Geography Distinguished Lecturer - William Dietrich

February 26, 2015

Title: The soil is not enough:   going inside hillslopes to understand moisture return to the atmosphere, and controls on tree distribution, stream ecosystems, and landscape evolution

  • Lecturer: William E. Dietrich, Department of Earth and Planetary Science, University of California, Berkeley
  • Date: Feb. 26th, 2015
  • Time: 3:30-5:00 pm
  • Location: IRMACS Theatre, SFU

Abstract: In hilly landscapes mantled by soil it is commonly assumed that the soil-bedrock boundary defines the depth to moisture availability to plants and sets a permeability contrast that redirects lateral subsurface flow to channels, thus controlling pore pressure buildup that drives slope instability and chemical evolution of waters.   Weathering of the bedrock, however, typically increases its permeability, causing infiltrating waters to pass into the weathered bedrock, and eventually to perch on the weathered- fresh bedrock boundary at depth and travel laterally to streams.  Little is known about this deeper region in the hillslope, i.e. the lower part of the “critical zone”.   The depth to fresh bedrock boundary may be predicted from a coupled model of surface erosion and groundwater drainage of the fresh bedrock.  Above the fresh bedrock in the weathered zone, seasonally dynamic “rock moisture” storage develops that is used by vegetation and returned to the atmosphere.  This process is missing in land surface climate models. Tree distribution may in part be controlled by access and use of rock moisture.  Rock moisture also vertically drains and recharges the perched groundwater.  Exiting water from this zone can drive landslides and control solute fluxes.  In seasonally dry environments, slow drainage of this critical zone to adjacent channels sustains base flow and thus supports the river ecosystem.  Exploration of the physical characteristics and processes in this critical zone inside hillslopes is a frontier area of earth surface processes research.

Bio: Bill Dietrich is one of the world’s leading Geomorphologists.  He holds a BA from Occidental College and an MSc and PhD from the University of Washington, all in Geology.  He has been a Professor of Earth and Planetary Sciences and Geography at the University of California, Berkeley since 1981.  He is a Fellow of the National Academy of Sciences, the American Academy of Arts and Sciences, the American Geophysical Union (AGU) and the Geological Society of America.  Among the major honours he has received is the Robert E. Horton Medal  from AGU in 2009 and the Arthur Holmes Union Medal from the European Geosciences Union in 2011.  Bill has authored more than 230 peer-reviewed papers and book chapters.  His career began with examination of flow and sediment transport in river bends and exploration of hillslope hydrology.  His work has since expanded to virtually every major research question related to the Earth’s surface, including the role of life in the topographic evolution of Earth, the impacts of land use activities and climate on landscape evolution, and exploration of the Martian landscape.  He is currently a member of the team that guides the work of NASA’s Mars rovers.  His recent work focuses on the ‘critical zone’, the heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organisms regulate natural habitat and determine the availability of life-sustaining resources.  Since 1983, Bill has hosted and organized the Gilbert Club, an annual gathering to discuss geomorphology following the Fall AGU meeting, which has fostered the major intellectual growth and expansion of Geomorphology over the past 30 years.