Submarine Volcanic Dome Growth at Vailulu’u Seamount, American Samoa

Document Type

Presentation

Date of Original Version

3-27-2026

Abstract

Vailulu’u seamount is the youngest volcano along the Samoan hotspot track. In 1995, earthquake swarms were detected near Vailulu’u, ranging in magnitude from 4.2 to 4.9. A seabeam survey over Vailulu’u in the same year did not reveal any changes to the seafloor indicative of a recent eruption. However, a subsequent bathymetric survey in 2005 revealed the growth of a new volcanic dome, Nafanua. Repeated surveys of Vailulu’u tracked Nafanua’s growth over two decades to a height of ~300 meters above the seafloor. In 2024, a NOAA Ocean Exploration Cooperative Institute cruise aboard the E/V Nautilus surveyed Nafanua and collected high resolution bathymetric data (1 - 2 meter) with AUV Sentry, and high definition video footage with ROV Hercules. These surveys indicated that no significant new eruption activity had occurred at the Nafanua dome since 2017 and revealed new details of the volcanic structure. Rock samples were collected across the volcanic complex at each prominent peak of`Nafanua. Volcanic glass was analyzed for major element geochemistry via electron microprobe and textural characteristics were documented via scanning electron microscopy. The new high resolution and previous shipboard multibeam data was cleaned and gridded in Qimera, and ROV footage was annotated to mark significant geologic features. These data were used to investigate the physical and petrologic processes that led to this protracted submarine eruption and associated volcanic dome emplacement. They also show how the eruption evolved over 15 years of activity and the changing lava rheology. Additionally, the same geological transects conducted using the ROV provided evidence for extensive and persistent low-temperature hydrothermal flow even in the absence of recent volcanism. These results help inform the growth and evolution of the Samoan archipelago and ocean island hotspot systems globally, and will provide critical context for ongoing ecological studies of the area.

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