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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

Magnetite textures at Montagne Pelée and Fe-Ti zoning pattern.Samples are from May, 8th, 1902 D-PDC (Montagne Pelée). (a) BSE image of an unexsolved magnetite (green line: TiO2 content profile in Fig. 5 B). The presence of a ring of melt inclusions helps to constrain the profile location. (b) Ti-diffusion profile modelling of (A), leading to a short timescale in vesiculated clast (~8 days). (c) Relative probability. Residence time data are from titanomagnetite grains recovered from dense and vesiculated pumices c1: Vesiculated clasts leading to “young” timescale (0–30 days) and c2: Dense clasts leading to “old” timescale (30+ days). The graphs show relative probability on an arbitrary vertical scale; populations are scaled by the number of crystals such that the area under the curve should equal unity and can be compared to individual crystal data in that graph. Uncertainties on individual diffusion data points (0.15 log units, 1-sigma) are Gaussian in log-time, meaning that they are asymmetric in linear time, as displayed. The height along the probability axis is scaled in order to conserve area, so that older crystals have a lower peak probability to match their wider uncertainty, and do not dominate signals when combining into population curves. Graph c1 shows the relative clustering of crystals from vesiculated pumices at short timescales. The single short-timescale crystal from dense pumice (c2) plots among the oldest of the crystals from the vesiculated pumice. We infer this to represent a relative increase in ascent velocity for the vesiculated pumice, which is also consistent with the pervasive alteration and exsolution of oxides in the dense pumice. Graphs c1 and c2 show that the older population of crystals in the vesiculated and dense products is effectively coincident and may reflect a similar origin and magma processing pathway. (d) BSE image of an exsolved magnetite.
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f5: Magnetite textures at Montagne Pelée and Fe-Ti zoning pattern.Samples are from May, 8th, 1902 D-PDC (Montagne Pelée). (a) BSE image of an unexsolved magnetite (green line: TiO2 content profile in Fig. 5 B). The presence of a ring of melt inclusions helps to constrain the profile location. (b) Ti-diffusion profile modelling of (A), leading to a short timescale in vesiculated clast (~8 days). (c) Relative probability. Residence time data are from titanomagnetite grains recovered from dense and vesiculated pumices c1: Vesiculated clasts leading to “young” timescale (0–30 days) and c2: Dense clasts leading to “old” timescale (30+ days). The graphs show relative probability on an arbitrary vertical scale; populations are scaled by the number of crystals such that the area under the curve should equal unity and can be compared to individual crystal data in that graph. Uncertainties on individual diffusion data points (0.15 log units, 1-sigma) are Gaussian in log-time, meaning that they are asymmetric in linear time, as displayed. The height along the probability axis is scaled in order to conserve area, so that older crystals have a lower peak probability to match their wider uncertainty, and do not dominate signals when combining into population curves. Graph c1 shows the relative clustering of crystals from vesiculated pumices at short timescales. The single short-timescale crystal from dense pumice (c2) plots among the oldest of the crystals from the vesiculated pumice. We infer this to represent a relative increase in ascent velocity for the vesiculated pumice, which is also consistent with the pervasive alteration and exsolution of oxides in the dense pumice. Graphs c1 and c2 show that the older population of crystals in the vesiculated and dense products is effectively coincident and may reflect a similar origin and magma processing pathway. (d) BSE image of an exsolved magnetite.

Mentions: Ti diffusion profiles in magnetite crystals from Montagne Pelée (May, 8th 1902 event) have been studied following the method developed on pyroxenes by Morgan and collaborators24. This eruptive event has been chosen to estimate the transit time of magma in the conduit. The textural characteristics of the magnetite crystals depend on the vesicularity of host clasts (Fig. 5a,d). In vesiculated clasts, magnetites display a normal zoning with Ti-rich cores and Ti-poor rims that are in equilibrium with the residual melt (Fig. 5a,b). In dense clasts, two types of textures are evidenced. In some dense, degassed clasts, only few magnetites exhibit the same textural features as vesiculated clasts (~15%); but most crystals are exsolved (Fig. 5d) indicating that they have re-equilibrated at temperatures below the solvus, and likely in oxidizing conditions25. In other dense clasts all magnetites are exsolved, indicating a sufficiently long storage time under the appropriate conditions to allow complete exsolution. From over 100 crystals of magnetite separated in vesiculated fragments, 13 diffusion profiles were usable, while over more than 150 separates in dense fragments only three profiles were usable.


What factors control superficial lava dome explosivity?

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

Magnetite textures at Montagne Pelée and Fe-Ti zoning pattern.Samples are from May, 8th, 1902 D-PDC (Montagne Pelée). (a) BSE image of an unexsolved magnetite (green line: TiO2 content profile in Fig. 5 B). The presence of a ring of melt inclusions helps to constrain the profile location. (b) Ti-diffusion profile modelling of (A), leading to a short timescale in vesiculated clast (~8 days). (c) Relative probability. Residence time data are from titanomagnetite grains recovered from dense and vesiculated pumices c1: Vesiculated clasts leading to “young” timescale (0–30 days) and c2: Dense clasts leading to “old” timescale (30+ days). The graphs show relative probability on an arbitrary vertical scale; populations are scaled by the number of crystals such that the area under the curve should equal unity and can be compared to individual crystal data in that graph. Uncertainties on individual diffusion data points (0.15 log units, 1-sigma) are Gaussian in log-time, meaning that they are asymmetric in linear time, as displayed. The height along the probability axis is scaled in order to conserve area, so that older crystals have a lower peak probability to match their wider uncertainty, and do not dominate signals when combining into population curves. Graph c1 shows the relative clustering of crystals from vesiculated pumices at short timescales. The single short-timescale crystal from dense pumice (c2) plots among the oldest of the crystals from the vesiculated pumice. We infer this to represent a relative increase in ascent velocity for the vesiculated pumice, which is also consistent with the pervasive alteration and exsolution of oxides in the dense pumice. Graphs c1 and c2 show that the older population of crystals in the vesiculated and dense products is effectively coincident and may reflect a similar origin and magma processing pathway. (d) BSE image of an exsolved magnetite.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Magnetite textures at Montagne Pelée and Fe-Ti zoning pattern.Samples are from May, 8th, 1902 D-PDC (Montagne Pelée). (a) BSE image of an unexsolved magnetite (green line: TiO2 content profile in Fig. 5 B). The presence of a ring of melt inclusions helps to constrain the profile location. (b) Ti-diffusion profile modelling of (A), leading to a short timescale in vesiculated clast (~8 days). (c) Relative probability. Residence time data are from titanomagnetite grains recovered from dense and vesiculated pumices c1: Vesiculated clasts leading to “young” timescale (0–30 days) and c2: Dense clasts leading to “old” timescale (30+ days). The graphs show relative probability on an arbitrary vertical scale; populations are scaled by the number of crystals such that the area under the curve should equal unity and can be compared to individual crystal data in that graph. Uncertainties on individual diffusion data points (0.15 log units, 1-sigma) are Gaussian in log-time, meaning that they are asymmetric in linear time, as displayed. The height along the probability axis is scaled in order to conserve area, so that older crystals have a lower peak probability to match their wider uncertainty, and do not dominate signals when combining into population curves. Graph c1 shows the relative clustering of crystals from vesiculated pumices at short timescales. The single short-timescale crystal from dense pumice (c2) plots among the oldest of the crystals from the vesiculated pumice. We infer this to represent a relative increase in ascent velocity for the vesiculated pumice, which is also consistent with the pervasive alteration and exsolution of oxides in the dense pumice. Graphs c1 and c2 show that the older population of crystals in the vesiculated and dense products is effectively coincident and may reflect a similar origin and magma processing pathway. (d) BSE image of an exsolved magnetite.
Mentions: Ti diffusion profiles in magnetite crystals from Montagne Pelée (May, 8th 1902 event) have been studied following the method developed on pyroxenes by Morgan and collaborators24. This eruptive event has been chosen to estimate the transit time of magma in the conduit. The textural characteristics of the magnetite crystals depend on the vesicularity of host clasts (Fig. 5a,d). In vesiculated clasts, magnetites display a normal zoning with Ti-rich cores and Ti-poor rims that are in equilibrium with the residual melt (Fig. 5a,b). In dense clasts, two types of textures are evidenced. In some dense, degassed clasts, only few magnetites exhibit the same textural features as vesiculated clasts (~15%); but most crystals are exsolved (Fig. 5d) indicating that they have re-equilibrated at temperatures below the solvus, and likely in oxidizing conditions25. In other dense clasts all magnetites are exsolved, indicating a sufficiently long storage time under the appropriate conditions to allow complete exsolution. From over 100 crystals of magnetite separated in vesiculated fragments, 13 diffusion profiles were usable, while over more than 150 separates in dense fragments only three profiles were usable.

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