Constraining the Effect of Climate and Rock Porosity on Weathering Extent in the Volcanic Island of Santa Cruz (Galápagos, Ecuador)

Paque, Rose;Alomia Herrera, Ilia;Dixon, Jean;Molina Verdugo, Armando;Vanacker, Veerle;et.al.
(2024) Journal of Geophysical Research: Earth Surface — (2024)

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Abstract
Few quantitative data exist on soil-landscape development in pristine volcanic ecosystems, as most of these ecosystems are prone to intensive land use and management. By working in the Galápagos Islands, a UNESCO World Heritage Site, we aim to constrain soil development over millennial timescales using empirical data. Our monitoring sites on the island of Santa Cruz cover a 10 km long NW-SE stretch with an 8-fold increase in precipitation rates and associated changes in vegetation cover. By controlling for the age and chemical composition of the basaltic parent material, we investigated the influence of precipitation rates on soil weathering and the dependence of basalt weathering on porosity of the parent material. Our results show that soils on vesicular scoria are considerably more developed than on lava flows. While volumetric changes during weathering are greater in soils developed on dense lava flows than on porous scoriae, soil depth variations are strongest on scoria material, with soil depth ranging from 12 cm to more than 500 cm. The weathering degree increases with increasing precipitation for soils developed on scoria, with clear changes in the chemical index of alteration (CIA), total reserve in bases (TRB) and chemical depletion fraction (CDF). Soils developed on lava indicate increasing weathering degree with precipitation for precipitation rates ranging between 0 and 800 mm.yr-1 and then decrease in the humid highlands. The weathering degree varies with precipitation rates, with soils almost completely depleted in major mono and divalent cations in the humid highlands.
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Paque, R., Alomia Herrera, I., Dixon, J., Molina Verdugo, A., Zehetner, F., & Vanacker, V. (2024). Constraining the Effect of Climate and Rock Porosity on Weathering Extent in the Volcanic Island of Santa Cruz (Galápagos, Ecuador). Journal of Geophysical Research: Earth Surface. Published. https://doi.org/10.1029/ 2024JF007651 (Original work published 2024)