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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RC1: 'Comment on egusphere-2025-3164', Anonymous Referee #1, 18 Aug 2025
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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
- Abstract – Please state why plume height determination is important already in the abstract.
- Line 2 – Replace "volcanic event" with "eruption" on first mention.
- Lines 6–7 – The phrase "in collaboration" is repeated.
- Line 17 – The phrase "different scientific perspective" is vague. Please clarify what the different perspective entails.
- Lines 22–25 – Are SO2 and the aerosol vertical profiles expected to be similar in proximity to the source? Please, explain the reason in the manuscript.
- Introduction – The section is rather wordy. Some paragraphs could be shortened, retaining only information directly relevant to the scope of the manuscript.
- Line 38 – The expression "conversion process from primary to secondary aerosols" is unclear. The preceding text refers to gas-to-aerosol conversion, not aerosol-to-aerosol processes. Please clarify.
- Line 44 – "significantly longer": is this due to particle size, or to chemical composition? Please specify.
- Line 47 – Bibliographic references are required.
- Lines 83–91 – Given the large number of existing studies, the novelty of this work should be highlighted more clearly. The statement that "this study aims to present the unprecedented instrumental coverage..." is too generic. This would be the ideal point to explicitly state the scientific questions that remain open and will be answered here.
- Line 106 – Rather than emphasising the different networks, it may be more informative to highlight the differences between techniques, as noted above.
- Line 113 – Consider starting the sentence with "The eruption began...".
- Lines 118–120 – As this is key information, it could also be included in the abstract.
- Lines 121–126 – These lines are only loosely connected to the paper's focus and could be condensed.
- Lines 127–131 – This paragraph might be better placed earlier in the event description.
- Section 3.1 – Please clarify whether the reported technique was developed specifically for this study or if it has been described previously.
- Figure 1 – It may be useful to explain why the grid is slightly tilted relative to the figure margins.
- Figure 2 caption – “LA” → “La”.
- Line 191 – "in record time" is too informal. Instead, state the precise number of days.
- Section 3.2 – Please homogenise the terminology for instruments (e.g. ceilometers vs lidar ceilometers) or explain why you keep the naming different. Note that ACTRIS currently uses "Automatic low-power lidars and ceilometers (ALCs)" or, more generally, "Automatic lidar ceilometers (ALCs)".
- Line 272 – As vertical resolution is an instrument characteristic, this should be mentioned directly after "backscattered signal" in the same sentence.
- Lines 274–277 – Were the profiles corrected for overlap? Please clarify.
- Line 282 – "sharp gradients" – do you refer specifically to negative gradients? Please specify.
- Lines 292–293 – Why is this algorithm different? Was it validated against the others?
- Line 292 – The "temporal evolution of attenuated backscatter profiles" does not appear to require retrievals. Are the authors instead referring to the identification of aerosol layer tops?
- Line 306 – Wording suggestion: "... pre-calibrated at the Vaisala facilities using liquid water clouds...".
- Line 311 – Why are only six cases considered? Please explain.
- Lines 357–362 – As this mission ended on 1 August 2023, this paragraph should be written in the past tense.
- Line 364 – The term "loading" is ambiguous. Does it refer to emissions or concentrations? Similarly, "budgets" (line 384) is unclear. Lines 373–375 could be moved earlier to clarify the product description.
- Section 4.1 – As noted above, it may be clearer to separate the discussion by technique rather than by research group.
- Figure 4 – Given the evident variability in plume height, short-term fluctuations (line 389) should be discussed in greater detail. To better assess the agreement/differences in altitude estimates, consider splitting Figure 4 into two or more panels covering different time intervals.
- Line 396 – Please specify when the maximum difference occurred. Similarly, indicate when the minimum occurred (line 397).
- Line 401 – "limited number of measurements": please restate the exact number.
- Line 482 – Is the volcanic plume consistently the highest aerosol layer?
- Lines 597–600 – There appear to be typographical errors in this bibliography item.
Citation: https://doi.org/10.5194/egusphere-2025-3164-RC1
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