the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Dec 2025
Experimental analysis of Taylor bubble regimes using kymography: a tool for understanding bubble ascent dynamics in open-vent volcanic conduits
Abstract. Taylor bubbles, or gas slugs, are elongated gas pockets that drive discrete and cyclic Strombolian explosions. To understand the surface dynamics of such eruptions, it is essential to first characterize the subsurface flow behaviour within the shallow (<1 km) volcanic plumbing system. This can be achieved experimentally by simulating Taylor bubble flow under conditions that are mathematically scalable to volcanic conduit settings. This paper presents a novel application of kymography – an existing visual analysis technique – for measuring isolated or continuous Taylor bubble flow experimentally in vertical cylindrical pipes. Kymographs condense thousands of frames of experimental footage into a single space-time image, enabling efficient analysis of flow dynamics. The method utilises open-source software (ImageJ), affordable experimental equipment, and straightforward calibration, making it both cost-effective and widely accessible. Here, we illustrate the value of incorporating kymography to simplify and enhance data retrieval from complex two-phase fluid problems which provide a rigorous first order understanding of the flow processes governing surface eruption dynamics exhibited by open-vent basaltic volcanoes. We show that kymography serves as a valuable and effective visual analysis tool for the experimental measurement of gas volume fraction, gas and liquid slug velocities, bubble length and diameter, falling film thickness, bubble and coalescence event counts, and to indicate steady state ascent. In a volcanic conduit, these parameters have important implications for flow stability, interaction dynamics, overpressure development, and the volume of gas released at burst, which ultimately aids our ability to understand and predict eruption style, periodicity, repose, and explosivity level.
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Status: open (until 30 Jan 2026)
- RC1: 'Comment on egusphere-2025-3621', Anonymous Referee #1, 05 Jan 2026 reply
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RC2: 'Comment on egusphere-2025-3621', Anonymous Referee #2, 08 Jan 2026
reply
The manuscript entitled "Experimental analysis of Taylor bubble regimes using kymography: a tool for understanding bubble ascent dynamics in open-vent volcanic conduits" is well written and fits the Geoscientific Instrumentation, Methods and Data Systems scope.
This paper presents no new concept but rather a proof of applicability of an existing tool, the kymography, to the given problem of Taylor bubbles in volcanic regimes.
The paper is well structured and results are relatively clear.
The experimental conditions are well described, and the data obtained are provided, which gives a good reproducibility.
However, some points (listed below) could improve the overall quality of the present manuscript.
MINOR POINTS:- More discussions about the correlation and relationship between variables should be added.
- From the title, abstract and conclusion, it is claimed that these experiments help to understand dynamics in volcanoes.
But it is not so clear how.
What does these experiments bring to the actual understanding ? This should be clarified.- Since the tube is cylindrical, there can be optic effects, in the measurement.
These effects are taken into account, but only explained in the appendix 4, which is regrettable, since the reader needs this information to fully understand.
Appendix 4 could benefit from an optical sketch.- Table 1 should include dimensionless numbers studied, plus advantage and drawbacks of the techniques used.
This could help to emphasize the contribution here.
It could also include an optical flow input.- Dimensionless numbers definitions used should be explicit because their definitions are not always unique.
For example, the Reynolds number, Re, is taken around a characteristic bubble or in the Poiseuille flow ?
And explain why they are not fitting with the volcano numbers ? (from Table 2)
EDITION POINTS:- In mathematical variables, the subscript index should be in Roman style when they are not referring to another variable (but to a word or abbreviation, etc.).
- The bibliographic citation (author name + year) should be homogenized (using italic style everywhere for example).
- In Figure 2, the variable Lb is not consistent in the way it is measured between the top and the bottom of the figure.
- In Figure 3, caption and image not on the same page, which does not help the reading.
- Adding a figure about the Taylor bubbles in the volcano plumbering could help the pedagogy of the introduction.
Citation: https://doi.org/10.5194/egusphere-2025-3621-RC2
Data sets
Dataset for Calleja et al. "Experimental analysis of Taylor bubble regimes using kymography" Hannah Calleja https://doi.org/10.5281/zenodo.16037059
Model code and software
distortion_code [for Calleja et al. "Experimental analysis of Taylor bubble regimes using kymography"] Eric C. P Breard https://doi.org/10.5281/zenodo.16038113
GVF-prediction_code [for Calleja et al. "Experimental analysis of Taylor bubble regimes using kymography"] Eric C. P. Breard https://doi.org/10.5281/zenodo.16109361
Video supplement
Sample experiment footage [for Calleja et al. "Experimental analysis of Taylor bubble regimes using kymography"] Hannah Calleja https://doi.org/10.5281/zenodo.16040076
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General comments
The manuscript is intended to be an illustration of the value of kymography to analyse Taylor bubbles flows, which are extensively studied in volcanology, in transparent pipes. As such, this work is clearly in the scope of Geoscientific Instrumentation, Methods and Data Systems. Although the first section of the text (1.1) discusses mainly the importance of characterising the dynamics of bubbles ascending volcanic conduits for understanding the transition from effusive to effusive volcanic activity, the dimensionless parameters of the flows studied in the article are not all comparable with volcanic conditions ; the paragraph 2.1 adresses this issue, explaining that water was included in the study because of its prevalence in the literature, which seems relevant. The methodology used to generate the kymographs is thoroughly detailed, as well as the computations done to extract the key flow parameters from the kymographs. The errors caused by the manual pixel selection and by the distortion induced by the camera lens are quantified, and the correction of the refraction at the tube boundaries is well-explained in Appendix 5. It should be stressed that the raw kymographs as well as the scripts mentionned in the Appendix 4 and 6 are provided by the authors, which constitutes good research practice. As a conclusion, i find the study interesting and serious enough to be accepted, even though i have a few remarks and suggestions.
Specific comments
- On figure 4 : the differences between manual evaluation and kymograph measurements are more important with water than with glycerol-water, which is not really mentioned in the paragraph 2.4. The same remarks applies to figures 5 and 6.
- In 2.4 (l 291), it would be better to express the margin as a relative error rather than an absolute one.
Technical corrections
- Appendix 4 : Should the angle on the left-hand member of equation 4 not be theta_PVC rather than theta_air ?
- Figure 3 : The kymographs in (A) are a bit overloaded with captions, which hinders readibility. For instance, it may not be necessary to draw all the dashed lines in the first kymograph.
- Appendix figure 2 Different names should be given to figures B (theorical) and B (experimental) for the sake of clarity.