Uncovering Lāna’i's hidden heat: geophysical insights on the subsurface hydrothermal activity of this Hawaiian island

The Hawaiian Islands, characterized by volcanic activity and complex hydrogeological systems, encounter energy challenges due to reliance on imported fossil fuels. Therefore, exploring geothermal sources is crucial for sustainable development, given the islands' isolation. Simultaneously, understanding freshwater reservoirs is vital for sustainable water resource management. This multidisciplinary study on Lāna’i Island integrates geophysical, groundwater, and mineralogical data, unveiling insights into concealed deep hydrothermal activity and its heat source. Correlations observed in newly acquired self-potential (SP) data combined with earlier gravity and magnetotellurics (MT) data reveal the presence of a hydrothermal upflow, perhaps originating from deep magma reservoirs beneath the Pālāwai caldera. The concealed hydrothermal system emerges as a potential geothermal resource at >2 km depth, requiring further deep drilling research to confirm its presence. In addition, XRD analysis reveals varying degrees of hydrothermal alteration, indicating high temperatures during fluid-rock interactions. The alignment of surface alteration with current upflow zones suggests an active hydrothermal system persists in the caldera faults since the shield-building stage, which causes warm brackish water within the Pālāwai basin. This prompts a discussion about the possible presence of a geothermal resource. This subject has been under investigation for the past seven years as part of the Hawaii Play Fairway project. The impact of hydrothermal activity appears limited to the Pālāwai caldera and the Canyon zone, contrasting with the Munro Trail ridge area, which serves as an independent freshwater source with impounded aquifers. Understanding this convergence of geothermal investigation and freshwater reservoir analysis holds significant importance for fostering sustainability in the Hawaiian archipelago.