The dual role of fracturing and elevation on the development of the weathering profile in mafic landscapes of the Andean tropics
Year: 2026
Type: article
Abstract: The Critical Zone (CZ) evolves through interactions between surface processes and the solid Earth, yet its complexity remains poorly constrained due to sparse subsurface data. Here, we analyse 18 boreholes drilled along the eastern flank of the tropical Western Cordillera to circumvent the limitations from prior studies of weathering profiles, mostly at the scale of hillslopes. The data show that deep (>48 m), multilayered weathering profiles dominate high‐elevation ridges and mid‐slopes (>1,100 m), while saprolite is absent at lower elevations. The multilayered profile consists of four layers that go from lightly (L4) to moderately (L3) weathered diabase (dark grey to light greenish grey, respectively) up to a reddish yellow to dark reddish saprolite (L1) that overlies a yellow saprolite (L2). Estimates of fracture density (P 10 ) reveal crushed zones (P 10 > 30 m −1 ) are more abundant toward the western flank of the Western Cordillera. Fracture density also increased toward the surface at shallower levels. Borehole elevation and fracturing both seem to exhibit controls on weathering profile development: at mid to low elevations, we interpret high fracture density as enhancing erosion and inhibiting saprolite formation, whereas at high elevations, fracturing combines with vegetation and moisture to promote deep weathering. Although saprolites are thick at high elevations, water table measurements show a seasonal increase in elevation of the water table, potentially enhanced by high hydraulic conductivity as estimated via packer tests (n = 5) in two boreholes. High conductivity and active percolation of meteoric water at high elevations are further confirmed by oxide/carbonate precipitation below saprolite layers. We propose that long‐term exhumation of fractured, conductive layers sustains thick weathering profiles at high elevations, whereas fracturing limits CZ development at lower sites. Notably, fractured mafic rocks develop weathering profiles comparable to granitic systems, underscoring the coupled role of lithology and structure in CZ evolution.
DOI: 10.1002/esp.70275
Institutions: Syracuse University, Weber State University
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $5,330
OpenAlex ID: W7138892759