The crater lake and hydrothermal system of Mount Pinatubo,Philippines: evolution in the decade after eruption

The June 1991 eruption of Mount Pinatubo, Philippines breached a significant, pre-eruptive magmatic-hydrothermal system consisting of a hot (>300 °C) core at two-phase conditions and surrounding, cooler (<260 °C) liquid outflows to the N and S. The eruption created a large, closed crater that accumulated hydrothermal upwellings, near-surface aquifer and meteoric inflows. A shallow lake formed by early September 1991, and showed a long-term increase in level of ~1 m/month until an artificial drainage was created in September 2001. Comparison of the temporal trends in lake chemistry to pre- and post-eruptive springs distinguishes processes important in lake evolution. The lake was initially near-neutral pH and dominated by meteoric influx and Cl–SO₄ and Cl–HCO₃ hydrothermal waters, with peaks in SO₄ and Ca concentrations resulting from leaching of anhydrite and aerosol-laden tephra. Magmatic discharge, acidity (pH~2) and rock dissolution peaked in late 1992, during and immediately after eruption of a lava dome on the crater floor. Since cessation of dome growth, trends in lake pH (increase from 3 to 5.5), temperature (decline from 40 to 26 °C), and chemical and isotopic composition indicate that magmatic degassing and rock dissolution have declined significantly relative to the input of meteoric water and immature hydrothermal brine. Higher concentrations of Cl, Na, K, Li and B, and lower concentrations of Mg, Ca, Fe, SO₄ and F up to 1999 highlight the importance of a dilute hydrothermal contribution, as do stable-isotope and tritium compositions of the various fluids. However, samples taken since that time indicate further dilution and steeper trends of increasing pH and declining temperature. Present gas and brine compositions from crater fumaroles and hot springs indicate boiling of an immature Cl–SO₄ geothermal fluid of near-neutral pH at approximately 200 °C, rather than direct discharge from magma. It appears that remnants of the pre-eruptive hydrothermal system invaded the magma conduit shortly after the end of dome emplacement, blocking the direct degassing path. This, along with the large catchment area (~5 km²) and the high precipitation rate of the area, led to a rapid transition from a small and hot acid lake to a large lake with near-ambient temperature and pH. This behavior contrasts with that of peak-activity lakes that have more sustained volcanic gas influx (e.g., Kawah Ijen, Indonesia; Poas and Rincón de la Vieja, Costa Rica).Editorial responsibility: H. Shinohara     

Regolith-atmosphere exchange of water and carbon dioxide on Mars: Effects on atmospheric history and climate change

Exchange of CO₂ and H₂O between the Mars regolith and the atmosphere-cap system plays an important role in governing the evolution of the martian atmosphere and the martian climate. Most of the exchangeable CO₂ (perhaps one or two orders of magnitude more than the atmospheric inventory) is currently adsorbed on the deep regolith, and can be “cryopumped” to a large quasipermanent CO₂ cap (not now present) during lowest Mars obliquity (θ). During the obliquity driven regolith-cap CO₂ exchange cycle, the atmospheric pressure varies harmonically between ~0.1 mb (lowest Θ) and ? 20 mb (highest Θ). The regolith buffer plays only a small or negligible role in the seasonal CO₂ pressure variations caused by atmosphere-cap exchange because adsorption greatly inhibits diffusion of the seasonal “pressure wave” into the regolith. In contrast, thermally driven H₂O seasonal exchange between the atmosphere and regolith appears to be in large part responsible for observed seasonal variations in the small atmospheric H₂O inventory. Long term exchange of H₂O may be dominated by transfer between the polar caps and ice in the regolith. Available and potential tests of regolith-atmospheric-cap volatile exchange models using ground-based and spacecraft-based techniques are discussed.     

AXIOM: advanced X-ray imaging of the magnetosphere

Planetary plasma and magnetic field environments can be studied in two complementary ways—by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth’s magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques, which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth’s magnetosphere. In this article we describe how an appropriately designed and located X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock, with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth’s magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose ‘AXIOM: Advanced X-ray Imaging of the Magnetosphere’, a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth–Moon L1 point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterise the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission.     

Kilofarms in The Agricultural Heartland

Kilofarms are farms of 1,000 acres or more. The U.S. Department of Agriculture's Census of Agriculture has few tabulations of data by farm size, but geographical analysis suggests some of the characteristics of kilofarms. Their operators are part‐owner farmers. Their land and buildings are worth several millions of dollars, and their gross annual income is well over the $250,000 necessary to provide an acceptable level of living for a contemporary farm family. Kilofarmers concentrate on growing crops of corn and soybeans for cash sale, and they rely on computers and Internet access to help them make marketing decisions.     

The petrogenesis of group 2 ultrapotassic kimberlites from Finsch Mine, South Africa

Major, trace element and radiogenic isotope results are presented for a suite of hypabyssal kimberlites from a single pipe, at the Finsch Mine, South Africa. These are Group 2 kimberlites characterised by abundant phlogopite ± serpentine ± diopside; they are ultrabasic (SiO₂ < 42 wt.%%) and ultrapotassic (K₂O/Na₂O > 6.9) igneous rocks, they exhibit a wide range in major element chemistry with SiO₂ = 27.6−41.9 wt. % and MgO = 10.4−33.4 wt. %. (⁸⁷Sr/⁸⁶Sr)_i=0.7089 to 0.7106, ε_{Nd is} −6.2 to −9.7 and they have unradiogenic (²⁰⁷Pb/²⁰⁴Pb)_i contents which ensure that they plot below the Pb-ore growth curve. They have high incompatible and compatible element contents, a striking positive array between Y and Nb which indicates that garnet was not involved in the within suite differentiation processes, and a negative trend between K/Nb and Nb contents which suggests that phlogopite was involved. In addition, some elements exhibit an unexpected order of relative incompatibility for different trace elements which suggests that the intra-kimberlite variations are not primarily due to variations in the degree of partial melting. The effects of fractional crystallization are difficult to establish because for the most part they have been masked by the entrainment of 50–60% mantle peridotite. Thus, the Finsch kimberlites are interpreted as mixtures of a melt component and entrained garnet peridotite, with no evidence for significant contamination with crustal material. The melt component was characterised by high incompatible element contents, which require both very small degrees of partial melting, and source regions with higher incompatible element contents than depleted or primitive mantle. Since the melt component was the principal source of incompatible elements in the kimberlite magma, the enriched Nd, Sr and Pb isotope ratios of the kimberlite are characteristic of the melt source region. The melt fractions were therefore derived from ancient, trace elements enriched portions of the upper mantle, most probably situated within the sub-continental mantle lithosphere, and different from the low ⁸⁷Sr/⁸⁶Sr garnet peridotite xenoliths found at Finsch. Within the sub-continental mantle lithosphere old, incompatible element enriched source regions for the kimberlite melt fraction are inferred to have been overlain by depleted mantle material which became entrained in the kimberlite magma.     

Scheduling for Robonet‐1 homogenous telescope network

The Robonet‐1 homogenous telescope network consists of 3 fully robotic 2 m class telescopes. I describe how the observation requests submitted by external users and automated user agents are selected for observation by the individual telescope schedulers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)