Honeymoon Beach. Image from the National Park Service's page.
Virgin Islands National Park covers nearly two-thirds of St. John Island and its surrounding waters, part of St. Thomas Island, and nearly all of Hassel Island in the U.S. Virgin Islands. This summary draws on the National Park Service's Geodiversity Atlas, part of the Geologic Resources Inventory.
The park
Authorized on August 2, 1956, the park covers about 6,049 hectares (14,948 acres). It protects rich Caribbean marine and land ecosystems: coral reefs, seagrass beds, coves, beaches, mangrove forests, salt ponds, subtropical forests, and the largest and most intact dry tropical forests left in the Caribbean. Its tropical habitats hold more than 700 plant species, are important wintering grounds for migratory birds, and include a coral reef system supporting hundreds of aquatic species. In 1976 UNESCO designated it the first biosphere reserve representing the Lesser Antilles.
The rocks beneath it
The bedrock of St. John and St. Thomas is volcanic and sedimentary, spanning the Cretaceous through the Quaternary.
| Unit | Age | What it is |
|---|---|---|
| Lameshur Volcanic-Intrusive Complex (Water Island Formation and Careen Hill Intrusive Suite) | Cretaceous | Underlies much of the park: gabbro, basalt, andesite, keratophyre (fine-grained, silica-rich igneous rock), volcanic wacke, bedded tuff and sheeted dikes |
| Louisenhoj Formation | Cretaceous | Widespread; a mixed unit of volcaniclastic rocks, basalt, breccia, tuff, shale, chert and rare limestone beds |
| Outer Brass Limestone | Cretaceous | A thin band of calcite marble and calc-silicate beds on St. John's north coast, between the older Louisenhoj Formation and the younger Tutu Formation |
| Tutu Formation | Cretaceous | Metavolcanic and metasedimentary rocks, with the Outer Brass Limestone running from Mary Point east to Threadneedle Point |
| Dikes | Cenozoic | Biotite-hornblende tonalite, diabase, gabbro and diorite cutting the Cretaceous rocks of the north coast |
| Surface deposits | Quaternary | Loose beach deposits, beachrock (rock formed in tidal zones), swamp deposits and alluvium — the youngest units |
Protection and data
Fossils on park land are protected by the Paleontological Resources Preservation Act of 2009. The Geologic Resources Inventory has produced a digital geologic map and report for the park, and a Soil Resources Inventory has been completed; both are available on the NPS DataStore.
Sources
- National Park Service: "NPS Geodiversity Atlas—Virgin Islands National Park, Virgin Islands."
- Works it cites: Rankin (2002), on the geology of St. John; National Park Service (2016).
- The source refers once to the park's habitats as "within SARI," apparently a slip for Virgin Islands National Park.
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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