Effects of gas escape and crystallization on the complexity of conduit flow dynamics during lava dome eruptions

• Published in: Journal of Geophysical Research: Solid Earth Vol. 117; no. B8
• Main Authors: Kozono, T., Koyaguchi, T.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-08-2012; American Geophysical Union
• Subjects: conduit flow model; Crystallization; Earth sciences; Earth, ocean, space; effect of crystallization on viscosity; Exact sciences and technology; Flow rates; Geophysics; Lava; lava dome eruption; Lava domes; Magma; Permeability; Porosity; transition to explosive eruption; vertical and lateral gas escapes; Volcanic eruptions; Volcanic gases; Volcanoes; models; Critical value; domes; porosity; permeability; explosive eruptions; magmas; pressure; overpressure; friction; Complexity; Q; phenocrysts; dynamics; lava; viscosity; Feedback; crystallization; chemical composition; flow; Mass flow; volcanic gases
• ISSN: 0148-0227; 2169-9313; 2156-2202; 2169-9356
• DOI: 10.1029/2012JB009343

We investigated the coupled effects of gas escape and crystallization on the dynamics of lava dome eruptions using a one‐dimensional conduit flow model. The relationship between chamber pressure pch and mass flow rate q for steady conduit flow commonly has a regime of negative differential resistance (i.e., dpch/dq < 0), which causes a transition from lava dome to explosive eruption. Two positive‐feedback mechanisms that result in negative differential resistance have been identified. First, effective magma viscosity decreases with increasing q because of a delay of crystallization, leading to reduced viscous wall friction (feedback 1). Second, magma porosity increases with increasing q because of less efficient gas escape, leading to reduced gravitational load (feedback 2). For high‐phenocryst‐content magma (volume fraction >0.5), feedback 1 is the main mechanism that forms negative differential resistance. In this case, the transition from lava dome to explosive eruption occurs when the magma supply rate exceeds a fixed critical value. For low‐phenocryst‐content magma (volume fraction <0.5), feedback 2 plays a key role so that the transition is controlled by the permeability of the surrounding rocks; the critical magma supply rate remarkably decreases with decreasing permeability. Transition due to feedback 2 is associated with a change in the chemical composition of volcanic gas, a drastic increase in magma porosity from nearly 0 to greater than 0.8, and overpressure at a shallower level, which can be detected from geochemical and geophysical field observations.
Key Points
Effect of lateral gas escape on transition from lava dome to explosive eruption
Effect of crystallization on transition from lava dome to explosive eruption
Relative importance of gas escape and crystallization on conduit flow