Surface degassing and modifications to vesicle size distributions in active basalt flows

Cashman, Katharine V.; Mangan, Margaret T.; Newman, Sally

doi:10.1016/0377-0273(94)00015-8

Cited by 139 publications

(67 citation statements)

References 43 publications

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“…He attributed these to significant lava density increases during emplacement. These and other studies [e.g., Einarsson et al, 1949;Cashman et al, 1994] suggest that differences between erupted and emplaced volumes of lava may be quite common in basaltic and basaltic andesite flows. Malin [1980] …”

Section: Introductionsupporting

confidence: 55%

Influence of volatile loss on thickness and density profiles of active basaltic flow lobes

Baloga¹,

Glaze²,

Peitersen³

et al. 2001

J. Geophys. Res.

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Abstract. A bulk density increase due to degassing during emplacement may have a significant influence on the thickness of a lava flow and the rate at which it advances. We present a theoretical model of a lava flow that loses enough volatiles to cause density changes along the path of the flow. We assume that the flow is emplaced as a single, isolated unit and the bulk rheology (e.g., viscosity) is a function of distance from the vent. This type of model is applicable to solitary lobes of basaltic aa and isolated sheets of pahoehoe that advance as a fluid continuum with bulk lava density changes as a function of distance along the flow path. Equations for the flow thickness and the bulk density profiles are derived from mass and volume conservation. Formulas are tabulated for thickness and density profiles for various combinations of flow rates, rheologic changes, and degassing rate functions. We also tabulate formulas for estimating parameters associated with the form and rate of degassing from field data. The Mauna Loa 1984 "1 flow" is a typical example of a flow showing evidence of a bulk density increase and is used to estimate the model parameters. Thickness and density profiles are then computed for a range of plausible lava densities, two different rate functions for the loss of volatiles, and two different models of viscosity change. Results indicate that the thickness profile of a lava flow can be significantly affected when there is a large difference between the density at the vent and at the flow front. For relatively high rates of degassing, the flow profile has a maximum thickness located progressively closer to the vent as the rate of degassing increases. For depth-dependent degassing, an increase in viscosity acts to thicken the flow, which increases the rate of degassing, thus mitigating the thickening influence of the increasing viscosity. Degassing while a flow is active can increase the duration of emplacement by as much as 60%. We find that the flow thickness profiles are sensitive to the choice of flow rate and the initial density, regardless of the form of the degassing function. The nature of the flow rate can significantly affect the shape of the profile as well as the flow front thickness. When the rate of volatile loss depends on the flow thickness, the density profile depends explicitly on the way the rheology changes along the flow path. In all cases, density increases during emplacement counter the tendency of a flow to thicken due to increases in viscosity or resistance to flow with distance. Thus the parameters that define the rate of degassing, and the consequent density change along the path of a flow, emerge as important variables for a quantitative understanding of flow emplacement.

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Section: Introductionsupporting

confidence: 55%

Influence of volatile loss on thickness and density profiles of active basaltic flow lobes

Baloga¹,

Glaze²,

Peitersen³

et al. 2001

J. Geophys. Res.

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“…Between eruptions ( Figure 7a) the conduit is occupied by a static magma column, perhaps capped by fallback or collapsed vent walls near the surface (not shown). Because of its low viscosity, Kilauean magma that is exposed to atmospheric pressure loses most of its gas in a few hours [Cashman et al, 1994] and should be mostly degassed in the uppermost few hundred meters between eruptions. Its density would be roughly 2650 kg m -3 (the density of unvesiculated magma) (Table 1) (Figure 7b, arrows).…”

Section: Evolution Of Conduit Pressure During An Eruptionmentioning

confidence: 99%

“…The pumice fragments are remarkable for their abundant, very fine textured vesicles (Figure 4). Quantitative studies at Kilauea [e.g., Mangan et al, 1993;Cashman et al, 1994;Mangan and Cashman, 1996] show that highly vesiculated, fine-textured pumice is produced only in lava fountains which involve sustained, high rates of magma flux. This point was also recognized by Dvorak [1992], though he made no…”

Section: Introductionmentioning

confidence: 99%

Evidence for water influx from a caldera lake during the explosive hydromagmatic eruption of 1790, Kilauea volcano, Hawaii

Mastin¹

1997

J. Geophys. Res.

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Abstract. In 1790 a major hydromagmatic eruption at the summit of Kilauea volcano, Hawaii, deposited up to 10 m of pyroclastic fall and surge deposits and killed several dozen Hawaiian natives who were crossing the island. Previous studies have hypothesized that the explosivity of this eruption was due to the influx of groundwater into the conduit and mixing of the groundwater with ascending magma. This study proposes that surface water, not groundwater, was the agent responsible for the explosiveness of the eruption. That is, a lake or pond may have existed in the caldera in 1790 and explosions may have taken place when magma ascended into the lake from below. That assertion is based on two lines of evidence: (1) high vesicularity (averaging 73% of more than 3000 lapilli) and high vesicle number density (105-107 cm -3 melt) of pumice clasts suggest that some phases of the eruption involved vigorous, sustained magma ascent; and (2) numerical calculations suggest that under most circumstances, hydrostatic pressure would not be sufficient to drive water into the eruptive conduit during vigorous magma ascent unless the water table were above the ground surface. These results are supported by historical data on the rate of infilling of the caldera floor during the early 1800s. When extrapolated back to 1790, they suggest that the caldera floor was below the water table.

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“…Textural studies of the vesicles in volcanic products provide information on the conditions of 410 bubble nucleation and growth in magmas (which usually requires quantifying a timescale for 411 bubble growth independently), which may include quantifying decompression rates and 412 mechanisms of magma fragmentation (Cashman and Mangan, 1994 …”

mentioning

confidence: 99%

Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Edmonds

Humphreys

Hauri

et al. 2014

Memoirs

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Citation for published item:idmondsD wF nd rumphreysD wFgFF nd ruriD iF nd rerdD F nd dgeD qF nd wsonD rF nd veddenD F nd lilD wF nd frlyD tF nd eiuppD eF nd ghristopherD F nd qiudieD qF nd quidD F @PHIRA 9reEeruptive vpour nd its role in ontrolling eruption style nd longevity t oufri ere rills olnoF9D wemoirsFD QW F ppF PWIEQISF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Schmidt and Poli, 1999). The generation of mafic magmas in the "hot 52 zone" at the base of the arc crust is fundamentally controlled by the H 2 O content of the melts, 53 which act to "flux" the amphibolite crust and cause assimilation (Annen et al,. 2006). In 54 shallow storage areas, the exsolved fluid content of stored magma directly influences the 55 compressibility and hence response of the magma body to changes in pressure or volume, 56 ultimately determining magma ascent rates and eruption style, as well as eruption duration 57 and size (Huppert and Woods, 2002). The rate of crystallisation of magma in crustal 58 reservoirs is influenced by the opposing effects of fluxing by CO 2 -rich gases from depth, 59 which act to "freeze" the magma (Blundy et al., 2010), and new batches of incoming hot, 60 volatile-rich magma, which act to "defrost" it, by heating and transferring H 2 O-rich fluids 61 (e.g. Bachmann and Bergantz, 2006). Sulphur partitions into this fluid (e.g. Scaillet et al., 62 1998;Zajacz et al., 2012), further enhancing the proportion of vapour coexisting with the 63 magma prior to the eruption, and acting as a convenient tracer to measure in volcanic gases 64 (e.g. Gerlach et al., 2008). In the conduit, transitions between lava dome building and 65 explosive Vulcanian activity are controlled by finely-balanced feedbacks involving the 66 development of permeability during degassing, and the increase in viscosity and consequent 67 retardation of bubble growth caused by crystallisation and H 2 O exsolution from the melt 68 (Melnik and Sparks, 1999;Sparks et al., 2000;Melnik and Sparks, 2002; Clarke et al., 2007). 69 CarmichaelThe arc magma system is complex; petrological and geochemical evidence points to the 70 erupted porphyritic andesite being a hybrid, the result of perhaps countless recharge events by 71 internal energy associated with dissolved volatiles can be released into the magma chamber, 87 and this is a mechanism for inducing complex eruption cycles on long timescales for volatile-88 rich magmas (Huppert and Woods, 2002). One mechanism for this is the presence of a large 8...

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Surface degassing and modifications to vesicle size distributions in active basalt flows

Cited by 139 publications

References 43 publications

Influence of volatile loss on thickness and density profiles of active basaltic flow lobes

Influence of volatile loss on thickness and density profiles of active basaltic flow lobes

Evidence for water influx from a caldera lake during the explosive hydromagmatic eruption of 1790, Kilauea volcano, Hawaii

Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

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