the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Jul 2025
Volcanic plume height during the 2021 Tajogaite eruption (La Palma) from two complementary monitoring methods. Implications for satellite-based products
Abstract. Volcanic emissions from the Tajogaite volcano, located on the Cumbre Vieja edifice on the island of La Palma (Canary Islands, Spain), caused significant public health and aviation disruptions throughout the volcanic event (19 September – 13 December 2021, officially declared over on 25 December). The Instituto Geográfico Nacional (IGN), the authority responsible for volcano surveillance in Spain, implemented extensive operational monitoring to track volcanic activity and to provide a robust estimation of the volcanic plume height using a video-surveillance network. In parallel, the State Meteorological Agency of Spain (AEMET), in collaboration with other members of ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) in Spain, in collaboration with other institutions, carried out an unprecedented instrumental deployment to assess the atmospheric composition impacts of this volcanic event. This effort included a network of aerosol profilers surrounding the volcano. A total of four profiling instruments were installed on La Palma: one MPL-4B lidar and three ceilometers. Additionally, a pre-existing Raman lidar on the island contributed valuable data to this study.
In this study, the eruptive process was characterised in terms of the altitude of the dispersive volcanic plume (hd), measured by both IGN and AEMET-ACTRIS, and the altitude of the eruptive column (hec), measured by IGN. Modulating factors such as seismicity and meteorological conditions were also analysed. The consistency between the two independent and complementary datasets (hd,IGN and hd,AEMET) was assessed throughout the eruption (mean difference of 258.6 m).
Our results confirmed the existence of three distinct eruptive phases, encompassing a range of styles from Strombolian explosive to effusive activity. While these phases have been characterised in previous studies, the results of the present work provide complementary information and novel insights from a different scientific perspective, which may be of use in future volcanic crises and will be applied to operational surveillance during such events.
A subsequent comparison of hd,AEMET with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol layer height product (ALHCALIOP) revealed a systematic underestimation by the satellite product, with a mean difference of 392.2 m.
Finally, the impact of using hec in estimating SO2 emissions from the NASA MSVOLSO2L4 satellite-based product was evaluated. When a fixed (standard) plume altitude of 8 km was used instead of the observed hec, the total SO2 mass was significantly underestimated by an average of 56.2 %, and by up to 84.7 %. These findings underscore the importance of accurately determining the volcanic plume height when deriving SO2 emissions from satellite data.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-3164', Anonymous Referee #1, 18 Aug 2025
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RC2: 'Comment on egusphere-2025-3164', Anonymous Referee #2, 09 Oct 2025
Scientific significance: Excellent
The study provides a significant and original contribution. The combined use of IAC-IGN video-based height retrievals, ACTRIS–AEMET ground lidars, and satellite products provides a comprehensive dataset unprecedented for the 2021 Tajogaite eruption. The documented influence of plume height on SO₂ mass estimation, with up to an 85% reduction in bias upon correction, holds considerable operational and scientifically significant.
Scientific quality. Excellent
The methodology is rigorous and thoroughly described. The analysis employs independent instruments and cross-validation techniques, thereby ensuring robustness. The primary limitation lies in the absence of detailed uncertainty propagation and supplementary statistical metrics (e.g., RMSE, correlation) between datasets — these are minor issues but prevent achieving an optimal score. The discussion is well-balanced, and references are comprehensive.
Presentation quality: Good
The manuscript exhibits a well-organized structure, with fluent English usage. The figures are informative and visually clear; however, enhancements such as clarification, inclusion of error bars, summary statistics, and a brief note regarding algorithm parameters could be beneficial. These suggestions pertain to minor presentation refinements rather than scientific shortcomings. Additionally, the inclusion of other pertinent references from previous works might have been advantageous.
General Comments:
This manuscript offers a thoroughly conducted and significant investigation into the characterization of plume heights during the 2021 Tajogaite (La Palma) eruption, utilizing complementary datasets from IGN video observations, AEMET–ACTRIS aerosol profilers, and satellite instruments. The study emphasizes the essential role of precise, real-time plume height measurements in ensuring reliable satellite retrievals of volcanic emissions and establishes a valuable framework for future volcanic crisis management.
The primary enhancements required are minor, including the incorporation of fundamental statistical indicators such as RMSE and correlation for the AEMET-IGN comparison (see Fig. 4), a concise sensitivity analysis of CALIOP results, clarification or correction within graphical regions, and the explicit delineation of uncertainty ranges.
The manuscript is clearly written, well organized, and enhanced with high-quality figures. It makes a significant and original contribution to atmospheric measurement science. I recommend acceptance after minor revisions.
Technical Comments:
Regarding Figure 4: This plot would substantially benefit from the inclusion of a descriptive table that provides a comprehensive statistical analysis. This should include correlation coefficients between the AEMET-ACTRIS and IGN datasets for dispersive plume heights (h_d). Additionally, such a table could quantify differences stratified by AEMET instrument type in comparison to IGN measurements, thereby enhancing the interpretability of inter-method consistency. Notably, multiple data points appear for the same day and source (particularly for h_d, IGN), which may introduce visual clutter; consolidating these into daily aggregates—such as means and standard deviations, where applicable—could improve clarity. Nonetheless, the table already presents a synthesized view, as it is effectively summarized in Figure 5a through daily averaged values by source. The proposed statistical table would thus serve as a valuable complement for a rigorous intercomparison.
Regarding Figure 6: The discussion of wind direction analysis in lines 473–479 lacks sufficient clarity, particularly in elucidating the methodological basis for the wind rose construction. Intermediate directional sectors (intercardinal headings) between principal cardinal points (N–E–S–W) are incorrectly labeled; for instance, the sector between south and west should be designated SW, with analogous corrections for other quadrants. The boundary between W and SW, corresponding to 247.5° (referenced to 0° as north) as WSW, exemplifies this issue. Conventionally, wind roses depict the direction from which the wind originates (provenance), rather than toward which it blows. I recommend redrawing the wind rose with explicit labeling of the directional convention (e.g., "wind from" or "wind toward") to avoid ambiguity. Furthermore, while Figure 1 accurately positions the Tazacorte (west) and Fuencaliente (south) stations relative to the island, the text and Figure 6 introduce confusion in their spatial referencing, which should be reconciled for consistency.
Regarding Figure 8 and section 4.4: the data points representing the eruptive column height (h_ec) are indicated by blue circles, not orange as might be inferred from the caption or legend—please verify and rectify this for accuracy. Additionally, the use of the color “red” may be preferable to “light red.” The SO₂ emission rates are expressed in kilotonnes, yet they seem to pertain to daily fluxes (kt day⁻¹); explicitly stating the temporal averaging (e.g., daily emission rates [kt·day⁻¹]) in the axis labels and accompanying text would prevent misinterpretation. Furthermore, it is advisable to review the bibliography to include any prior studies that report similar underestimations of satellite-derived emission rates during volcanic eruptions (e.g., via UV hyperspectral retrievals). If applicable, incorporate references to complementary ground-based or alternative methodological estimates of SO₂ emission rates (kt day⁻¹), such as differential optical absorption spectroscopy (DOAS) or flux tower measurements related to Tajogaite, in order to provide a more comprehensive contextualization of the findings.
I recommend reviewing the figure/table captions alongside their narrative in the text to ensure complete consistency.
Citation: https://doi.org/10.5194/egusphere-2025-3164-RC2
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GENERAL COMMENTS
The study by Barreto et al. compares estimates of plume height during the Tajogaite eruption in 2021 derived from two independent approaches: one based on video-surveillance cameras and the other on ground-based remote-sensing profiling instruments. The temporal evolution of plume height is further examined in relation to ancillary measurements. The implications of plume height overestimation for satellite-based SO2 retrieval algorithms are considered, and plume altitude estimations from the surface are compared with CALIOP observations.
The manuscript presents a substantial amount of material, and the overall analyses appear solid and convincing. However, the paper lacks a clear articulation of the specific research questions, which makes it somewhat difficult to follow and gives the impression that the central thread of the study is not fully established. In addition, a more detailed discussion of the uncertainties associated with each technique would strengthen the comparison of results. Overall, I would recommend publication once these issues have been adequately addressed.
SPECIFIC COMMENTS
1. Research questions – Please state the main research questions explicitly in the Introduction, and organise the manuscript accordingly. In addition, highlight the novel aspects of the study in relation to the abundant literature on the same eruption already cited in the bibliography.
2. Algorithm consistency – If I understand correctly, different algorithms were used to estimate plume height from profiling instruments. Why was a single, uniform algorithm not applied, which would have enabled a more consistent comparison?
3. Uncertainty – A thorough discussion of the uncertainties associated with plume altitude retrievals from the different methods is essential before drawing comparisons. Without this, the statement that the results are "highly consistent" (lines 393–394) is difficult to justify. Moreover, it is unclear whether plume height is always defined as the altitude of the plume top, or alternatively as the altitude corresponding to a maximum in the signal. Please clarify.
4. Modulating factors – The discussion of the relationships between plume height and ancillary variables is predominantly qualitative. Are there any models, even empirical ones, that could provide more quantitative estimates of plume altitude as a function of the parameters considered?
5. CALIOP – An average overpass distance of 61.7 km appears rather large for direct comparison with CALIOP. How far is the plume expected to be horizontally transported under the observed conditions? Furthermore, what are the results of the CALIOP aerosol typing? To which aerosol class is the layer attributed?
6. Emissions – Is there any means of determining whether the new estimates of SO2 emissions based on measured plume altitude provide an improvement over the default values?
7. Terminology – The comparison of methods is presented largely in terms of institutions (i.e. IGN vs AEMET–ACTRIS). While this may be relevant for the authors, readers are likely to be more interested in the distinction between techniques, namely video-surveillance cameras versus ground-based profiling instruments. I would recommend revising the subscripts of the variable names accordingly.
TECHNICAL REMARKS