Shallow hydrothermal activity detection using high-frequency single beam echosounder in northern Weh Island, Indonesia

Hydrothermal venting is a key indicator of active submarine volcanism, visible as gas bubble streams and acoustic turbidity in shallow marine environments. Despite its significance, high-resolution acoustic imaging of vent bubble plumes in shallow volcanic coastal settings remains limited. This study aimed to apply a high-frequency single-beam echosounder (SBES) to characterize shallow-water hydrothermal venting. A field survey was conducted on March 16, 2023 at Sirui coastal area of Weh Island. Echogram analyses were used to identify four primary vent hotspots characterized by vertically coherent acoustic bubble plumes with volume backscattering strength (SV) values within −30 to −50 dB. The strongest backscatter intensities were identified close to the vent outlets. A distinct NE-SW-trending offshore bubble-vent line was identified, consistent with local fault structures and indicative of spatially coherent hydrothermal venting during the survey. Vertical backscatter profiles further reflected a progressive decrease in SV with increasing height above the seabed as a sign of bubble dispersion within the water column. The results showed the capability of a low-cost SBES to resolve fine-scale plume geometry and fault-controlled vent organization in shallow volcanic coastal environments. Future studies should integrate multi-frequency acoustics and direct bubble imaging to further constrain bubble dynamics and gas flux variability.