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Composite volcanoes can progressively weaken through hydrothermal alteration, which may lead to volcano collapse, forming far-reaching debris avalanches. This work reviews and synthesises the type and extent of hydrothermal alteration on Mt. Ruapehu, New Zealand, from rock mechanical, mineralogical, hyperspectral imaging and aero-magnetic studies for input into the first debris avalanche models of Mt. Ruapehu. Mt. Ruapehu shows surface weathering processes, forming goethite, hematite and phyllosilicate assemblages, and hydrothermally altered rock, with phyllosilicate, Fe- oxides and sulphates, pyrite, jarosite, alunite, anhydrite and sulphur. The surface alteration mapped by hyperspectral remote sensing is linked to the deep-seated (≤500 m) alteration by aero-magnetic inversion modelling. Textural analysis and mapping show that alteration weathering and porosity distribution are a result of the both the primary lithology, age, and location relative to active or fossil hydrothermal systems. The synthesis of the aero-magnetic data, previous magnetotelluric models, hyperspectral and hydrothermal mapping, and rock mechanics studies enabled the construction of a schematic model to provide inputs for modelling potential flank failure zones. These models suggest that the southwest and west flanks of Mt. Ruapehu have the highest probability of collapsing and generating debris avalanches. [ABSTRACT FROM AUTHOR]

Hydrothermal alteration zoning and processes provide insights into the evolution of heat source(s) and fluid compositions associated with geothermal systems. Traditional petrological techniques, combined with hydrothermal alteration studies, stable isotope analyses and geochronology can resolve the nature of the fluids involved in hydrothermal processes and their changes through time. We report here new findings along with previous unpublished works on alteration patterns, fluid inclusion measurements and stable isotope data to provide insights into the thermal and chemical evolution of the Kawerau geothermal system, New Zealand. These data indicate the presence of two hydrothermal events that can be coupled with chronological data. The earlier period of hydrothermal activity was initiated at ~400 ka, with the heat driving the hydrothermal system inferred to be from the magmatic system that gave rise to rhyolite lavas and sills of the Caxton Formation. Isotopic data fingerprint fluids attributed to this event as meteoric, indicating that the magma primarily served as a heat source driving fluid circulation, and was not releasing magmatic fluids in sufficient quantity to affect the rock mineralogy and thus inferred fluid compositions. The modern Kawerau system was initiated at ~16 ka with hydrothermal eruptions linked to shallow intrusion of magma at the onset of activity that gave rise to the Putauaki andesite cone. Likely associated with this later event was a pulse of magmatic CO 2 , resulting in large-scale deposition of hydrothermal calcite enriched in 18 O. Meteoric water-dominated fluids subsequently overwhelmed the magmatic fluids associated with this 18 O-rich signature, and both the fluid inclusion microthermometry and stable isotope data reflect a change to the present-day fluid chemistry of low salinity, meteoric-dominated waters. [ABSTRACT FROM AUTHOR]

The single-step hydrothermal technique was used to synthesize nickel (II) oxide-zinc nitrate hexahydrate (NZ), hexagonal-shaped nanorods for high-performance supercapacitors applications (SC). The structural morphology and physical properties of the NZ nanocomposite were investigated via XRD, FESEM, HRTEM, XPS, and Raman spectroscopy. Among the prepared nanocomposite, NZ-10 shows the most significant properties, which were used for the fabrication of all-solid-state symmetric supercapacitors (SSC). Electrochemical analysis of the Galvano charging-discharging (GCD) curves achieved a high specific capacitance (Csp) of 665.4 Fg-1 at a current density (CD) of 1 Ag-1. The cyclic Voltammetry (CV) curve for the electrode shows a high Csp of 514.4 Fg-1 at a scan rate of 10 mV/s. Even after 5000 repeated cycles, it maintains strong cyclic stability, with capacitance retention of 73.43% and a coulombic efficiency of 96.12%. In addition, the NZ-10 composite has a high energy density (ED) of 26.73 Whkg−1 and a power density (PD) of 641.5 Wkg-1. In addition, the SSC device is connected in series to switch on a commercial blue LED that lasts 2–3 min and has a voltage drop of 2.71 V. As a result, these electrochemical performances are the highest in these materials, and they may be a good aspirant to fabricate advanced active materials for high-performance SC applications. [Display omitted] • The inimitable NZ hexagonal nanorod assembly was synthesised via a single-step hydrothermal method. • The NZ-10 reveals that in an aqueous electrolyte, the high specific capacitance is 665.4 Fg-1 at a current density of 1 Ag-1. • The symmetric SSC device has a power density of 641.5 Whkg−1 and an energy density of 26.73 Whkg−1. • It has excellent cyclical stability with capacity retention of 73.43% and coulombic efficiency of 96.12%, even after 5000 cycles. • The practical implementation of this electrode has been proven by lighting the blue LED for more than 2–3 min with a voltage drop of 2.71 V. [ABSTRACT FROM AUTHOR]