We present new thermometers and barometers based on clinopyroxene-liquid equilibria specific to 37 alkaline differentiated magmas. The new models were calibrated through regression analyses of 38 experimental datasets obtained by merging phase equilibria experiments from literature with new 39 experiments performed by using trachytic and phonolitic starting compositions. The regression 40 strategy was twofold: i) we have tested previous thermometric and barometric equations and 41 recalibrated these models using the new datasets; ii) we have calibrated a new thermometer and a 42 new barometer including only regression parameters that closely describe the compositional 43 variability of the datasets. The new models yield more precise estimates than previous 44 thermometers and barometers when used to predict temperatures and pressures of alkaline 45 differentiated magmas. We have tested the reliability of the new equations by using clinopyroxene-46 liquid pairs from trachytes and phonolites erupted during major explosive eruptions at the Phlegrean 47 Fields and Mt. Vesuvius (central Italy). The test yielded crystallization conditions comparable to 48 those determined by means of melt and fluid inclusion analyses and phase equilibria studies; this 49 validates the use of the proposed models for precise estimates of crystallization temperatures and 50 pressures in differentiated alkaline magmas. Because these magmas feed some of the most 51 voluminous, explosive, and threatening volcanic eruptions in the world, a better understanding of 52 the environmental conditions of their reservoirs is mandatory and this is now possible with the new 53 models provided here. 54 55 56 table 2 Click here to download table: Table 2.doc

There is considerable evidence for ongoing, late-stage interaction between the magmatic system at Merapi volcano, Indonesia, and local crustal carbonate (limestone). Calc-silicate xenoliths within Merapi basaltic-andesite eruptives display textures indicative of intense interaction between magma and crustal carbonate, and Merapi feldspar phenocrysts frequently contain individual crustally contaminated cores and zones. In order to resolve the interaction processes between magma and limestone in detail we have performed a series of time-variable de-carbonation experiments in silicate melt, at magmatic pressure and temperature, using a Merapi basaltic-andesite and local Javanese limestone as starting materials. We have used in-situ analytical methods to determine the elemental and strontium isotope composition of the experimental products and to trace the textural, chemical, and isotopic evolution of carbonate assimilation. The major processes of magmacarbonate interaction identified are: i) rapid decomposition and degassing of carbonate, ii) generation of a Ca-enriched, highly radiogenic strontium contaminant melt, distinct from the starting material composition, iii) intense CO 2 vesiculation, particularly within the contaminated zones, iv) physical mingling between the contaminated and unaffected melt domains, and v) chemical mixing between melts. The experiments reproduce many of the features of magmacarbonate interaction observed in the natural Merapi xenoliths and feldspar phenocrysts. The Carich, high 87 Sr/ 86 Sr contaminant melt produced in the experiments is considered as a pre-cursor to the Ca-rich (often "hyper-calcic") phases found in the xenoliths and the contaminated zones in Merapi feldspars. The xenoliths also exhibit micro-vesicular textures which can be linked to the CO 2 liberation process seen in the experiments. This study, therefore, provides well-constrained petrological insights into the problem of crustal interaction at Merapi and points toward the substantial impact of such interaction on the volatile budget of the volcano.

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The recent Eyjafjallajökull (Iceland) eruption strikingly underlined the vulnerability of a globalized society to the atmospheric dispersal of volcanic clouds from even moderate-size eruptions. Ash aggregation controls volcanic clouds dispersal by prematurely removing fi ne particles from the cloud and depositing them more proximally. Physical parameters of ash aggregates have been modeled and derived from ash fallout deposits of past eruptions, yet aggregate sedimentation has eluded direct measurement, limiting our ability to predict the dispersal of volcanic clouds. Here we use fi eld-based, highspeed video analysis together with laboratory experiments to provide the fi rst in situ investigation and parameterization of the physical features and settling dynamics of ash aggregates from a volcanic cloud. In May 2010, high-speed video footage was obtained of both ash particles and aggregates settling from the Eyjafjallajökull volcano eruption cloud at a distance of 7 km from the vent; fallout samples were collected simultaneously. Experimental laboratory determinations of the density, morphology, and settling velocity of individual ash particles enable their distinction from aggregates. The combination of fi eld and experimental analyses allows a full characterization of the size, settling velocity, drag coeffi cient, and density distributions of ash aggregates as well as the size distribution of their component particles. We conclude that ash aggregation resulted in a tenfold increase in mass sedimentation rate from the cloud, aggravating the ash hazard locally and modifying cloud dispersal regionally. This study provides a valuable tool for monitoring explosive eruptions, capable of providing robust input parameters for models of cloud dispersal and consequent hazard forecast.