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S. K. Izuka

Publications and source records attributed to S. K. Izuka.

12 recordsLinked to original sources
USGS2008

Evidence of Late Pliocene-Early Pleistocene marine environments in the deep subsurface of the Lihue Basin, Kauai, Hawaii

Cuttings recovered from two deep exploratory wells in the Lihue Basin, Kauai, Hawaii, include fossiliferous marine deposits that offer an uncommon opportunity to study paleoenvironments from the deep subsurface in Hawaii and interpret the paleogeography and geologic history of Kauai. These deposits indicate that two marine incursions gave rise to protected shallow-water, low-energy embayments in the southern part of the Lihue Basin in the late Pliocene-early Pleistocene. During the first marine incursion, the embayment was initially zoned, with a variable-salinity environment nearshore and a normal-marine reef environment offshore. The offshore reef environment eventually evolved to a nearshore, variable-salinity environment as the outer part of the embayment shallowed. During the second marine incursion, the embayment had normal-marine to hypersaline conditions, which constitute a significant departure from the variable-salinity environment present during the first marine incursion. Large streams draining the southern Lihue Basin are a likely source of the freshwater that caused the salinity fluctuations evident in the fossils from the first marine incursion. Subsequent volcanic eruptions produced lava flows that buried the embayment and probably diverted much of the stream flow in the southern Lihue Basin northward, to its present point of discharge north of Kalepa Ridge. As a result, the embayment that formed during the second marine incursion received less freshwater, and a normal-marine to hypersaline environment developed. The shallow-water marine deposits, currently buried between 86 m and 185 m below present sea level, have implications for regional tectonics and global eustasy. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Palaios↗
USGS2003

A thick lens of fresh groundwater in the southern Lihue Basin, Kauai, Hawaii, USA

A thick lens of fresh groundwater exists in a large region of low permeability in the southern Lihue Basin, Kauai, Hawaii, USA. The conventional conceptual model for groundwater occurrence in Hawaii and other shield-volcano islands does not account for such a thick freshwater lens. In the conventional conceptual model, the lava-flow accumulations of which most shield volcanoes are built form large regions of relatively high permeability and thin freshwater lenses. In the southern Lihue Basin, basin-filling lavas and sediments form a large region of low regional hydraulic conductivity, which, in the moist climate of the basin, is saturated nearly to the land surface and water tables are hundreds of meters above sea level within a few kilometers from the coast. Such high water levels in shield-volcano islands were previously thought to exist only under perched or dike-impounded conditions, but in the southern Lihue Basin, high water levels exist in an apparently dike-free, fully saturated aquifer. A new conceptual model of groundwater occurrence in shield-volcano islands is needed to explain conditions in the southern Lihue Basin.

Hydrogeology Journal↗
USGS1999

Structural and petrologic evolution of the Lihue basin and eastern Kauai, Hawaii

The topography of the eastern part of the Hawaiian island of Kauai is dominated by the Lihue basin, a large (∼110 km 2 ) semicircular depression bounded by steep cliffs and partly filled by late rejuvenated-stage (or posterosional stage) volcanic material. As with other large, semicircular basins on ocean-island volcanoes, the subsurface geology and origin (e.g., structural collapse vs. fluvial erosion) of the Lihue basin are poorly understood. New analyses of samples collected from eastern Kauai and drill holes within the basin document several important features of the late-stage geologic evolution of Kauai. First, thick (>300 m) sequences of rejuvenated-stage Koloa Volcanics in the Lihue basin show systematic, basin-wide geochemical trends of increasingly incompatible elements with time, indicating a gradual decrease in the extent of partial melting of mantle sources with time. Second, beneath the rejuvenated-stage volcanics in the basin, a thin layer of postshield alkalic stage lavas (e.g., hawaiites and mugearites) overlies older shield-stage tholeiitic lavas of the Napali Member, indicating that the Lihue basin formed by structural collapse, not fluvial erosion. Third, a large (∼2–5 km 3 ) matrix-supported breccia, interpreted as deposits of one or more debris flows, is within the rejuvenated-stage volcanics throughout the basin, and correlates with surficial exposures of the Palikea Breccia west of the basin. Isotopic compositions of the bulk breccia are similar to those of tholeiites from the east side of Kauai, and distinct from those of west Kauai tholeiites. Clasts within the breccia are dominantly hawaiite and alkali gabbro. The source region of the breccia in the steep cliffs and highlands of the central massif to the west of the basin must contain magmatic products of an extensive postshield alkalic stage, including hawaiite flows and one or more large intrusive bodies or ponded sequences of alkali gabbro.

Hawaii↗
USGS1998

Estimation of the depth to the fresh-water/salt-water interface from vertical head gradients in wells in coastal and island aquifers

An accurate estimate of the depth to the theoretical interface between fresh, water and salt water is critical to estimates of well yields in coastal and island aquifers. The Ghyben–Herzberg relation, which is commonly used to estimate interface depth, can greatly underestimate or overestimate the fresh-water thickness, because it assumes no vertical head gradients and no vertical flow. Estimation of the interface depth needs to consider the vertical head gradients and aquifer anisotropy that may be present. This paper presents a method to calculate vertical head gradients using water-level measurements made during drilling of a partially penetrating well; the gradient is then used to estimate interface depth. Application of the method to a numerically simulated fresh-water/salt-water system shows that the method is most accurate when the gradient is measured in a deeply penetrating well. Even using a shallow well, the method more accurately estimates the interface position than does the Ghyben–Herzberg relation where substantial vertical head gradients exist. Application of the method to field data shows that drilling, collection methods of water-level data, and aquifer inhomogeneities can cause difficulties, but the effects of these difficulties can be minimized.

Hydrogeology Journal↗
USGS1996

Summary of ground-water and rainfall data for Tutuila and Aunuu Islands, Americn Samoa, for July, 1984 through September, 1995

Ground-water and rainfall data for the period from July 1984 through September 1995 from the islands of Tutuila and Aunuu have been summarized in time-series graphs that can be used to analyze for historical trends. The data include pumpage and chloride concentrations from 50 production wells on Tutuila and 3 production wells on Aunuu, water-level measurements from 12 wells on Tutuila, and rainfall from 2 gages on Tutuila. Rainfall averaged 13.2 inches per month at the rain gage at Afono near Pioa Mountain and 17.6 inches per month at the rain gage at Aasufou over the period from 1984 to 1995. Late 1987 to early 1992 was a dry period with below- average rainfall, whereas rainfall in 1994 through September 1995 was higher than average. The Tafunafou-Malaeimi-Mesepa well field and the Leone-Malaeloa well field each pumped about 2.4 to 4 million gallons per day. Chloride concentrations of water pumped from the well fields were usually less than 500 milligrams per liter but chloride concentrations have exceeded 500 milligrams per liter during periods when rainfall was below average. Iliili wells pumped about 1.3 to 1.4 million gallons per day from four production wells, three of which had chloride concentrations under 200 milligrams per liter, and the fourth having chloride concentrations usually under 500 milligrams per liter. Water in wells at Aua, Fagaitua, Alofau, Alao, Tula, and Sailele had chloride concentrations frequently in excess of 500 milligrams per liter. Water levels at Aua during pumping dropped as low as 60 ft below sea level. Chloride concentrations at Fagaalu, and Aoa have remained below 200 milligrams per liter and chloride concentrations at Fagasa have usually remained below 500 milligrams per liter. These well fields have been pumped for less than 5 years at pumpage rates of less than 0.1 million gallons per day at each well field. The Fagatogo and Pago Pago well fields have each produced about 0.75 to 1.0 million gallons per day while maintaining chloride concentrations below 100 milligrams per liter. Water levels in monitor wells in these well fields have dropped below sea level on occasion. Chloride concentrations on Aunuu frequently exceeded 500 milligrams per liter and reached nearly 2,000 milligrams per liter since the wells began pumping in 1992 at a rate of 0.01 to 0.03 million gallons per day each.

Open-File Report↗