Chemical weathering produces soils and the necessary nutrients for ecosystems; additionally, it regulates the climate at geologic timescales. Therefore, weathering is a fundamental process for the Earth’s living layer: the Critical Zone. Despite the limited areal extent of volcanic regions, weathering of volcanic rocks contributes to these processes disproportionally due to their high reactivity. The Island of Hawaii constitutes a natural laboratory to evaluate chemical weathering reactions in volcanic terrains. In this dissertation, I contribute to the understanding of chemical reactions driving intense and fast weathering of Hawaiian basalts using a reactive transport model that incorporates organic acids and soil respiration. I have also investigated the chemical processes involved in incipient weathering of Hawaiian basalts by analyzing the distribution of major and trace elements in spheroidal saprolite samples. Further on, I provide insights into the effects of weathering on runoff-to-groundwater partitioning and the landscape evolution of the Island of Hawaii by modeling watershed-scale hydrologic parameters on catchments affected by different degrees of weathering. Finally, I developed an equilibrium fractionation model for Ge and Si in kaolinite that can be implemented on different geochemical models of silicate weathering.