Crystallization history of Kilauea Iki lava lake as seen in drill core recovered in 1967–1979

Kilauea Iki lava lake formed during the 1959 summit eruption, one of the most picritic eruptions of Kilauea Volcano in the twentieth century. Since 1959 the 110 to 122 m thick lake has cooled slowly, developing steadily thickening upper and lower crusts, with a lens of more molten lava in between. Recent coring dates, with maximum depths reached in the center of the lake, are: 1967 (26.5 m). 1975 (44.2 m), 1976 (46.0 m) and 1979 (52.7 m). These depths define the base of the upper crust at the time of drilling. The bulk of the core consists of a gray, olivine-phyric basalt matrix, which locally contains coarser-grained diabasic segregation veins. The most important megascopic variation in the matrix rock is its variation in olivine content. The upper 15 m of crust is very olivine-rich. Abundance and average size of olivine decrease irregularly downward to 23 m; between 23 and 40 m the rock contains 5–10% of small olivine phenocrysts. Below 40 m. olivine content and average grainsize rise sharply. Olivine contents remain high (20–45%, by volume) throughout the lower crust, except for a narrow (< 6 m) olivine depleted zone near the basalt contact. Petrographically the olivine phenocrysts in Kilauea Iki can be divided into two types. Type 1 phenocrysts are large (1–12 mm long), with irregular blocky outlines, and often contain kink bands. Type 2 crystals are relatively small (0.5–2 mm in length), euhedral and undeformed. The variations in olivine content of the matrix rock are almost entirely variations in the amount of type 1 olivines. Sharp mineral layering of any sort is rare in Kilauea Iki. However, the depth range 41–52 m is marked by the frequent occurrence of steeply dipping (70°–90°) bands or bodies of slightly vuggy olivine-rich rock locally capped with a small cupola of segregation-vein material. In thin section there is clear evidence for relative movement of melt and crystals within these structures. The segregation veins occur only in the upper crust. The most widely distributed (occurring from 4.5–59.4 m) are thin veins (most < 5 cm thick), which cut the core at moderate angles and appear to have been derived from the immediately adjacent wall-rock by filter pressing. There is also a series of thicker (0.1–1.5 m) segregation veins, which recur every 2–3 m, between 20 and 52 m. These have subhorizontal contacts and appear, from similarities in thickness and spacing, to correlate between drill holes as much as 100 m apart. These large veins are not derived from the adjacent wallrock: their mechanism of formation is still problematical. The total thickness of segregation veins in Kilauea Iki is 3–6 m in the central part of the lake, corresponding to 6–11% of the upper crust. Whole-rock compositions for Kilauea Iki fall into two groups: the matrix rock ranges from 20-7.5% MgO, while the segregation veins all contain between 6.0 and 4.5% MgO. There are no whole-rock compositions of intermediate MgO content. Samples from < 12 m show eruption-controlled chemistry. Below that depth, matrix rock compositions have higher Al₂O₃, TiO₂ and alkalies, and lower CaO and FeO, at a given MgO content than do the eruption pumices. The probable causes of this are assimilation of low-melting components from foundered crust, plus removal of olivine, plus removal of minor augite, for rocks with MgO contents of < 8.0%. Given the observed rate of growth of the upper crust, one can infer that significant removal of the type 1 olivine phenocrysts from the upper part of the lake began in 1963 and ceased sometime prior to 1972. The process. probably gravitative settling, appears to have been inhibited earlier by gas streaming from the lower part of the lens of melt. The olivine cumulate zone, which extends into the upper crust, contains relatively few (25–40%) olivine crystals, few of which actually touch each other. The diffuseness of the cumulate zone raises the possibility that the crystals were coated with a relatively visous boundary layer of melt which moved with them. Calculations of the Stokes’ law settling rates of the largest olivine crystals found at the base of the crust in 1975–76 suggest that the «melt» had a viscosity of > 10⁶ poises, and probably had the properties of a Bingham body, rather than a Newtonian fluid, by that date, which was several years after olivine removal ceased.     

USEFULNESS OF WELL REGISTRATION DATA

Abstract. This investigation was to determine whether data on irrigation-well registration forms as reported by well drillers can be used in hydrologic studies. Transmissivity maps were prepared for Hamilton County, Nebraska using only specific capacity values computed from yield and drawdown data, as reported on irrigation well-registration forms. On one map each control point was the mean of the transmissivity values calculated for all wells in a section. On a second map each control point was the mean of the means for four contiguous sections sharing a common corner. The second map was similar to that of a previously prepared map based on control point values computed from specific capacities of selected wells, test hole logs, and geologic interpretations. These results suggest that reported registration data for a given area have a normal population distribution. In situations where individual data are unverified the data base can be treated as samples of a population where the mean of the means of several samples for adjacent areas is representative of actual field conditions.     

An experimental assessment of the added mass of some plates vibrating in water

A reservoir of water is contained by a concrete valley block, a ferrocement wall and a steel plate. Both wall and plate contain an array of pressure transducer sockets (Figures 1 and 2). Using the M.A.M.A.¹ equipment pure modes of vibration are excited. Frequency and mode shape are measured with the reservoir empty. When the reservoir is full hydrodynamic pressure is also measured. These hydrodynamic pressures are compared with Chopra's² two-dimensional, series solution, which includes compressibility of water, and with two- and three-dimensional finite element solutions of Laplace's equation, which do not include compressibility. Chopra's solution is unsatisfactory for modes which contain a vertical node line. The best agreement between experimental and theoretical hydrodynamic pressure is obtained when the latter is obtained from three-dimensional solutions of Laplace's equations, indicating that compressibility does not play a significant rǒle. This conclusion is supported by agreement between experimental frequencies (reservoir full) and those calculated using added mass obtained from the Laplace solution. Similar conclusions were reached from tests on a floating steel plate, suspended in the surface of the reservoir by a soft spring. Here, dynamic pressure measurements were not made, reliance being placed on agreement between calculated and measured frequencies and mode shapes.     

Effectiveness of a market-based instrument for the allocation of water in a tropical river environment

The seasonal nature of Australia’s tropical rivers means that connected groundwater aquifers are an important source of both consumptive and non-consumptive water, particularly during the dry season. The management of these common pool groundwater resources is one of the predominant water issues facing northern Australia. A national program of water reform stipulates the expansion of water trading as a key instrument for water allocation. The effectiveness of new institutional arrangements such as water markets will be determined mostly by how well they coordinate with local environmental requirements, local institutions and local norms. This paper describes a novel application of combined field work, institutional analysis, experimental economics and agent-based modeling to the analysis of a potential water market in the Katherine region of the Northern Territory, Australia. The effectiveness of different versions of the policy instrument is assessed in light of local conditions. Instruments that enable personal relationships and local institutions and norms to play a role in water management are found to be more effective in terms of both farming income and environmental impact.     

Data reporting norms for 40Ar/39Ar geochronology

Data reported in ⁴⁰Ar/³⁹Ar geochronology studies are commonly insufficient to allow computation of ages. This deficiency renders it difficult to compare ages based on different standards or constants, and often hinders critical evaluation of the results. Herein are presented an enumeration of the data that should be reported in all ⁴⁰Ar/³⁹Ar studies, including a discussion in support of these requirements. The minimum required data are identified and distinguished from parameters that are useful but may be derived from them by calculation. Finally, recommendations are made for metadata needed to document age calculations (e.g., from age spectrum or isochron analyses).     

Model study of the effect of the main ionospheric trough on oblique HF radiowave propagation

The purpose of this paper is to study the effect of the main ionospheric trough location on the form of oblique sounding ionograms on the Murmansk-St. Petersburg subauroral radio path. Using a mathematical model of the high-latitude ionosphere, we have calculated four different distributions of electron density along the radio path. One of the distributions has been obtained when the trough is absent, and the remaining three distributions contain troughs of approximately identical depth and width but located at different distances from the ends of the radio path. Using the program of two-dimensional ray tracing, we numerically synthesized oblique-incidence ionograms for each of the four obtained distributions of electron density. The calculations have shown that the location of the main ionospheric trough affects considerably the shape of oblique-incidence ionograms.     

A study in the dynamics of the geoelectrical medium from electrotelluric field data

The manner in which the dynamics of geoelectric earth inhomogeneities can be studied using receiving lines oriented in different directions at a single site is considered. It is shown that the presence of a local geoelectric inhomogeneity allows monitoring the state of electric conductivity in the earth by observation of the telluric tensor. We quote results from long-continued monitoring of the electrotelluric tensor in Kamchatka. The tensor’s behavior showed an appreciable anomaly, which may have been related to great (magnitude 8.2 and 8.3) earthquakes in the Kuril-Kamchatka region.     

Accumulation of Heavy Metals by Macrophytes at Different Levels of Pollution of Aquatic Medium

Data on heavy metals accumulation in higher aquatic plants in the Rybinsk Reservoir are presented. Some plants are shown to intensely accumulate metals depending on the degree of the reservoir pollution.     

B-polarization induction in two thin half-sheets coupled to the mantle by a conducting crust—II. Solution by the mode-matching method, the fields above the conductors, and example results

The mode-matching method is used to obtain an exact analytical solution to the problem of B -polarization induction in two adjacent thin half-sheets, lying on a conducting layer that is terminated by a perfect conductor at finite depth. These components of the model represent, respectively, the Earth's conducting surface layers, crust, and mantle. In dimensionless variables, the model has three independent parameters, these being the two thin-sheet conductances and the layer thickness. The mode-matching solution obtained in this paper is shown to be identical lo that derived via the Wiener-Hopf method in a companion paper (Dawson 1996), and so provides additional verification of that solution. As was shown in the companion paper, the solution for the present model contains, as special limiting cases, those for three models considered earlier by various authors. The second part of the present paper addresses the solutions for the electric fields in the non-conducting half-space above the conductors, which represents the atmosphere. In the final part, sample numerical calculations are presented to illustrate the solution.