Zone, Boulder Creek Catchment, Front Range, Colorado

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What: This project will join a large interdisciplinary study (Boulder Creek Critical Zone Observatory: Weathered profile development in a rocky environment and its influence on watershed hydrology and biogeochemistry—NSF 0724960) directed by Suzanne Anderson, University of Colorado and Institute for Arctic and Alpine Studies (INSTAAR). The “observatory” will consist of 3 small, instrumented sites in the Boulder Creek basin: (1) a steep alpine area in the Boulder watershed; (2) a forested, mid-elevation catchment developed in deeply weathered materials, and (3) a steep, lower-elevation basin where surficial deposits are of variable thickness.

When: July 16 – August 14, 2008

Where: Colorado

Who: 3 students and Professor David P. Dethier, Department of Geosciences, Williams College

Project Description and Goals

Fig. 1. Shaded relief and slope map of mountainous portion of Boulder Creek. Steepest slopes shaded red; shallowest slopes are blue. Study catchments include: A- Green Lakes Valley; B- Gordon Gulch and C- Betasso cutoff. Pleistocene glacial limits (white), and two existing USGS gauges are watershed shown. Boulder Falls is a knickpoint on N. Boulder Creek; similar knickzones are seen as steep-walled canyons.

The middle Boulder Creek catchment (Fig. 1) extends from the glaciated alpine zone of the Indian Peaks Wilderness Area east to the semi-arid western edge of the Great Plains. Deep, U-shaped valleys in the glaciated areas become shallower eastward through a zone of low relief and relatively low slopes, deepen into steep bedrock canyons as they pass knickzones, and flatten to lower channel slopes near the piedmont margin. Small glaciers and late-persisting snowfields dot the alpine zone, which exposes bedrock and relatively thin deposits related to the latest Pleistocene Pinedale glaciation. The thinly-forested zone of low relief exposes thick (characteristically 3 to 8 m) zones of grus, saprolite and oxidized bedrock. In the vicinity of the knickzone and downstream, slopes near channels are steep with shallow, fresh bedrock whereas more distant areas retain a deeply weathered mantle.

Project goals include: (1) education about the critical zone and methods used to characterize its development; (2) hands-on experience with field geophysical techniques and with field and laboratory methods for characterizing weathering and soils; (3) interaction with disciplinary investigators and their graduate students; and (4) contributing undergraduate topical studies to the overall critical zone project. Dethier has worked with his undergraduate students in the Boulder watershed and nearby areas on a variety of geomorphic studies for the past 9 years and with Matthias Leopold for the past 3 years.

Figure 2. View north from Niwot Ridge near the Mountain Research Station.

Niwot Ridge (Fig. 2), adjacent to the Mountain Research Station, is a long-term ecological research (LTER) site and the location for ecology and evolutionary biology research and for extensive studies about periglacial processes and landforms, snowmelt processes, and biogeochemical cycling. Keck project participants will be housed close to and will eat and recreate with students and graduate students doing research on Niwot Ridge and nearby areas. In past years these interactions have led to students helping each other on project “push” days and to some extraordinary cross-disciplinary education.

Student Projects

Students and project faculty will make measurements and collect solid or liquid samples at field sites. We will work on laboratory preparation and initial sample analysis at MSR or at the extensive analytical facilities at INSTAAR in Boulder. I expect that participants will return to their home schools with field data, initial results of some laboratory measurements and samples ready for additional analysis. Data from geophysical (after post-processing) and geochemical analyses (as necessary) will probably return sometime in the fall semester. Analysis and interpretation of field and laboratory results at the home institution will be supervised by the student’s advisor and aided by the Project Director. Some potential student projects include:

  1. Characterizing the chemistry of shallow groundwater and meltwater near late-lying snowfields in the alpine zone and/or from baseflow in deeply weathered areas.
  2. Measurement of fracture spacing, width and orientation in surface and adjacent subsurface (mine portal or drill hole) exposures. Fracture density has a strong influence on long-term rates of weathering and erosion.
  3. Mapping the depth to bedrock and the structure of the shallow subsurface using seismic refraction and ground-penetrating radar techniques.
  4. Measuring variations in soil morphology and chemistry along a slope transect from ridge crest to channel.
  5. Constructing a detailed map of surficial deposits in one of the study catchments using field measurements and LIDAR imagery.
  6. Assessing the contribution of eolian material to soils in the Green Lakes (alpine) catchment.
  7. Measuring the degree of alteration of trace minerals (allanite, sphene, Ti-magnetite, zircon) on transects from fresh rock to soil.

Field Conditions and logistics

Students will fly into Denver, Colorado on 16 July and drive up to the University of Colorado’s Mountain Research Station (http://www.colorado.edu/mrs/), where project participants will live and eat at 9500 feet at the edge of the alpine part of the Boulder Creek catchment. Housing consists of rustic cabins and meals and lunch ingredients are served in a central lodge. The Station has laboratory, lecture, library and limited computer facilities, a local wireless network and provides regular weekday transportation to and from the CU campus.
We will spend part of the first week learning about local geology and research from investigators on the NSF grant, using a lecture and field trip format, and visiting each of the field locations and nearby Rocky Mountain National Park. Students and project faculty will all work with helping to pick locations for and to set up and run geophysical lines. Students will use this regional and site-specific background and consultation with project faculty to decide on their individual research topics (see examples below); projects will depend, in part, on the logistics of the individual sites. If a drill rig is working at one of the sites, for instance, logging and analysis of the cuttings and core might provide an ideal target for individual research. It is expected that students will work as a group on setting up some measurements and individually or as pairs at other times at local sites. Communication on-site will be by GPS/radio receivers. Project participants will return home from Denver on 14 August.

Course Preparation

Important for the first year of this interdisciplinary project is a strong interest in surface and near-surface processes and in interdisciplinary science, a record of hard work and the ability to follow through. We would prefer gregarious, “can-do” students with a background in geology or physical geography and coursework in:

  • Mineralogy and/or geochemistry
  • Geomorphology or Quaternary geology or hydrology
  • Sedimentology and/or soils (valuable)
  • Structural geology, geophysics or field mapping (valuable)
  • GIS or a strong background in supporting science (useful)

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