Kick 'em Jenny rises more than 1,300 meters from the seafloor to a summit currently sitting about 185 meters beneath the surface, according to the Global Volcanism Program. It is the southernmost active volcano in the Lesser Antilles volcanic arc, formed where the South American tectonic plate dives beneath the Caribbean plate - the same subduction zone that built Martinique's Mount Pelee and Montserrat's Soufriere Hills. But unlike its above-water neighbors, Kick 'em Jenny does its work in darkness and pressure, invisible to everyone except the seismographs monitored by the University of the West Indies Seismic Research Centre in Trinidad and Tobago. A submersible survey in 2003 found a crater with active fumaroles, releasing both cold and hot gas bubbles into the water column. The volcano is growing. Whether it will ever break the surface again is a question the ocean has not yet answered.

The 1939 eruption remains the largest on record. On July 23 and 24, the volcano breached the surface, hurling a cloud of steam and volcanic debris into the sky and generating a series of tsunamis roughly two meters high by the time they reached the coastlines of northern Grenada and the southern Grenadines. The waves were felt as far as the west coast of Barbados, where a sudden swell washed over a coastal road at Paynes Bay. A large number of people in northern Grenada witnessed the eruption cloud, but nobody knew what they were looking at - the volcano had never been documented before. Since 1939, at least fourteen eruptions have been recorded through 2017, the most recent on April 29 of that year. None has matched the violence of the first, and most were detected only by seismographs or heard as a deep underwater rumble by nearby fishermen. In 2015, elevated seismicity and an hourlong explosion event briefly raised the alert level to orange before activity subsided.

The most unsettling thing about Kick 'em Jenny is not the eruptions - it is the bubbles. Volcanic gases venting from the seafloor reduce the density of the water above the volcano. A ship floating over a sudden gas release could, in theory, lose buoyancy and sink without warning in otherwise calm seas. This hazard is real enough that a Maritime Exclusion Zone surrounds the volcano, monitored by the Seismic Research Centre. Under normal conditions the zone extends 1.5 kilometers from the volcano's center. During periods of heightened seismic activity, it expands to five kilometers. The zone sits directly on the shipping route from St. Vincent to Grenada, marked on marine charts with the kind of notation that makes captains pay attention. In 2017, researchers aboard the RRS James Cook, led by marine geophysicist Jenny Collier, observed ongoing submarine activity - a reminder that the volcano is not sleeping, merely quiet.

What makes Kick 'em Jenny compelling is what it represents: the Caribbean's geological youth. These islands are not ancient and stable. They are the tips of a volcanic arc still being built by the collision of tectonic plates, and the process is not finished. Grenada itself was born from volcanic activity - St. George's harbor is a flooded crater. Kick 'em Jenny is simply the newest expression of the same forces, a mountain under construction that has not yet earned its place above the waves. For now it announces itself only through tremors, gas bubbles, and the occasional rumble that fishermen hear through their hulls. From the air, the strait between Grenada and Ronde Island looks like any other stretch of Caribbean blue - warm, inviting, deceptively calm. Eight kilometers to the west, Ronde Island sits quietly. Eight kilometers to the south, Grenada's green hills rise from the water. And directly below, hidden in the dark, the Earth is still building.