30 Years in the Life of an Active Submarine Volcano: A Time‐Lapse Bathymetry Study of the Kick‐'em‐Jenny Volcano, Lesser Antilles

Effective monitoring is an essential part of identifying and mitigating volcanic hazards. In the submarine environment this is more difficult than onshore because observations are typically limited to land‐based seismic networks and infrequent shipboard surveys. Since the first recorded eruption in 1939, the Kick‐'em‐Jenny (KeJ) volcano, located 8 km off northern Grenada, has been the source of 13 episodes of T‐phase signals. These distinctive seismic signals, often coincident with heightened body‐wave seismicity, are interpreted as extrusive eruptions. They have occurred with a recurrence interval of around a decade, yet direct confirmation of volcanism has been rare. By conducting new bathymetric surveys in 2016 and 2017 and reprocessing 4 legacy data sets spanning 30 years we present a clearer picture of the development of KeJ through time. Processed grids with a cell size of 5 m and vertical precision on the order of 1–4 m allow us to correlate T‐phase episodes with morphological changes at the volcano's edifice. In the time‐period of observation 7.09 × 106 m3 of material has been added through constructive volcanism – yet 5 times this amount has been lost through landslides. Limited recent magma production suggests that KeJ may be susceptible to larger eruptions with longer repeat times than have occurred during the study interval, behavior more similar to sub‐aerial volcanism in the arc than previously thought. T‐phase signals at KeJ have a varied origin and are unlikely to be solely the result of extrusive submarine eruptions. Our results confirm the value of repeat swath bathymetry surveys in assessing submarine volcanic hazards. Plain Language Summary Kick‐'em‐Jenny is a submarine volcano located near Grenada in the Lesser Antilles. In 1939 a major eruption sent volcanic material up to 300 m into the air, signalling the potential growth of a new island. Seismometers have recorded further activity approximately once a decade, but these events are rarely observed directly. We therefore understand little about what is happening at the volcano ∼190 m below the sea surface. In our study we conducted bathymetric surveys of the volcano in 2016 and 2017. We combine this with 4 previous surveys of the volcano, made between 1985 and 2014, covering a number of these periods of unrest. Rather than a growing cone, we observe several small landslides from the flanks of Kick‐'em‐Jenny. In recent decades far more material has fallen away from the cone than has be