Abstract

I use minimally invasive shallow geophysical techniques to image the structure of the critical zone from surface to bedrock (0-25 m) throughout three small drainages within the Boulder Creek Critical Zone Observatory (BcCZO). Shallow seismic refraction (SSR) and electrical resistivity tomography (ERT) provide complementary methods for determining the physical characteristics of the shallow subsurface. Results of the SSR surveys provide a pseudo-3D network of critical zone compressional wave velocity (Vp) structure within each catchment.

The evolution of each catchment within the BcCZO contains signals of both erosion and weathering dependent upon the large-scale geomorphic processes down to the microbial weathering of mineral grains. The geophysical approach describes the arena for the small-scale processes while also providing a quantitative description of the critical zone structure at an instant in time. I use these tools to establish a three-dimensional model of critical zone architecture within three catchments with signicantly different recent and continuing geomorphic forcings: fluvial rejuvenation, long-term quiescent erosion, and glaciation. I find bedrock Vp greater than 3500 m/s, regolith Vp generally less than 700 m/s and weathered bedrock ranging from 700-3500 m/s if present.

This model will guide investigations of critical zone processes that include landscape and hydrologic modeling and will assist in expanding point measurements of chemical and biological processes to the catchment scale.

Citation

Befus, Kevin (2010): Applied geophysical characterization of the shallow subsurface: Towards quantifying recent landscape evolution and current processes in the Boulder Creek watershed, CO. Thesis, University of Colorado, Master of Science, Department of Geological Sciences.

This Paper/Book acknowledges NSF CZO grant support.