Climatic and lithological control on soil development in volcanic islands. Case study: Santa Cruz Island, Galápagos Archipelago by Rose Paque

Soils play a crucial role in sustaining life on Earth. However, these vital resources are threatened, leading to significant degradation. This thesis aims to deepen our understanding of soil formation, weathering, and erosion processes over timescales ranging from 10³ to 10⁵ years, focusing on soils derived from basaltic rocks in a pristine natural environment: Santa Cruz Island, in the Galápagos.

Main results show that parent material porosity and precipitation strongly influence chemical weathering processes. Porosity-enhanced weathering is particularly important in humid precipitation regimes where soils developed on porous scoriae developed profiles that are ~10-fold thicker and have 10-fold higher mass losses due to weathering compared to soils developed on lava flows.

Meteoric cosmogenic 10-beryllium (10Bem) is used as a tracer of soil erosion. In this study we investigated how precipitation patterns affect the deposition of 10Bem. On Santa Cruz Island, the inversion layer formed during the cool season amplifies 10Bem deposition in the highlands, whereas intense convective precipitation during the warm season dilutes 10Bem concentrations in rainwater. Local quantification of 10Bem depositional fluxes enabled the calculation of erosion rates along the climatic gradient, ranging from 5 to 78 mm/kyr.

This thesis underscores the interplay between rock porosity and precipitation in basaltic soil development. The findings contribute to a more nuanced understanding of tropical basaltic soil processes.