Different models have been proposed for the "drumbeat" earthquakes that accompanied recent eruptive behavior at Mount St. Helens. Debate continues as to whether seismicity is related to brittle failure during the extrusion of solid dacite spines or is the result of hydrothermal fluids interacting with a crack buried in the volcanic edifice. My model predictions of steady-state conduit flow conf...

Oxygen isotope data are reported for clinopyroxene phenocrysts from volcanic rock samples from Filicudi island, Italy, with the aim of investigating mechanisms of magma evolution and mantle source characteristics in a continental arc volcano. Filicudi rocks range from calc-alkaline basalt to high-K andesite and dacite. Mafic rocks have MgO 6-7 wt%, Mg# 60, Ni < 50 ppm and Cr < 200 ppm, suggesti...

We reanalyze the pressure dependence of viscosity of liquids of constant composition under isothermal conditions. Based exclusively on very general considerations concerning the relationship between viscosity and "free volume," we show that, at moderate values of pressure, viscosity increases, as a rule, with increasing pressure, provided the liquid is in stable or metastable (undercooled) equi...

Water is an important volatile component in andesitic eruptions and deep-seated andesitic magma chambers. We report an investigation of H2O speciation and diffusion by dehydrating haploandesitic melts containing 62.5 wt.% water at 743–873 K and 100 MPa in cold-seal pressure vessels. FTIR microspectroscopy was utilized to measure species [molecular H2O (H2Om) and hydroxyl group (OH)] and total H...

Abstract One of the longest arcs in world originated from complexity subduction zones is Sunda Arc that covers 80% Indonesia's active volcanoes, Andaman, Sumatra, Java, and Lesser Islands. Previous research magmatism has conceded continental crust west becomes progressively oceanic towards east. However, recent suggested basement more widespread than previously thought. Therefore, this study ai...

Areas ofvegetation mortality have been recognized in the upland forests of the Kaimai Ranges, North Island, New Zealand. The mortality is not confined to any particular vegetation type, but occurs above a critical altitude that differs at different points along the ranges. The mortality is episodic and has occurred at intervals over a period of several hundred years, with severe droughts implic...

We report the first systematic study of H2O speciation in dacitic melt with total dissolved H2O ranging from 1.4 to 2.6 wt%. Samples were heated in a one-atmosphere tube furnace at 480–590 °C for certain durations and then quenched in water or air. Species concentrations were measured with Fourier transform infrared (FTIR) spectroscopy. At a given temperature, the equilibrium constant for the r...