HR: 09:45h
AN: V11F-08    [Abstracts]
TI: The role of gas percolation in quiescent degassing of persistently active basaltic volcanoes
AU: * Burton, M
EM: burton@t.ingv.it
AF: INGV Catania, Piazza Roma, 2, Catania, 95123,
AU: Mader, H M
EM: H.M.Mader@bristol.ac.uk
AF: Bristol University, Wills Memorial Building Queens Road, Bristol, BS8 1RJ,
AU: Polacci, M
EM: polacci@ct.ingv.it
AF: INGV Catania, Piazza Roma, 2, Catania, 95123,
AB: Using constraints from literature data on the petrology and texture of erupted material from Stromboli and geochemical measurements of gas emissions together with a model of gas solubility we construct a conceptual model of quiescent degassing for this volcano. We find that within a pressure range between 100MPa and 50MPa (~3.6km and ~1.8km depth respectively) vesiculating magma ascending within the conduit becomes permeable to gas flow and a transition from closed- to open-system degassing takes place. Above the transition, gas, rich in the most insoluble gases, flows up through degassing magma, and thereby becomes enriched in more soluble gases during ascent to the surface. The final gas emission is therefore a superposition of gases released from magma above the percolation transition and gas that has evolved in closed-system below the transition. Steady-state gas release from Stromboli can only be sustained via magma circulation, driven by the density variation between ascending vesiculating magma and descending degassed magma. By balancing the buoyant force of ascending vesiculating magma against the viscous resistance produced by travelling through descending, degassed magma in a simple flow model we determine that a cylindrical conduit diameter of 2.5- 2.9m produces the magma mass flow rate of 575kgs-1, required to account for the observed quiescent SO2 gas flux on Stromboli of ~2.3kgs-1 (200td-1). Ascending magma accelerates during depressurization due to increasing vesicularity and requires ~8 hours to ascend from 200MPa (~7km depth) to the surface.
DE: 8430 Volcanic gases
DE: 8434 Magma migration and fragmentation
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting