Multi‐Scale Thermal Mapping of Submarine Groundwater Discharge in Coastal Ecosystems of a Volcanic Area

Abstract Submarine groundwater discharge (SGD) in volcanic areas commonly exhibits high temperatures, concentrations of metals and CO 2 , and acidity, all of which could affect sensitive coastal ecosystems. Identifying and quantifying volcanic SGD is crucial yet challenging because the SGD might be both discrete, through fractured volcanic rock, and diffuse. At a volcanic area in the Philippines, the novel combination of satellite and drone‐based thermal infrared remote sensing, ground‐based fiber‐optic distributed temperature sensing, and in situ thermal profiling in coastal sediment identified the multi‐scale nature of SGD and quantified fluxes. We identified SGD across ∼30 km of coastline. The different approaches revealed numerous SGD signals from the intertidal zone to about a hundred meters offshore. In active seepage areas, temperatures peaked at 80°C, and Darcy fluxes were as high as 150 cm/d. SGD is therefore locally prominent and regionally important across the study area.