We present multidisciplinary observations of the March-June 2011 VEI 2 eruptive episode of the basalticandesite Telica volcano, Nicaragua, which allow for a comprehensive study of the eruption mechanics of low-explosivity eruptions at persistently active volcanoes. The observations are from a dense network of seismic and GPS instrumentation augmented by visual observations of the eruptive episode, geochemical and petrologic analysis of eruptive products, plume SO2 measurements, and temperature measurements of fumaroles inside and outside the active vent. The 2011 eruptive episode was Telica's most explosive since 1999 and consisted of numerous vulcanian explosions, with maximum column heights of 1.5-2 km above the crater rim, depositing a low volume of dominantly hydrothermally altered ash. Based on observed variations in seismicity, temperature, and SO2 flux, the lack of deformation of the edifice, the non-juvenile origin of and predominance of accretionary lapilli in the ash, we propose that temporary sealing of the hydrothermal system between similar to 0.5 and 2 km depth, allowed pressure to build up prior to vulcanian explosions, making this a phreatic eruptive episode. (C) 2013 Elsevier B.V. All rights reserved.

We present a method for calculating quantitative melting reactions in systems with multiple solid solutions that accounts for changes in the mass proportions of phases between two points at different temperatures along a melting curve. This method can be applied to any data set that defines the phase proportions along a melting curve. The method yields the net change in mass proportion of all phases for the chosen melting interval, and gives an average reaction for the melting path. Instantaneous melting reactions can be approximated closely by choosing sufficiently small melting intervals. As an application of the method, reactions for melting of model upper mantle peridotite are calculated using data from the system CaO-MgO-Al2O3-SiO2-Na2O (CMASN) over the pressure interval 0.7-3.5 GPa. Throughout almost this entire pressure range, melting of model Iherzolite involves the crystallization of one or more solid phases, and is analogous to melting at a peritectic invariant point, In addition, we show that melting reactions for small melting intervals(< 5%) along the solidus of mantle peridotite are significantly different from those calculated for large melting intervals. For large melting intervals (> 10%), reaction stoichiometries calculated in CMASN are usually in good agreement with those available for melting of natural peridotite, The coefficients of melting reactions calculated from this method can be used in equations that describe the behavior of trace elements during melting. We compare results from near-fractional melting models using (1) melting reactions and rock modes from CMASN, and (2) constant reactions representative of those used in the literature. In modeling trace element abundances in melt, significant differences arise for some elements at low degrees of melting(< 10%). In modeling element abundances in the residue, differences increase with increase in degree of melting. Reactions calculated along the model Iherzolite solidus in CMASN are the only ones available at present for small degrees of melting so we recommend them for accurate trace element modeling of natural lherzolite.

Although volcano-tectonic (VT) earthquakes often occur in response to magma intrusion, it is rare for them to have magnitudes larger than similar to M4. On 24 May 2007, two shallow M4+ earthquakes occurred beneath the upper part of the east rift zone of Kilauea Volcano, Hawai'i. An integrated analysis of geodetic, seismic, and field data, together with Coulomb stress modeling, demonstrates that the earthquakes occurred due to strike-slip motion on pre-existing faults that bound Kilauea Caldera to the southeast and that the pressurization of Kilauea's summit magma system may have been sufficient to promote faulting. For the first time, we infer a plausible origin to generate rare moderate-magnitude VTs at Kilauea by reactivation of suitably oriented pre-existing caldera-bounding faults. Rare moderate-to large-magnitude VTs at Kilauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes.

The ''excess'' of siderophile elements in Earth's mantle is a long-standing problem in understanding the evolution of Earth. Determination of the partitioning behavior of tungsten and molybdenum between liquid metal and silicate melt at high pressure and temperature shows that partition coefficients (D-metal/silicate) vary by two orders of magnitude depending on whether metal segregated from a basaltic or peridotitic melt. This compositional dependence is likely a response to changes in the degree of polymerization of the silicate melt caused by compositional variations of the network-modifying cations Mg2+ and Fe2+. Silicate melt compositional effects on partition coefficients for siderophile elements are potentially more important than the effects of high pressure and temperature.

Synchrotron infrared measurements were conducted on a self-doped La(x)MnO(3-delta) (x similar to 0.8) film. From these measurements we determined the conductivity and the temperature dependence of the effective number of carriers. While the metal-insulator transition temperature (T(MI)) and the magnetic ordering temperature (T(C)) approximately coincide, the onset of the change in the free carrier density occurs at a significantly lower temperature (similar to 45 K below). This suggests that local distortions exist below T(MI) and T(C) which trap the e(g) conduction electrons. These regions with local distortions constitute an insulating phase which persists for temperatures significantly below T(MI) and T(C).

Telica Volcano, Nicaragua, is a persistently restless volcano with daily seismicity rates that can vary by orders of magnitude without apparent connection to eruptive activity. Low-frequency (LF) events are dominant and peaks in seismicity rate show little correlation with eruptive episodes, presenting a challenge for seismic monitoring and eruption forecasting. A short period seismic station (TELN) has been operated on Telica's summit since 1993, and in 2010 the installation of a six-station broadband seismic and eleven-station continuous GPS network (the TESAND network) was completed to document in detail the seismic characteristics of a persistently restless volcano. Between our study period of November 2009 and May 2013, over 400,000 events were detected at the TESAND summit station (TBTN), with daily event rates ranging from 5 to 1400. We present spectral analyses and classifications of -200,000 events recorded by the TESAND network between April 2010 and March 2013, and earthquake locations for a sub-set of events between July 2010 and February 2012. In 2011 Telica erupted in a series of phreatic vulcanian explosions. Six months before the 2011 eruption, we observe a sudden decrease in LF events concurrent with a swarm of high-frequency (HF) events, followed by a decline in overall event rates, which reached a minimum at the eruption onset. We observe repeated periods of high and low seismicity rates and suggest these changes in seismicity represent repeated transitions between open-system and closed-system degassing. We suggest that these short- and long-term transitions between open to closed-system degassing form part of a long-term pattern of stable vs. unstable phases at Telica. Stable phases are characterised by steady high-rate seismicity and represent stable open-system degassing, whereas unstable phases are characterised by highly variable seismicity rates and represent repeated transitions from open to closed-system degassing, where the system is unable to sustain steady open-system degassing. These observations have implications for seismic monitoring at persistently restless volcanoes as the recognition of unstable seismic phases may indicate the open-system degassing process cannot be sustained and explosions are likely. (C) 2014 The Authors. Published by Elsevier B.V.

We propose a model for the generation of average MORBs based on phase relations in the CaO-MgO-Al2O3-SiO2-CO2 system at pressures from 3 to 7 GPa and in the CaO-MgO-Al2O3-SiO2-Na2O-FeO (CMASNF) system at pressures from similar to0.9 to 1.5 GPa. The MELT seismic tomography (Forsyth et al., 2000) across the East Pacific Rise shows the largest amount of melt centered at similar to30-km depth and lesser amounts at greater depths. An average mantle adiabat with a model-system potential temperature (T-P) of 1310degreesC is used that is consistent with this result. In the mantle, additional minor components would lower solidus temperatures similar to50degreesC, which would lower T-P of the adiabat for average MORBs to similar to1260degreesC. The model involves generation of carbonatitic melts and melts that are transitional between carbonatite and kimberlite at very small melt fractions (<0.2%) in the low-velocity zone at pressures of similar to2.6 to 7 GPa in the CMAS-CO2 system, roughly the pressure range of the PREM low-velocity zone. These small-volume, low-viscosity melts are mixed with much larger volumes of basaltic melt generated at the plagioclase-spinel lherzolite transition in the pressure range of similar to0.9 to 1.5 GPa.

We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533022]

Seismic anisotropy, measured through shear wave splitting (SWS) analysis, can be indicative of the state of stress in Earth's crust. Changes in SWS at Kilauea Volcano, Hawai'i, associated with the onset of summit eruptive activity in 2008 hint at the potential of the technique for tracking volcanic activity. To use SWS observations as a monitoring tool, however, it is important to understand the cause of seismic anisotropy at the volcano throughout the eruptive cycle. To address this need, we analyzed SWS results from across Kilauea in combination with macroscopic surface structures (mapped fractures, faults, and fissures) and stress orientations inferred from fault plane solutions. Seismic anisotropy seems to be due to pervasive aligned structures in most regions of the volcano. The upper East and Southwest Rift Zones, however, show a bimodality in stress and SWS, suggesting a stress discontinuity with depth, perhaps related to magma conduits that trend obliquely to the dominant structure. Other areas in and around Kilauea Caldera display principal stresses of similar magnitudes, indicating that small stress perturbations can rotate the maximum horizontal compressive stress direction by up to 90 degrees. In these locations, static structures generally control SWS, but dynamic conditions due to magmatic activity can override the structural control. Monitoring of SWS may therefore provide important signs of impending volcanism.