Future of the Virgin Islands

The Virgin Islands contain a distinctive type of physical geography. The Islands were created some 100 million years ago (Belarus and Luck) due to plate tectonics and the subduction of the Caribbean plate under the North American plate. Due to its location in near the equator the Virgin Islands are tropical islands with high humidity.

The Virgin Islands are prone to rapidly changing physical geography due to impacts from the ocean. The littoral zone or coastal region of the islands is steadily shifting every day. At first the Virgin Islands were just solidified magma pushed out of the ocean. The Virgin Islands were not always sandy beaches but solid igneous rock jutting out of the ocean. Tides have taken their toll on the islands, weathering the rock and changing the formation of their sea cliffs.  There is evidence of this erosion in the sea cliff notches that from on the bottom of the sea cliffs. This encourages mass wasting as the cliff becomes less able to support the upper shelves until a storm comes and causes mass wasting. Then the process starts again with the new cliff line.

Notched Cliff on Jost Van Dyke

http://seestjohn.com/st_john_life/tag/great-thatch/

1,000 Years

In 1,000 years the littoral zones will be made up of less igneous rock and consist of larger sandy shores. The islands will become further submerged in the ocean through natural degradation due to storms and erosion.  The shore current will shift the shoreline with swash and backwash. Due to the shallow waters in that region the majority of the waves are spilling breakers, where there is minimal change in sea floor grade. The steeper the grade the larger the waves will oscillate creating a quicker physical change.

10,000 Years

As the ocean continues to impact the land form of the Virgin Islands in 10,000 years the rocky shore lines will be depleted into smooth sandy beaches. The likelihood of this happening is already evident by the formation of tombolos and lagoons on some of the islands. As waves refract around islands and formation in the ocean they meet on the opposing side pushing sand together creating a sand bridge between islands.  Many of the island shore lines are beginning to in both the British and American side of the islands has a shift in physical geography from sandy coasts to rocky sea cliffs on the leeward side.

 

Trombolo off of St. Thomas

http://www.destination360.com/caribbean/usvi/airlines-to-us-virgin-islands

100,000 Years

In 100,000 years as the wave degrade the coastal structure of the islands a new factor will affect the physical geography of the Virgin Islands, rising sea levels. The earth has always gone through cycles of ice ages as glaciers accumulate and ablate.  In the next 100,000 years the shifting of the water levels will cause the further erosion. While the cliff notches of today’s islands seem minuscule the rising water levels will allow sea tides to affect a greater area. Then when the water level decreases again the ocean floor will be emerged and turned to vegetation.

Starting as islands surrounded by cliffs the Virgin Island’s Littoral shifts will determine the future of its physical geography. From its volcanic origins the future of this tropical oasis is still undetermined. However, the ocean will naturally regulate the coast and shift the islands from cliff structures into a smooth sandy coastal system.

"GEOLOGY OF THE VIRGIN ISLANDS." BCRC Home. Web. 09 June 2010.
<http://bcrc.bio.umass.edu/vifishandwildlife/Education/AquaticEd/Coloringbook/EnvColorBook/UsedFiles/Geology.
htm>.

Luck, Tamara, and Lauren Baltrus. "Virgin Islands." Earth Science in our National Parks. Tangient LLC, 09 2010. Web. 6 Dec 2012. <https://earthscience-in-the-nationalparks.wikispaces.com/Virgin Islands>.

http://www.divelowkey.com/images/items/cloud9jost.jpg


altocumulus and stratocumulus clouds somewhere in the Virgin Islands

Up in the Air

The average level of Relative humidity in the Virgin Islands is 57% - 87%. The relative humidity is the amount of water in the air compared to how much water the air can hold. This means the Virgin Islands is a humid area.

The high levels of humidity allow the dew point to be reached much easier than in less humid climates. The dew point is when the air is fully saturated (relative humidity is 100%). It is not uncommon to see condensation in the form of morning dew or fog on the islands because the temperature drop during the night causes the amount of water the air can hold to drop which lowers the dew point.

As volcanic formed islands the Virgin Islands are mountainous. The main type of fog to form is valley fog due to the colder air draining from the tops of the mountains. Radiation fog and advection fog are the least likely types to form because it doesn’t typically get cold enough for advection fog and there is usually to much wind for radiation fog.

Another aspect affected by the dew point is clouds. As altitude increases air pressure drops allowing the dew point to drop. Clouds only form at or above the dew point. Due to the high humidity lower level clouds such as stratus (low level) and alto (middle level) tend to form.


http://weatherspark.com/averages/33722/St-Thomas-VI-US-Virgin-Islands

http://www.pr.nrcs.usda.gov/technical/soil_survey/vistsoil.htm

Soil

The Virgin Island’s soil is a complex tropical volcanic soil. The National Department of Agriculture classified it as victory soil. Victory soil forms on side slopes in volcanic areas in tropical climates and is considered an inceptisol. The O horizon is relatively shallow. The yellow and brown loamy A horizon extends about eleven inches underground before it hits the B Horizon extending nine inches further before it hits the weathered rock of the C horizon, which extends thirty inches to igneous parent rock. 
 
Victory soil of the Virgin Islands has the typical chemical properties for tropical islands. The soil has an acidic PH and a superactive CEC (Cation Exchange Capacity) meaning that plants can easily soak up nutrients due to a high amount of soil colloids that promote CEC.

The pedogenic process that seems to be occurring is Laterization. Since the soil content has a high percentage of sand and rock, the soil is very permeable allowing water to drain rapidly. This heavy drainage leads to eluviation and leaching that washes away nutrients. Plants suck up leftover nutrients that are not washed away. This leaching is what gives the soil its acidic PH, because the drainage washes away base cations (Pidwirny).

Santiago, Carmen. "VICTORY: the Representative Soil of the U.S. Virgin Islands." Natural Research Conservation Service. USDA, 12/16/2011. Web. 11 Oct 2012. <http://www.pr.nrcs.usda.gov/technical/soil_survey/vistsoil.htm>.

Pidwirny, Michael. "Soil." The Encyclopedia of Earth. Environmental Information Coalition, 07/5/2011. Web. 11 Oct 2012. <http://www.eoearth.org/article/Soil>.

Creation

To understand how the Virgin Islands were created it is necessary to understand the plate tectonics underneath them. The Virgin Islands are located along the northern edge of the Caribbean plate, where it meets the North American Plate. These plates are moving west at different speeds. North American Plate is moving at a faster rate creating a convergent boundary causing subduction (Joyce, 5). Evidence of this subduction is the Puerto Rican Trench that runs parallel to the Virgin Islands. As the North American Plate sunk below the Caribbean plate energy was released melting parts of the upper mantle into magma. This allowed it to form laccoliths that pushed land up and expose the Virgin Islands from the sea.

Evidence of the tectonic birth is all over the Virgin Islands. The location of the islands in relation to the Puerto Rican Trench is a great example of a subduction zone. The effects of subduction gave the islands some unique features. As magma cooled and solidified, erosion revealed plutons. On the island Virgin Gorda one of the main attractions is The Baths, which are batholiths or a collection of plutons.

Joyce, James. "Geologic and Tectonic Setting of the BVI." Department of Disaster Management British Virgin Islands. University of Puerto Rico Mayaguez, n.d. Web. 19 Sep 2012.

The Baths. 2012. Photograph. Golden Interest, Inc, Key West, Florida. Web. 19 Sep 2012.