The Geological Origins of St. John in the US Virgin Islands

Jaw fish seen in St. John

Photo by Vlad Tchompalov on Unsplash

Paul Angelides is an engineering professional who is licensed in New York, Connecticut, and the US Virgin Islands. A part-time resident of St. John in the Virgin Islands, Paul Angelides enjoys exploring the natural aspects of the Caribbean island.

The smallest of the three islands that make up the Virgin Islands, St. John is also the least densely inhabited, with more than half of its acreage designated as national park. The rugged, densely forested island lies on a volcanic rock substrate.

St. John was formed from underwater eruptions that began 100 million years ago. Molten rock flowed out of vents in the ocean floor, which then began to rise, due to a combination of the new molten material and violent plate tectonic forces. 

Then, a period of above-sea eruptions created a foundation of solidified lava layered with sedimentary rock. Sedimentary rock is primarily limestone that is formed from marine animal and plant secretions. 

Next, stray seeds carried by ocean currents and trade winds gave the island a foothold for life. This, in turn, created a habitable island for birds, lizards, and the lone indigenous mammal, the bat. Today, the island’s volcanic origins are recognizable in the numerous rocky coves that protect the area’s extensive coral reefs and beaches.