Geophysics in the Critical Zone

The "Critical Zone" can be defined as the zone where life and rocks interact -- the layer of air, vegetation, soil, water, and rock that bounds the top of the canopy to the base of groundwater.  What's fascinating about the CZ is the diversity of scientific disciplines that intersect there -- geology, biology, hydrology, chemistry, geomorphology, ecology, atmospheric science, and soil science.

 The National Science Foundation is funding a number of Critical Zone Observatories (CZO's) that span a range of climatic, geological, and ecological variables.  My group has been working with Dr. Cliff Riebe, a geomorphologist/geochemist in our department, at the Southern Sierra Nevada CZO.

A key question in surface processes is:  what controls the thickness of the regolith (weathering zone) above bedrock?  This question sounds deceptively simple, but, perhaps surprisingly, there is no unifying theory that encapsulates the geological, geomorphological, biological and chemical processes that control regolith development and thickness.  Part of the difficulty is a paucity of data about weathering zone thickness -- since often the regolith is too thick to trench.

That's where geophysics comes in.  Using near-surface geophysical methods like seismic refraction, GPR, and resistivity, we can discern the physical properties of the subsurface.  We've been doing this in the SSCZO, and the results show a deeper weathering zone (20-30 m) than previously thought. 


In the photo above, we're conducting a "barenaked granite" refraction survey, with geophones plastered onto a granite outcrop.

Geophysics in the CZO's is likely to become an increasing effort in our group.  Right now Jorden Hayes is working on this topic as part of her PhD dissertation.


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