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  • 1
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    Control of magma flow in dykes on cyclic lava dome extrusion (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time-scales ranging from hours to decades. Examples include Bezymianny volcano (Russia), Merapi (Java), Santiaguito (Guatemala), Mt St Helens (USA), Mt Unzen (Japan), and Soufrie`re Hills volcano (Montserrat). Previous models have assumed simple cylindrical conduits for magma transport, but extrusions are mainly fed by dykes, with cylindrical geometries developing only at shallow levels. The widths of dykes embedded in an elastic medium are influenced by local magma pressure, affecting flow rates and system dynamics strongly. We develop a model for magma flow in dykes, which predicts intense pulsations of magma extrusion for the case of a constant source pressure. The period time scale is determined by the elastic deformation of the dyke walls and the length-to-width ratio of the dyke. The dyke acts like a volumetric capacitor, storing magma as pressure increases and then releasing magma in a pulse of extrusion. For the Soufrie`re Hills volcano, cyclic extrusions with time-scales of a few weeks are predicted for dykes 300–500 m long and 3–6 m wide, matching observations. The model explains the sharp onset of tilt pulsations and seismic swarms.
    Description: Published
    Description: L02303
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Control ; magma flow ; dykes ; cyclic lava ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Volcanic Eruptions: Cyclicity During Lava Dome Growth (2007)
    Details
    Publication Date: 2017-04-04
    Description: We consider the process of slow extrusion of very viscous magma that forms lava domes. Domebuilding eruptions are commonly associated with hazardous phenomena, including pyroclastic flows generated by dome collapses, explosive eruptions and volcanic blasts. These eruptions commonly display fairly regular alternations between periods of high and low or no activity with time scales from hours to years. Usually hazardous phenomena are associated with periods of high magma discharge rate, thus, understanding the causes of pulsatory activity during extrusive eruptions is an important step towards forecasting volcanic behaviour, especially the transition to explosive activity when magma discharge rate increases by a few orders of magnitude. In recent years the risks have increased because the population density in the vicinity of many active volcanoes has increased.
    Description: Submitted
    Description: 3.6. Fisica del vulcanismo
    Description: N/A or not JCR
    Description: open
    Keywords: Volcanic Eruptions ; Cyclicity ; During Lava ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: manuscript
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  • 3
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    Controls of conduit geometry and wallrock elasticity on lava dome eruptions (2007)
    elsevier
    Details
    Publication Date: 2017-04-04
    Description: Many lava dome building eruptions show periodic to complex non-periodic pulsatory activity. Typical time-scales associated with this activity range from hours to decades. Previous studies modelled the ascent of magma using a set of transient 1-D transport equations, accounting for degassing induced crystallization kinetics, gas exsolution and viscosity increase due to crystal growth. These models assumed flow in a cylindrical conduit with a fixed cross-section area. Since several observations suggest that extrusions are mainly fed by dykes, with cylindrical geometries developing only at shallow levels, here we generalised the model to the flow geometry represented by an elliptical dyke with major and minor semi-axes changing with depth. Quasi-static elastic deformation of the dyke is accounted by an analytical solution that couples cross-section area with the magmatic overpressure. The effects of the main dyke geometrical parameters and boundary conditions on the eruption dynamics were investigated. The presence of a deformable dyke can lead to a more complex periodic behaviour with a wider range of time-scales and cyclicity patterns with respect to a uniform cylindrical conduit. There is a regime where the period of pulsations is controlled by the elasticity of the dyke and a regime where the period is controlled by the volume of the magma chamber. Intermediate regimes are possible. Periodic variations in discharge rate are also possible for both fixed pressure in dyke source region and fixed influx rate into the dyke. Our study emphasizes the strong nonlinearities and complex behaviours of lava dome eruptions. From a forecasting and hazard perspective, intrinsic uncertainties in governing parameters may make volcanic systems in some circumstances unpredictable. On the other hand, lava dome systems may also develop episodic and systematic behaviours so that behaviour becomes predictable for a while.
    Description: Published
    Description: 137–151
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: lava dome ; extrusive eruption ; dyke ; wallrock elasticity ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Thermal effects during magma ascent in conduits (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: Because of strong coupling between viscosity and temperature, the dynamics of magma flows in conduits are drastically controlled by thermal effects due to heat generation by viscous dissipation and loss to the walls by conduction. Here we present analytical solutions and a practical procedure based on an order of magnitude analysis that permits the characterization of the regime and estimation of the main features of the flow. The ranges of validity of analytical and asymptotic solutions were bounded by using results from fully two-dimensional (2-D) numerical solutions of mass, momentum, and energy equations for magma flow inside a cylindrical conduit and the heat conduction in the surrounding host rocks. The results permitted the identification of three regimes: a conductive-heat-loss-dominated regime, an intermediate regime, and a viscous-heating-dominated regime. Some useful analytical parameterizations are proposed for estimating friction in simplified 1-D models. Temperature layering due to heat loss by conduction can lead to local crystal growth and magma solidification whereas heat generated by viscous dissipation can be responsible for crystal resorption and remelting of wall rocks
    Description: Published
    Description: B12205
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: partially_open
    Keywords: magma conduit ; thermal budget ; viscous dissipation ; heat loss ; temperature-dependent viscosity ; nonlinear effects ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Volcanic Eruptions:Cyclicity during Lava Dome Growth (2008)
    Springer
    Details
    Publication Date: 2017-04-04
    Description: We consider the process of slow extrusion of very viscous magma that forms lava domes. Dome-building eruptions are commonly associated with hazardous phenomena, in- cluding pyroclastic flows generated by dome collapses, explosive eruptions and volcanic blasts. These eruptions commonly display fairly regular alternations between pe- riods of high and low or no activity with time scales from hours to years. Usually hazardous phenomena are asso- ciated with periods of high magma discharge rate, thus, understanding the causes of pulsatory activity during ex- trusive eruptions is an important step towards forecasting volcanic behavior, especially the transition to explosive ac- tivity when magma discharge rate increases by a few orders of magnitude. In recent years the risks have increased be- cause the population density in the vicinity of many active volcanoes has increased.
    Description: Published
    Description: 3.6. Fisica del vulcanismo
    Description: open
    Keywords: Volcanic Eruptions ; Cyclicity ; During Lava ; 04. Solid Earth::04.01. Earth Interior::04.01.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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