Kavachi belongs to the world of submarine volcanoes, which mostly do their erupting out of sight and occasionally form islands above the surface of the water. These islands have reached more than 500 feet in length. But submarine volcanoes can become just as large and violent. For instance, the undersea Loihi volcano in the Hawaiian Islands may be invisible at sea level, but it towers almost 10,000 feet above the ocean floor. That's taller than Mount St. Helens.
Some submarine volcanoes form where Earth's tectonic plates meet.
This results in eruptions along rifts in the ocean floor. Since these eruptions are surrounded by water, they behave differently than their land-based relatives. The lava that pours out onto the sea floor cools rapidly in the water. As a result it tends to shatter into sand and debris that begin to pile up in a sloping pattern. Unlike land-based lava flows, which bind to the mountains from which they come, submarine volcanoes build themselves up particle by particle.