Channel incision into landscapes underlain by bedrock creates a network of channels bordered by hillslopes. These hillslopes are typically conceived of as being mantled by a conductive, moisture-retaining soil overlying a poorly conductive bedrock. This soil moisture is exploited by plants, creating a dynamic link between atmospheric processes and evapotranspiration. Here I report the results of over thirty years of hydrologic field investigations that shows that weathering of the underlying bedrock increases porosity and conductivity, leading to significant hydrologic dynamics beneath the soil that matters to surface processes, including landsliding, solute chemistry, and moisture availability to plants. This weathered bedrock is now seen as part of a larger coevolving entity: the critical zone. The critical zone extends from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of the groundwater. Four years ago a group of Berkeley faculty, graduate students and post-docs initiated the Eel River Critical Zone Observatory (one of 9 NSF supported observatories) to explore critical zone evolution and processes. A thread through our studies is the discovery of the significance “rock moisture” which we define as exchangeable matrix water and fracture water in weathered bedrock in the unsaturated zone. Rock moisture dynamics controls runoff timing, solute chemistry evolution, vegetation dominance, and at our site is equal to about 30% of the annual rainfall, yet is missing in climate models.
About the Speaker – William E. Dietrich
William E. Dietrich became a professor in the Department of Earth and Planetary Science at UC Berkeley in 1982 after completing his PhD dissertation on river meander mechanics at the University of Washington. He is a geomorphologist who has worked on hillslope and river processes and contributed to some 250 papers. He was elected to National Academy Sciences, and is a Fellow of the American Academy of Arts and Sciences and recipient of honors including the Robert E. Horton Medal of the American Geophysical Union, the Arthur Holmes Union Medal of the European Geosciences Union, and the Martin Meyerson Berkeley Faculty Research Lecture Award.
Host: Nick Bouskill