The Oven of the Sea
Kavachi is one of the most active submarine volcanoes in the southwest Pacific Ocean. Located approximately 24 kilometers south of Vangunu Island, this conical seamount rises 1,200 meters from the seafloor, with its summit lying just 20 meters below the surface of the sea. The volcano is named after a sea god of the local Gatokae and Vangunu people, who also call it Rejo te Kavachi, or "Kavachi's Oven".
Since its first recorded eruption in 1939, Kavachi has erupted more than 39 times. Its activity is often powerful enough to breach the ocean's surface, ejecting steam, ash, and molten rock fragments into the air. These phreatomagmatic eruptions have formed temporary islands on at least eight separate occasions, though these small landmasses of volcanic debris are quickly eroded by wave action and disappear back beneath the waves. The water surrounding the summit is a plume of superheated, acidic water containing particulate matter, volcanic rock fragments, and sulfur.
An Unlikely Ecosystem
In January 2015, an expedition led by oceanographer Brennan Phillips arrived at Kavachi during a rare lull in volcanic activity. This quiet period allowed the research team to deploy a baited, remote deep-sea camera into the volcano's main crater. The footage revealed an unexpected community of animals living in an environment that is usually inhospitable to complex life.
Swimming through the hot, acidic water were two species of shark: the silky shark (Carcharhinus falciformis) and the scalloped hammerhead (Sphyrna lewini). The camera also recorded other fish, including bluefin trevally and snapper, as well as a sixgill stingray and gelatinous zooplankton. The discovery shows how these large animals survive in such an extreme environment. The water is hot enough to cause acid burns to human divers who have attempted to get close, and similar active submarine volcanoes elsewhere are known to create "kill zones" devoid of large animals. Scientists have observed the sharks darting in and out of the densest parts of the volcanic plume. This behavior suggests they may move in and out of the crater opportunistically rather than residing there permanently. How they sense and avoid Kavachi's frequent, violent eruptions is not yet understood.