Callahan, Russell P., Clifford S. Riebe, Sylvain Pasquet, Ken L. Ferrier, Dario Grana, Leonard S. Sklar, Nicholas J. Taylor, Brady A. Flinchum, Jorden L. Hayes, Bradley J. Carr, Peter C. Hartsough, Anthony T. O'Geen, and W. Steven Holbrook. Subsurface Weathering Revealed in Hillslope‐Integrated Porosity Distributions. Geophysical Research Letters 47, no. 15 (2020): e2020GL088322. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL088322

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Subsurface weathering has traditionally been measured using cores and boreholes to quantify vertical variations in weathered material properties. However, these measurements are typically available at only a few, potentially unrepresentative points on hillslopes. Geophysical surveys, conversely, span many more points and, as shown here, can be used to obtain a representative, site‐integrated perspective on subsurface weathering. Our approach aggregates data from multiple seismic refraction surveys into a single frequency distribution of porosity and depth for the surveyed area. We calibrated the porosities at a site where cores are coincident with seismic refraction surveys. Modeled porosities from the survey data match measurements at the core locations but reveal a frequency distribution of porosity and depth that differs markedly from the cores. Our results highlight the value of using the site‐integrated perspective obtained from the geophysical data to quantify subsurface weathering and water‐holding capacity. Plain Language Summary Weathering beneath the landscape surface breaks rock down, creating soil and opening pore space capable of storing life‐sustaining water for overlying ecosystems. Here we use existing geophysical techniques to produce a new site‐wide perspective on subsurface weathering. This approach aggregates geophysical estimates of subsurface properties needed to quantify porosity. We applied this approach across forested slopes in the Sierra Nevada, California, where previous studies measured porosity independently in cores extracted from the subsurface. The cores are vital in our calibration of the geophysical estimates of porosity. But they sample just a few potentially anomalous points on the landscape, compared to the much more representative 860‐m length of geophysical surveys at our site. Thus, our analysis highlights the limits of core‐based estimates of weathering and moreover demonstrates the value of the site‐integrated perspective obtained by aggregating geophysical data over hillslope scales.