Fragmentation mechanisms associated with explosive lava–water interactions in a lacustrine environment

Fitch, Erin P.; Fagents, S. A.; Thordarson, T.; Hamilton, C. W.

doi:10.1007/s00445-016-1087-3

Cited by 21 publications

(21 citation statements)

References 40 publications

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“…Lastly, lapilli-sized blocky clasts range in abundance from 1 to 25%, are more equant in shape, and have planar fracture faces that are typically covered in a fine layer of lacustrine sediment. The proportions of these three clast types do not vary significantly between the lower and upper bed-pair members within the same unit (Fitch et al 2017), nor are there significant variations in the abundance of fluidal versus mossy material between units. However, there is a distinct decrease in the abundance of blocky clasts with increasing stratigraphic height.…”

Section: Vertical Stratigraphy and Grain Sizementioning

confidence: 95%

“…However, there is a distinct decrease in the abundance of blocky clasts with increasing stratigraphic height. On average, juvenile clasts in the S layers have 63% fluidal, 27% mossy, and 9% blocky morphology (Fitch et al 2017) and are the most similar to the bed pairs in unit 1. Additionally, juvenile clasts within RTS2 commonly exhibit curvilinear fracture networks that occur preferentially on the lower surface of the clasts (Fig.…”

Section: Vertical Stratigraphy and Grain Sizementioning

confidence: 99%

“…This suggests that rootless MFCIs are far from being ideally efficient; the majority of the tephra generated from a rootless explosion, particularly in the upper bed-pair layers, may not have been directly involved with the MFCI, but rather was ejected from the upper lava column as a consequence of underlying explosions. Fitch et al (2017) explores this theme in more detail by investigating the fragmentation mechanisms associated with rootless explosions at Rauðhólar.…”

Section: Interpretation the Origin Of Bed-pair Layeringmentioning

confidence: 99%

“…Oxidation of the lava may play a minor role in generating this color, but the clasts are red primarily because they are coated with a thin film of red-to ochre-colored mud that is agglutinated onto their surfaces. Fitch et al (2017) provided a detailed examination of the componentry of the layers within the RTS2 layer, but results are discussed here for the lapilli-size fraction to aid in the overall characterization of the stratigraphy. The majority (61-94%) of the clasts within the bed-pair layers exhibit fluidal morphologies (Fig.…”

Section: Vertical Stratigraphy and Grain Sizementioning

confidence: 99%

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Rootless tephra stratigraphy and emplacement processes

et al. 2017

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Volcanic rootless cones are the products of thermohydraulic explosions involving rapid heat transfer from active lava (fuel) to external sources of water (coolant). Rootless eruptions are attributed to molten fuel-coolant interactions (MFCIs), but previous studies have not performed systematic investigations of rootless tephrostratigraphy and grain-size distributions to establish a baseline for evaluating relationships between environmental factors, MFCI efficiency, fragmentation, and patterns of tephra dispersal. This study examines a 13.55-m-thick vertical section through an archetypal rootless tephra sequence, which includes a rhythmic succession of 28 bed pairs. Each bed pair is interpreted to be the result of a discrete explosion cycle, with fine-grained basal material emplaced dominantly as tephra fall during an energetic opening phase, followed by the deposition of coarsergrained material mainly as ballistic ejecta during a weaker coda phase. Nine additional layers are interleaved throughout the stratigraphy and are interpreted to be dilute pyroclastic density current (PDC) deposits. Overall, the stratigraphy divides into four units: unit 1 contains the largest number of sediment-rich PDC deposits, units 2 and 3 are dominated by a rhythmic succession of bed pairs, and unit 4 includes welded layers. This pattern is consistent with a general decrease in MFCI efficiency due to the depletion of locally available coolant (i.e., groundwater or wet sediments). Changing conduit/ vent geometries, mixing conditions, coolant and melt temperatures, and/or coolant impurities may also have affected MFCI efficiency, but the rhythmic nature of the bed pairs implies a periodic explosion process, which can be explained by temporary increases in the water-to-lava mass ratio during cycles of groundwater recharge.

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Section: Vertical Stratigraphy and Grain Sizementioning

confidence: 95%

Section: Vertical Stratigraphy and Grain Sizementioning

confidence: 99%

Section: Interpretation the Origin Of Bed-pair Layeringmentioning

confidence: 99%

Section: Vertical Stratigraphy and Grain Sizementioning

confidence: 99%

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Rootless tephra stratigraphy and emplacement processes

et al. 2017

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“…In this study, since we aim to analyze the volcanic ash characteristics for each sample, it is necessary to classify ash into some category of shape. Previous studies have tried to classify volcanic ash particles into several categories: blocky 11 , 12 , 23 , vesicular 8 , 12 , 23 , mossy 11 , 23 , shard 8 , fluidal 11 , and rounded 23 , 24 . Considering these studies, we applied four typical basal shapes for volcanic ash particles: blocky, vesicular, elongated, and rounded (examples are shown in Fig.…”

Section: Preparation Of Particle Imagesmentioning

confidence: 99%

Classification of volcanic ash particles using a convolutional neural network and probability

Dake

Noguchi

Otsuki

et al. 2018

Sci Rep

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Analyses of volcanic ash are typically performed either by qualitatively classifying ash particles by eye or by quantitatively parameterizing its shape and texture. While complex shapes can be classified through qualitative analyses, the results are subjective due to the difficulty of categorizing complex shapes into a single class. Although quantitative analyses are objective, selection of shape parameters is required. Here, we applied a convolutional neural network (CNN) for the classification of volcanic ash. First, we defined four basal particle shapes (blocky, vesicular, elongated, rounded) generated by different eruption mechanisms (e.g., brittle fragmentation), and then trained the CNN using particles composed of only one basal shape. The CNN could recognize the basal shapes with over 90% accuracy. Using the trained network, we classified ash particles composed of multiple basal shapes based on the output of the network, which can be interpreted as a mixing ratio of the four basal shapes. Clustering of samples by the averaged probabilities and the intensity is consistent with the eruption type. The mixing ratio output by the CNN can be used to quantitatively classify complex shapes in nature without categorizing forcibly and without the need for shape parameters, which may lead to a new taxonomy.

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Assessing the Environmental Consequences of the Generation and Alteration of Mafic Volcaniclastic Deposits During Large Igneous Province Emplacement

Black¹,

Mittal²,

Lingo³

et al. 2021

Large Igneous Provinces

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Large igneous provinces (LIPs) famously host voluminous lava flows and large intrusive magma bodies that feed surface magmatism. However, they often also include substantial components of fragmental volcanic rocks. These fragmental rocks result from diverse processes including fire fountaining at fissures, phreatomagmatic interactions with subsurface fluids, and lava-water interactions. Pyroclastic fire fountaining and phreatomagmatic activity can generate buoyant eruption columns, modulating the altitude of gas injection. Both phreatomagmatic and lava-water activity can produce large volumes of permeable, glass-rich, mafic volcaniclastic material. These mafic volcaniclastic deposits (MVDs) are prone to reaction and alteration. Here, we review the role of mafic volcaniclastic rocks in LIPs, and consider the chemical fluxes and environmental consequences of mafic volcaniclastic alteration across a range of timescales. We suggest that release of phosphorus, nickel, and iron during emplacement and alteration of LIP mafic volcaniclastic deposits merits further investigation as a mechanism by which LIPs impact marine chemistry and productivity.

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Fragmentation mechanisms associated with explosive lava–water interactions in a lacustrine environment

Cited by 21 publications

References 40 publications

Rootless tephra stratigraphy and emplacement processes

Rootless tephra stratigraphy and emplacement processes

Classification of volcanic ash particles using a convolutional neural network and probability

Assessing the Environmental Consequences of the Generation and Alteration of Mafic Volcaniclastic Deposits During Large Igneous Province Emplacement

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