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What factors control superficial lava dome explosivity?

Boudon G, Balcone-Boissard H, Villemant B, Morgan DJ - Sci Rep (2015)

Bottom Line: Superficial explosion of a growing lava dome may be promoted through porosity reduction caused by both vesicle flattening due to gas escape and syn-eruptive cristobalite precipitation.Explosive activity is thus more likely to occur at the onset of lava dome extrusion, in agreement with observations, as the likelihood of superficial lava dome explosions depends inversely on lava dome volume.This new result is of interest for the whole volcanological community and for risk management.

View Article: PubMed Central - PubMed

Affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, CNRS, F-75005, Paris, France.

ABSTRACT
Dome-forming eruption is a frequent eruptive style and a major hazard on numerous volcanoes worldwide. Lava domes are built by slow extrusion of degassed, viscous magma and may be destroyed by gravitational collapse or explosion. The triggering of lava dome explosions is poorly understood: here we propose a new model of superficial lava-dome explosivity based upon a textural and geochemical study (vesicularity, microcrystallinity, cristobalite distribution, residual water contents, crystal transit times) of clasts produced by key eruptions. Superficial explosion of a growing lava dome may be promoted through porosity reduction caused by both vesicle flattening due to gas escape and syn-eruptive cristobalite precipitation. Both processes generate an impermeable and rigid carapace allowing overpressurisation of the inner parts of the lava dome by the rapid input of vesiculated magma batches. The relative thickness of the cristobalite-rich carapace is an inverse function of the external lava dome surface area. Explosive activity is thus more likely to occur at the onset of lava dome extrusion, in agreement with observations, as the likelihood of superficial lava dome explosions depends inversely on lava dome volume. This new result is of interest for the whole volcanological community and for risk management.

No MeSH data available.


Related in: MedlinePlus

Evolution model for explosive (A) and ‚Äúnon-explosive‚ÄĚ (B) dome-forming eruptions.(A) In the case of explosive activity, the lava dome is small (less than 0.01‚ÄČkm3), possessing a rigid and impermeable silicified carapace formed through H4SiO4 flux. A small batch of vesiculated magma is isolated by local shear-fragmentation along the conduit wall, and causes a pressure build-up when intruding the growing lava dome. (B) In the case of a large lava dome (>to 0.01‚ÄČkm3) crystalline silica precipitation occurs pervasively and deep-seated fractures allow magma extrusion without overpressurization of the lava dome. The texture of the lava dome is in that case similar to the dense and silicified part of the explosive lava dome (Fig. 7A, photos 2 and 3). See text for further discussion. The figure was drawn by G. Boudon.
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f7: Evolution model for explosive (A) and ‚Äúnon-explosive‚ÄĚ (B) dome-forming eruptions.(A) In the case of explosive activity, the lava dome is small (less than 0.01‚ÄČkm3), possessing a rigid and impermeable silicified carapace formed through H4SiO4 flux. A small batch of vesiculated magma is isolated by local shear-fragmentation along the conduit wall, and causes a pressure build-up when intruding the growing lava dome. (B) In the case of a large lava dome (>to 0.01‚ÄČkm3) crystalline silica precipitation occurs pervasively and deep-seated fractures allow magma extrusion without overpressurization of the lava dome. The texture of the lava dome is in that case similar to the dense and silicified part of the explosive lava dome (Fig. 7A, photos 2 and 3). See text for further discussion. The figure was drawn by G. Boudon.

Mentions: i/the load of a small lava dome exerts a low pressure on its basement and the upper parts of the feeding conduit: the pressure buildup necessary to generate explosion is therefore low2137. Possibly, exsolved volatiles may migrate from ascending magma and concentrate within erupting magma beneath the impermeable carapace, leading to overpressurization37. The low proportion of vesiculated clasts (vesicularity >40%) in the D-PDC (Fig. 1) indicates that only a small batch of vesiculated magma is at the origin of the pressure buildup (Fig. 7A). The fraction of vesiculated clasts in lava dome explosion products is much lower in the May 8th 1902 eruption of Montagne Pelée (7%) than in the P1 eruption (15%) and Puy Chopine eruption (30%). These variations likely reflect variations in the depth of the explosion or the size of the lava dome. An explosion occurring within the lava dome requires less energy and likely a lower volume of vesiculated, less-degassed magma than an explosion occurring at the base of a lava dome or in the upper part of the feeding conduit. Lava dome growth is a self-defeating process: when the lava dome grows, the load progressively increases and the overpressure generated by exsolved gas becomes insufficient to overcome the load pressure and the lava dome strength to trigger an explosion39.


What factors control superficial lava dome explosivity?

Boudon G, Balcone-Boissard H, Villemant B, Morgan DJ - Sci Rep (2015)

Evolution model for explosive (A) and ‚Äúnon-explosive‚ÄĚ (B) dome-forming eruptions.(A) In the case of explosive activity, the lava dome is small (less than 0.01‚ÄČkm3), possessing a rigid and impermeable silicified carapace formed through H4SiO4 flux. A small batch of vesiculated magma is isolated by local shear-fragmentation along the conduit wall, and causes a pressure build-up when intruding the growing lava dome. (B) In the case of a large lava dome (>to 0.01‚ÄČkm3) crystalline silica precipitation occurs pervasively and deep-seated fractures allow magma extrusion without overpressurization of the lava dome. The texture of the lava dome is in that case similar to the dense and silicified part of the explosive lava dome (Fig. 7A, photos 2 and 3). See text for further discussion. The figure was drawn by G. Boudon.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588564&req=5

f7: Evolution model for explosive (A) and ‚Äúnon-explosive‚ÄĚ (B) dome-forming eruptions.(A) In the case of explosive activity, the lava dome is small (less than 0.01‚ÄČkm3), possessing a rigid and impermeable silicified carapace formed through H4SiO4 flux. A small batch of vesiculated magma is isolated by local shear-fragmentation along the conduit wall, and causes a pressure build-up when intruding the growing lava dome. (B) In the case of a large lava dome (>to 0.01‚ÄČkm3) crystalline silica precipitation occurs pervasively and deep-seated fractures allow magma extrusion without overpressurization of the lava dome. The texture of the lava dome is in that case similar to the dense and silicified part of the explosive lava dome (Fig. 7A, photos 2 and 3). See text for further discussion. The figure was drawn by G. Boudon.
Mentions: i/the load of a small lava dome exerts a low pressure on its basement and the upper parts of the feeding conduit: the pressure buildup necessary to generate explosion is therefore low2137. Possibly, exsolved volatiles may migrate from ascending magma and concentrate within erupting magma beneath the impermeable carapace, leading to overpressurization37. The low proportion of vesiculated clasts (vesicularity >40%) in the D-PDC (Fig. 1) indicates that only a small batch of vesiculated magma is at the origin of the pressure buildup (Fig. 7A). The fraction of vesiculated clasts in lava dome explosion products is much lower in the May 8th 1902 eruption of Montagne Pelée (7%) than in the P1 eruption (15%) and Puy Chopine eruption (30%). These variations likely reflect variations in the depth of the explosion or the size of the lava dome. An explosion occurring within the lava dome requires less energy and likely a lower volume of vesiculated, less-degassed magma than an explosion occurring at the base of a lava dome or in the upper part of the feeding conduit. Lava dome growth is a self-defeating process: when the lava dome grows, the load progressively increases and the overpressure generated by exsolved gas becomes insufficient to overcome the load pressure and the lava dome strength to trigger an explosion39.

Bottom Line: Superficial explosion of a growing lava dome may be promoted through porosity reduction caused by both vesicle flattening due to gas escape and syn-eruptive cristobalite precipitation.Explosive activity is thus more likely to occur at the onset of lava dome extrusion, in agreement with observations, as the likelihood of superficial lava dome explosions depends inversely on lava dome volume.This new result is of interest for the whole volcanological community and for risk management.

View Article: PubMed Central - PubMed

Affiliation: Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, CNRS, F-75005, Paris, France.

ABSTRACT
Dome-forming eruption is a frequent eruptive style and a major hazard on numerous volcanoes worldwide. Lava domes are built by slow extrusion of degassed, viscous magma and may be destroyed by gravitational collapse or explosion. The triggering of lava dome explosions is poorly understood: here we propose a new model of superficial lava-dome explosivity based upon a textural and geochemical study (vesicularity, microcrystallinity, cristobalite distribution, residual water contents, crystal transit times) of clasts produced by key eruptions. Superficial explosion of a growing lava dome may be promoted through porosity reduction caused by both vesicle flattening due to gas escape and syn-eruptive cristobalite precipitation. Both processes generate an impermeable and rigid carapace allowing overpressurisation of the inner parts of the lava dome by the rapid input of vesiculated magma batches. The relative thickness of the cristobalite-rich carapace is an inverse function of the external lava dome surface area. Explosive activity is thus more likely to occur at the onset of lava dome extrusion, in agreement with observations, as the likelihood of superficial lava dome explosions depends inversely on lava dome volume. This new result is of interest for the whole volcanological community and for risk management.

No MeSH data available.


Related in: MedlinePlus