Reconnaissance of ground-water quality in the U.S. Virgin Islands, July 1984
No abstract available.
Virgin Islands↗
Geology topics
Research about Virgin Islands
Source-linked reports with geographic coverage including Virgin Islands.
Floods of April 18, 1983 on St. Thomas and St. John, U.S. Virgin Islands
The U.S. Virgin Islands of St. Thomas and St. John experienced the most intense rainfall event in recorded history on April 18, 1983. Rainfall intensities of 2.5 inches per hour, and more than 16 inches in 18 hours were recorded. Almost instantaneous runoff caused widespread flooding near the coastlines of both islands. Parts of Charlotte Amalie in St. Thomas were inundated with four feet or more of mud and flood water. Harry S. Truman Airport was flooded for two days with two to three feet of ponded water. On St. John, rural areas near Guinea Guy, Fish Bay, and Coral Bay were flooded.
Virgin Islands↗
delta18O variations in the Halimeda of Virgin Islands sands: evidence of cool water in the northeast Caribbean, late Holocene
Halimeda segments from carbonate sands on the Virgin Islands platform have delta 18 O versus PDB isotopic values ranging from -0.3% to -1.3% (x = -0.9%). Modern Halimeda segments from the same area have a measured delta 18 O ranging from -2.0% to -2.5% PDB (x = -2.15%), and the carbonate skeleton appears to have formed in isotopic equilibrium with the oceanic waters on the platform. Biologic and geochemical data indicate that the sand deposits have accumulated under physical and chemical conditions similar to the modern shelf environment. 14 C data suggest that the sand was deposited over an approximate 5800-year span, centering about 4000 years B.P. The average isotopic difference of 1.25% between the Holocene and modern carbonate indicates that the late Holocene Halimeda lived in waters approximately 4 degrees cooler than the present.
Virgin Islands↗
Sedimentology of Southwestern Roads region, U.S. Virgin Islands: origin and rate of sediment accumulation
Sand deposits on southern insular shelf of St. Thomas, U.S. Virgin Islands, were investigated to determine their origin, environmental processes and accumulation rates. Sea-floor samples show that the sand has been derived (in situ) mainly from calcareous algae and molluscs. Zonation of the dominant sand producers is related to the present environmental setting; water depth has the greatest influence. Carbon-14 data (bulk sample) of cores indicate accumulation rates of slightly less than 1 mm/year for the last 5,000 years. Faunal studies show that the climate has remained constant over the past 5,000 years. The only changes in environmental conditions appear to have been an increase in water depth, changes in the patterns of water movement, and an increase in water temperature.
Virgin Islands↗
Organochlorine residues and shell characteristics of roseate tern eggs, 1981
Roseate Terns ( Sterna dougallii ) breed in two areas in the Western Hemisphere: in northeastern North America between Long Island, New York, and Nova Scotia, and around the Caribbean Sea from the Florida Keys and the Bahamas to the Netherlands Lesser Antilles (Bent 1921, Bond 1956, Nisbet 1980). Both populations are small, and concern recently has been expressed about their status (Nisbet 1980, Buckley and Buckley 1981). The northeastern population has decreased from a peak of about 8500 pairs in the 1940s to between 2500 and 3000 pairs in 1978-1982, and has become largely concentrated into 4 colonies (Nisbet 1980). The Caribbean population has been affected by egg collecting and other forms of human disturbance in its main stronghold in the U.S. Virgin Islands (U.S. Virgin Islands Bureau of Fish and Wildlife 1976-1979, Norton 1980, 1981). One factor which may have affected the northeastern population is chemical pollution. Hays and Risebrough (1972) reported high levels of polychlorinated biphenyls (PCBs) and l,l-dichloro-2,2-bis(p-chloro phenyl) ethylene (DDE) in 3 Roseate Tern chicks found with congenital abnormalities at Great Gull Island, New York, in 1970. High levels of PCBs were also found in chicks found dead at Bird Island, Massachusetts, in 1970 (Nisbet 1981). A close relative, the Common Tern ( S. hirundo ), is relatively sensitive to the effects of DDE; elevated residues of DDE in eggs are associated with eggshell-thinning (Switzer et al. 1973), reduction in the porosity of eggshells, and embryonic mortality (Fox 1976). The present paper reports the results of a survey of organochlorine residues in Roseate Terns in 1981. The main objectives of the survey were to determine the levels of organochlorine contamination in eggs of the Roseate Tern in its major colonies and to investigate whether changes in eggshell characteristics similar to those reported by Fox (1976) may have occurred in this species. A secondary objective was to determine geographic patterns of organochlorine contamination within the northeastern U.S. population of Roseate Terns and to compare them with patterns observed in Common Terns
Connecticut, Massachusetts, New York↗
Test well sites and preliminary evaluation of ground-water potential in Tortola, British Virgin Islands
Moderate supplies of potable ground water are believed to be available in the Roadtown and Paraquita Bay areas, and small, possibly brackish supplies in the Long Look and West End areas of Tortola. Two water bearing units of the same hydrologic system have the potential of yielding water to wells: 1) alluvial deposits, possibly as thick as 60 feet and locally containing beds and lenses of gravel 1 to 5 feet thick; and 2) fractured and jointed bedrock, especially where it is overlain by alluvium. The most productive ground-water areas are expected to be the lower reaches of the larger valleys. Here the alluvial deposits are thickest and the valleys often follow the trace of fault or fracture systems in the bedrock. A potential yield of 195,000 gpd (U.S. gallons per day) is estimated to be available in the Road Bay area, 55,000 gpd in the Long Look area, and 8,000 gpd in the West End area. Sites are suggested for test and monitoring wells in the lower courses of six of the valleys on the south coast.
Virgin Islands↗
Water resources of the Virgin Islands, a preliminary appraisal, 1963
Rainfall in the Virgin Islands averages about 44 inches per year, yet fresh water is in short supply, and the general impression of the islands is one of dryness. Land slopes are steep and runoff from rainstorms flows rapidly to the sea in the numerous, short, steep stream courses. During most dry seasons only a few streams maintain flow along any part of their course. Guinea Gut, the only stream in St. John known to have had continual flow during the first half of 1963, had a minimum flow of 3,500 gallons per day (gpd). The flow of Turpentine Run, the largest stream in St. Thomas, dropped to 15,000 gpd during the same period, and the flow of River Gut, the largest stream in St. Croix, dropped to about 70,000 gpd. In past years the flow of the streams has been less at times; in fact, Turpentine Run reportedly did not flow during part of 1923 and probably it has been dry at times since then. The streams thus are not reliable sources of large water supplies unless storage is provided. The building of reservoirs has been discouraged by several factors including the apparent scarcity of good sites, the lack of appreciable stream flow most of the time, and the large amount of sediment carried by the streams during floods.
Virgin Islands↗
Geology and hydrology of dam sites on the island of St. Croix, Virgin Islands
The Virgin Islands Corporation plans to build a series of small earth dams along some of the streams on the island of St. Croix, and field studies involving the selection and hydrology of possible sites was carried on by the Geological Survey during the months of August and September 1951. The island of St. Croix is the largest of the three principal islands of the Virgin. Islands group owned by the United States. It is about 21 miles long and 6 miles wide near the center and has an area of about 84 square miles. The northwestern part of the island contains mountains that reach a maximum altitude of 1,165 feet; the eastern half of the island is submountainous, containing some hills 600 to 800 feet in altitude. A coastal lowland area containing a few east-west trending marl and limestone hills characterizes the southwestern part of the island. The streams in the east half of the island and along the northwest coast are relatively short and are dry during most of the year. The streams draining the mountains from the south cross the coastal lowland in narrow and shallow ditches. The southeastward drainage from the eastern part of the mountainous area is diverted by Salt River and enters the sea on the north coast of the island. In the headwaters of some streams there is a small flow of water during most of the year that disappears below the surface upstream from or near the foot of the mountains. During most of the year the streams are essentially dry, flowing only after periods of heavy rainfall. In the coastal lowland near Bethlehem the average annual rainfall is about 46 inches. The east end of the island is relatively dry and the precipitation is estimated to be approximately 20 inches annually; the northwestern end of the island receives the most rainfall, probably more than 50 inches annually. Records show that from 1861 to 1876 there was deficient rainfall and the accumulated departure below normal was about 56 inches (fig. 2). From 1876 to 1920 there were numerous years of above -normal precipitation and the departure curve rose nearly 100 inches, to more than 40 inches above normal. From 1936 to 1950 there has been a more or less continuous decline in rainfall, amounting to a net deficiency of 72 inches, or from 44 inches above to 28 inches below normal. These changes in rainfall have a direct effect on the volume of stream flow an island. There are two general rock types on the island. The Mount Eagle volcanics and the intruded diorite are hard, dense crystalline rocks; the rock's underlying the coastal lowland and belt of hills between Salt River and Christiansted are sedimentary rocks, such as marl, limestone, sand, gravel, and clay. The permeability of the crystalline rocks and of the gray clay and basal conglomerate of the Jealousy formation is low and they are water bearing in few places. The Kingshill formation is composed of light-gray clay and light-yellow marl and included beds of limestone. In places the limestone contains solutional openings that yield water to wells. The alluvial sand, gravel, and clay that unconformably overlie the Kingshill marl include permeable beds that yield relatively large quantities of water to wells in a few places. It is evident from the small stream flow that by far the greatest part of the 46-inch average annual precipitation on the island is returned to the atmosphere through evaporation and transpiration. There are no records of stream flaw or ground-water flow from the drainage basins, but it is estimated that in some years the amount of water lost through evaporation and transpiration may be more than 90 percent of the total water available. It is proposed that a program be started and continued to collect and evaluate data on the hydrology of the island. The purpose of the dam-building program is to retain on the land a part of the water that formerly flowed to the sea and was of no beneficial use. Owing to the lack of hydrologic data, the maximum number of dams needed is not known; consequently, practically all possible sites on publicly owned land and sites that would benefit those lands were studied. Thus, 3 sites were selected in the valley near Little Grange that is a source of supply to the public-supply well field of Frederiksted; 19 sites were selected on or near property owned by the Virgin Islands Corporation; and 4 sites were selected along the Salt River above the public-supply well field of Christiansted. During most of the year the water table is at or below the beds of the streams; consequently, if permeable rocks underlie a pond or dam it is possible that there may be leakage from the pond to the water table. In general, leakage from dam sites underlain by crystalline rocks of the fount Eagle volcanics or clay of the Kingshill marl will be negligible, but leakage from sites underlain by limestone in the Kingshill marl or sand and gravel of the alluvium may be great. Potential leakage at each site selected is discussed.
Virgin Islands↗
Additional water development on St. Thomas, Virgin Islands, with an addendum on St. Croix
No abstract available.
Virgin Islands↗