GNGTS 2017 - 36° Convegno Nazionale

200 GNGTS 2017 S essione 1.3 Acknowledgments This work has been supported by the Italian Department of Civil Protection, the EPOS-IP project of the European Union Horizon 2020 research and innovation program under grant agreement 676564, the ESA GEP project, and the I-AMICA project (Infrastructure of High Technology for Environmental and Climate Monitoring-PONa3_00363). Sentinel-1 data are copyright of Copernicus (2017). COSMO-SkyMed data are copyright of ASI (2017), and they have been acquired through a dedicated acquisition plan. The contents of this work represent the Authors’ ideas and do not necessarily correspond to the official opinion and policies of the National Department of Civil Protection (Italy). References Carlino, S. (2012). The process of resurgence for Ischia Island (Southern Italy) since 55 ka: the laccolith model and implications for eruption forecasting. Bulletin of Volcanology, 74(5), 947-961. Changes in lava effusion rate due to pressure changes in the volcanic conduit M. Dragoni 1 , A. Tallarico 2 1 Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Università di Bologna, Italy, 2 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi Aldo Moro, Bari, Italy Effusive eruptions show a characteristic time history of the effusion rate, increasing from zero to a maximum and then slowly decreasing and vanishing at the end of the eruption (e.g. Vicari et al., 2011; Del Negro et al., 2012). A pioneering paper by Wadge (1981) reproduced the decrease in effusion rate as a consequence of the decrease of pressure gradient in the volcanic conduit due to progressive emptying of the magma chamber. More recently, the global time history of effusion rate has been reproduced by Piombo et al. (2016) by considering the mechanical erosion of the conduit wall produced by magma flow. During effusive eruptions, such as those on Mt. Etna, changes in the effusion rate are also observed having much shorter durations than the total duration of the eruption (e.g. Lautze et al., 2004). Similar observations have been made on other volcanoes characterized by more explosive activity (e.g. Voight et al., 1999). As a cause of such changes, one may envisage two main possibilities: (1) fluctuations in the supply rate from the magma chamber and/or (2) conduit processes that interfere with an approximately constant supply rate. With regard to the latter processes, several mechanisms have been proposed. Whitehead and Helfrich (1991) suggested that flow oscillations may result from temperature changes in a fluid with a temperature-dependent viscosity. Woods and Koyaguchi (1994) showed that for small chamber overpressures a nonuniqueness of eruption rate may result, leading to transitions between effusion and explosive eruptions. Ida (1996) suggested rapid changes in the width of the conduit outlet by viscous flow of wall rocks. Wylie et al. (1999) showed that an oscillatory behaviour of magma flow may be due to the dependence of viscosity on the volatile content of the magma. Observations at Stromboli volcano indicate that mass flow may proceed in a pulsatory manner. Positively correlated variations in degassing and explosive activity have been recorded, with 5-40 min phases characterized by either vigorous or weak degassing. This suggests that they are due to pressure changes in the conduit associated with changes in volatile content. Effusion rate and degassing data collected at Mt. Etna in 2001 show variations occurring on time scales of hours to months. In the present paper, we calculate the change in magma flow rate following from pressure changes in the volcanic conduit. To this aim, we consider a cylindrical conduit embedded in an elastic medium. A constant pressure gradient is assumed to drive the magma flow through the conduit. We assume that pressure oscillates around an equilibrium value and calculate the