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Natural Resources (Terrestrial) |
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Geology 
Photo: S. Gore
The wide arc of Caribbean Islands is located on the edge of the Caribbean plate underneath which the American oceanic plates are sinking. This movement resulted in volcanic activity which occurred over 50 – 100 million years ago resulting in the formation of the Caribbean Islands. Most rocks in the Virgin Islands are more than 70 million years old, while islands further south still have active volcanoes.
The Virgin Islands and Puerto Rico rest on a submerged platform presently 100 feet deep. The Anegada Trench, a deep fracture in the Caribbean plate reaches a deep of 2.3 miles and separates of the island of St. Croix in the US Virgins from the main platform. It is approximated that between 10 – 20,000 years ago as water was locked up at the poles the sea level was 300 feet lower and during this time the Virgin Islands/Puerto Rico platform was above sea level and it would have been possible to walk between all the islands with the exception of St. Croix. The Coral Island 
Anegada rests on the northeastern edge of the same submerged platform as the other islands of the Virgin Islands and Puerto Rico, but its formation is not volcanic in origin. It is made of limestone, and is estimated to be less than one million years old. Sediment produced by mollusks and corals were swept into sandbanks and compressed to form limestone, a process which took thousands of years.
Rocks 
Rocks on these islands fall into two major categories, volcanic and sedimentary. Rock types typically found here which are of volcanic origin include
andesite - comprised of a fine grained material made up of silica, iron, calcium and magnesium; basalt - the most abundant of the volcanic rocks, these are mostly black or very dark grey in colour, some are also magnetic due to the presence of the mineral magnetite; tuffs – formed from compressed layers of volcanic ash which was blown into the atmosphere, often tuffs contain other rock fragments; granite – formed when molten material seeped from below the crust mixed with existing rocks and cooled slowly allowing for the formation of crystals. These rocks are typically much harder than surrounding rocks and tend to remain standing when softer rocks have been eroded away. Striking examples of granite can be seen in the boulders at the Baths on Virgin Gorda. Vegetation 
Vegetation type in the BVI is largely influenced by rainfall. The heaviest rainfall is typically recorded between August and November although this cannont be relied on as there are irregularities from year to year. The shape of the islands have a significant influence on the where rainfall will occur. Most rainfall occurs higher up and behind the hills, Beef Island and the south eastern side of Tortola receive less rain than the north-western side. The smaller islands consistently receive less rainfall than Tortola due to lower hills.
The rainfall pattern results in different types of vegetation being found at different heights. Vegetation types in the Virgin Islands can be categorized as follows; Littoral Zone 
Found behind beaches and rocky shores, plants in this zone must be salt tolerant due to their close proximity to the sea. Salt and constant wind from the sea dry out the soil and with the addition of the lack of rain, conditions are very dry. Much of the plants under these conditions have adapted to store water collected during rains for use during the dry season. Succulents such as Sea Purslane (Sesuvium portulacastrum) are good examples. Other plants typical of this zone include Seagrape (Coccoloba uvifera) and Manchineel (Hippomane mancinella). Coastal Scrub 
This type of vegetation is located at low elevations, yet beyond the littoral zone. The soil in this area is typically very thin, exposed to strong winds and little moisture, thus limiting the height of the vegetation. Thorny shrubs, such as the Century Plant or Cauretaw (Agave missionum) and cacti such as the Didle Doe or Pipe Organ cactus (Cephalocereus royenii) are typical species. Another typical species of the coastal scrub region is the Frangipani (Plumeria alba) which is one of the most attractive of the coastal trees with its whorls of long pointed dark green leaves and fragrant white flowers. Dry Woodland 
As elevation increases, coastal scrub gradually transitions into dry woodland. Characteristic species include the Turpentine tree (Burseria simaruba) and Mampoo or Loblolly/Blollee tree (Pisonia subcordata). Moist Forest 
Found at higher slopes of the larger islands, the best examples are found at Sage Mountain and Gorda Peak, both of which have been designated National Park areas. These areas possess the best diversity of tree species remaining in all of the Virgin Islands. Trees such as the Bulletwood ( ) and the BVI’s national tree, the White Cedar (Tabebuia heterophylla) grow to significant heights. Most trees in are evergreen.
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Monitoring Information