Project

Discipline

Basaltic Volcanism; Explosive Volcanism; Eruption dynamics; Conduit flow dynamics; Analogue experiments; Villarrica; Stromboli; volcanic risk; geophysics; fluid dynamics; laboratory experiments

Lead
Lay summary
The project focuses on the study of the mechanisms controlling conduit-flow processes of basaltic magmas. Basaltic magmas have high temperatures, low viscosity, very variable volatile content, and are usually considered to generate low explosivity eruptions. However, many central volcanoes, such as Etna and Stromboli (Italy), Villarrica (Chile), Masaya (Nicaragua), and Shishaldin (USA), display a large variability in eruptive styles, and their eruptions may change in intensity from ~102 to more than 108 kg/s (peak magma discharge rate). Moreover, even single basaltic eruptions usually have long durations (days to weeks) and strong fluctuations in eruptive intensity, which can range from effusion of lava flows, to formation of a few m high lava fountains, or up to several km high eruptive plumes which disperse materials up to hundreds of km from the vent. At the moment these variations can hardly be predicted and significantly increase the risk to which populations living in the surroundings are exposed. Moreover, there is only limited comprehension of the dynamics of basaltic magma rise along the volcanic conduit and its effects on magma fragmentation mechanisms and on the variability of the explosive style. In fact, the study of eruptive events can characterize variability and style but does not give direct information on subsurface (magma rise in the volcanic conduit) phenomena.Because of the difficulty to obtain direct observations from the natural phenomena we will combine experimental analyses with geophysical monitoring of real eruptions at type volcanoes. We will compare scaled experimental results with eruptions from type volcanoes through geophysical observations (which define the eruptive style) and characterization of the erupted products (which reflect conduit and fragmentation dynamics). In particular, we will explore the transition between different two-phase flow regimes under different initial conditions (mainly different viscosity and gas flux), investigate the effects of conduit geometry on gas segregation by building and running experiments on a new rig with rectangular cross section at the University of Geneva, and relate results from geophysical surveys at Villarrica (Chile) and Stromboli (Italy) volcanoes with the results from the experiments, in order to better understand the significance of the structure of basaltic scoria in relation to gas-segregation dynamics, and parameterize the main processes controlling flow regime stability and structure of the magma column in the conduit. This project will involve an international research team, also comprising a postdoctoral researcher.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

The project “Two-phase flows of low-viscosity magmas” focuses on the study of the mechanisms controlling conduit-flow processes of mafic magmas. Mafic magmas display a large variety of eruptive manifestations, including highly explosive behavior, and even single eruptions may strongly change in intensity of several orders of magnitude. At the moment these variations can hardly be predicted and significantly increase the risk to which populations living in the surroundings are exposed. With the research project “Two-phase flows of low-viscosity magmas” currently funded by the SNSF (November 2009-October 2010) we have already started investigating the two-phase flow dynamics of the upper portion of the volcanic conduit to explore the conditions of ascent of basaltic magmas and their effect on the explosive style. We have addressed this topic through both experimental and field activities (i.e. geophysical monitoring). First, we have investigated the two-phase flow dynamics and regime transitions of viscous fluids in cylindrical conduits using a dedicated 6.5m-high bubble column. Our scaled experiments have shown that continuous gas flux through a liquid column results in a periodic flow marked by oscillations of the entire bubble column. Gas flux controls not only the flow regime stability, but also the frequency and amplitude of oscillations, and vesicularity of the mixture. Regime transitions can be correlated to specific gas fluxes and superficial velocities. Second, we have also recorded the seismic, infrared and acoustic signal of passive degassing at a single-vent system (i.e. Villarrica volcano, Chile), which is, in fact, characterized by very regular infrasonic and seismic oscillations similar to the pressure oscillations recorded in our cylindrical column. The current 2-year funded project was crucial to deal with basic questions of two-phase flow dynamics in low-viscosity magmas (e.g. regime transitions, similarities between experiments and natural systems), but it also produced new fundamental questions that need to be addressed in order to develop a deep understanding of the eruptive behavior of low-viscosity magmas. In particular, with the proposed project extension, we are planning i) to investigate further the dynamics of two-phase flows (i.e. regime transitions for different liquid viscosity, effect of microvesicularity, development and evolution of gas slugs); ii) to address the effects of conduit geometry on the flow dynamics by performing experiments on a new, dedicated rig (rectangular apparatus), reproducing the conditions of ascent of basaltic magma along a dike; iii) to carry out a systematic comparison between experimental results and field observations (i.e. both geophysical monitoring and eruptive products) at two end members: single cylindrical vent (Villarrica volcano) and multiple-vent system (Stromboli volcano); iv) to parameterize the main processes controlling flow regime stability and vesicularity of the magma column. We will monitor individual explosions using state-of-the-art techniques (i.e. seismic and acoustic arrays, IR camera, DOAS and radiometers) and collect fresh juvenile clasts. Physical properties and vesicle textures of the samples will be analysed and compared with experimental bubble distributions correlated to the natural system on the basis of geophysical monitoring. The success of the project is guaranteed by the unique expertise of the research team involved (including fluid dynamicists, geophysicists and volcanologists) and by the multidisciplinary strategies adopted (i.e. state-of-the-art experimental techniques, geophysical monitoring, field observations and data processing). As a result, this project represents a terrific opportunity to make substantial advances in our understanding of basaltic volcanism with obvious implications for risk reduction.