Weathering and erosion processes are crucial to Critical Zone (CZ) evolution, landscape formation and availability of natural resources. Although many of these processes take place in the deep CZ (∼10–100 m), direct information about its architecture remain scarce. Near-surface geophysics offers a cost-effective and minimally intrusive alternative to drilling that provides information about the physical properties of the CZ. We propose a novel workflow combining seismic measurements, petrophysical modelling and geostatistical analysis to characterize the architecture of the deep CZ at the catchment scale, on the volcanic tropical island of Basse-Terre (Guadeloupe, France). With this original workflow, we are for the first time able to jointly produce maps of the water table and the weathering front across an entire catchment, by means of a single geophysical method. This integrated view of the CZ highlights complex weathering patterns that call for going beyond “simple” hillslope CZ models.

Plain Language Summary:
Infiltration of rainwater into the subsurface chemically alters and breaks down rock at depth, thus creating porous space able to store life-sustaining water for overlying ecosystems. Information about the structure and the water content of this invisible compartment is difficult to obtain. Here we use minimally invasive geophysical techniques to image this subsurface porous layer, and map the depth of the weathered zone and the water table. We applied this approach across forested slopes of Basse-Terre island (Guadeloupe, France), which is representative of volcanic tropical landscapes with strong weathering and erosion activity. We use petrophysical relationships to convert our geophysical measurements into estimates of porosity and water saturation. We then apply spatial interpolation techniques to extend our local estimates across the entire watershed. Our novel approach provides unique insights on both the physical structure and water content of the subsurface at such a scale.

Pasquet, Sylvain, Jean Marçais, Jorden L. Hayes, Peter B. Sak, Lin Ma, and Jérôme Gaillardet. Catchment-Scale Architecture of the Deep Critical Zone Revealed by Seismic Imaging. Geophysical Research Letters 49, no. 13 (2022): e2022GL098433. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL098433

© 2022. The Authors.
This is an Open Access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. https://creativecommons.org/licenses/by/4.0/

Jorden Hayes is a professor of Earth Sciences at Dickinson College.

Peter Sak is a professor of Earth Sciences at Dickinson College.

This published version is made available on Dickinson Scholar with the permission of the publisher. For more information on the published version, visit American Geophysical Union's Website. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL098433