Source to Sink:  Weathering of volcanic rocks and their influence on soil and water chemistry in central Oregon

What: This project is based in the High Cascades of central Oregon and the Deschutes Basin and integrates studies of bedrock, soil, and water chemistry.  The project will focus on physical and chemical weathering of volcanic rocks and factors that can influence the weathering processes, including climate and vegetation.  We will attempt to trace geochemical signatures of the bedrock as it breaks down into soil.  We will also study the water geochemistry to assess the effects of the bedrock and soil composition on the fluxes from the watershed.

When: June 22 – July 20

Where: Deschutes Basin, central Oregon and Union College, NY

Who: 6 students.  Holli Frey, Assistant Professor, Union College and Kathryn Szramek, Visiting Assistant Professor, Washington & Lee University

Project Description and Goals

Chemical and physical eathering of rock into regolith or soil is an important process that links the geosphere with the biosphere, atmosphere, and hydrosphere. The rates and mechanisms of soil formation depend on how these spheres interact and contribute to many important processes such as nutrient and carbon cycling.  Integrating the rates of chemical and physical changes to bedrock over long time scales is one component of understanding the evolution of landscapes.
Scientific goals of the project include: (1) increased understanding of the critical zone, the link between the geosphere, biosphere, atmosphere and hydrosphere; (2) expanding the data set of volcanic weathering into basaltic-andesite to andesite volcanic terrains, information which has been dominated by basaltic weathering studies; (3) to examine the geochemical fluxes out from these volcanic terrains; and (4) creating GIS maps to allow for an easily interactive database in which to collect the geochemical results.

Student Projects

We have identified a series of student projects that will collectively contribute to our understanding of how volcanic rocks weather to regolith/soil and affect the geochemistry of surrounding watersheds.  The proposed student projects are subject to individual interest and expertise, but because of the interdisciplinary nature of the project, it is necessary to have at least one student committed to each subgroup.

  • Bedrock petrology and geochemistry (1-2 students). In the field, students will map and sample bedrock material (basalt-andesite) and/or tephra (dacite-rhyolite) that has experienced different degrees of weathering.  The samples will be analyzed for major/trace elements (Ca, Mg, Na, K, Fe, Mn, Al, Zn, Ti, etc.) at Union College or the student’s home institution.  In thin-section, the breakdown and alteration of minerals will be characterized with a polarizing microscope and scanning electron microscope.  If time permits, students may also sample similar lithologies of different ages (determined in previous studies of the region) to see how that parameter affects weathering rates and decomposition.
  • Soil characterization (2-3 students). Soil sampling sites will be chosen to capture a range of conditions, including bedrock types and climate (mean annual temperature and precipitation).  Climate signals will be investigated by sampling at different elevations within the field region.  Once the sites are chosen, students will dig a few main pits to do complete soil analysis (see below) and auger holes to add supplementary chemical data.Students will characterize each main soil profile in the field by examining the soil horizons, color, texture, and organic matter, among other properties.Samples will be collected at each change in soil horizon and regular intervals within the horizons (10 cm) to determine chemical and mineralogical changes with depth in the profile.  Samples will be characterized with X-ray diffraction characterization of clay species, ICP-OES and ICP-MS analyses for major/trace elements (Ca, Mg, Na, K, Fe, Mn, Al, Zn, Ti, etc.).  Total organic carbon will be determined via loss on combustion.  Particle-size distribution will be assessed with a grain-size coulter.
  • Water geochemistry (2-3 students). Geochemical fluxes from the study area will be evaluated via river geochemistry and overall discharge from the region.  The region has many streams and a few lakes as well as springs that are available to sample.  Sample sites will be chosen to coincide with the soil and bedrock locations as well as any United States Geological Survey (USGS) stream gauge locations within the Deschutes Basin.  There are multiple gauged sites along the Deschutes River, which will provide a record of the long-term discharge characteristics of the area.  In the field students will measure temperature, conductivity, dissolved oxygen, and pH.  Samples will be collected for total bicarbonate (HCO3-) alkalinity, and for major and minor elements analysis via ion chromatograph and ICP-MS (Ca, Mg, Na, K, Sr, Fe, Al, Mn, Li, Si, Cl, SO4, P, and NO, etc).  Depending on the available funds and interest, samples for isotopic analysis may also be collected.  In addition to the chemical sampling, students will take discharge measurements at selected sampling sites in order to determine the geochemical fluxes from the region during the study.
  • GIS (1 student). To better understand the relationship between the rocks, soil, and water chemistry, all of the data needs to be integrated.  For a student proficient at GIS, several models could be made.

Field Conditions

The fieldwork will be based in the Deschutes Basin of central Oregon for 2.5 weeks.  We will be tent camping at LaPine State Park, with shower/toilet, laundry facilities and electrical outlets located in the campground.  Meals will be prepared by the group over campstoves.  The majority of the sampling sites will all be within 1.5 hours of the campground.  Extensive hiking may be required for some projects to sample springs or obtain soil transects not accessible via the field vehicles.  The labwork will be based at Union College for the last 1.5 weeks of the project.  Students will reside in Union College dormitories and have access to all facilities on campus.

During this portion of the project, students will prepare samples for analysis and begin preliminary labwork with Union’s facilities (ICP-MS, ion chromatograph, scanning electron microscope, grain size coulter, X-ray diffractometer).

Course Preparation

Students should have completed their junior year and should have taken one or more of the following courses: mineralogy, petrology, geochemistry, geomorphology, soil science, or GIS.  Previous field mapping and lab experience is also highly desirable.