Cascading events during the 1650 tsunamigenic eruption of Kolumbo volcano

Domain: earth_science
Published: 2023-10-26
Editorial outcome: accept

Abstract
Volcanic eruptions can trigger tsunamis, which may cause significant damage to coastal communities and infrastructure. Tsunami generation during volcanic eruptions is complex and often due to a combination of processes. The 1650 eruption of the Kolumbo submarine volcano triggered a tsunami causing major destruction on surrounding islands in the Aegean Sea. However, the source mechanisms behind the tsunami have been disputed due to difficulties in sampling and imaging submarine volcanoes. Here we show, based on three-dimensional seismic data, that ~1.2 km³ of Kolumbo’s northwestern flank moved 500–1000 m downslope along a basal detachment surface. This movement is consistent with depressurization of the magma feeding system, causing a catastrophic explosion. Numerical tsunami simulations indicate that only the combination of flank movement followed by an explosive eruption can explain historical eyewitness accounts. This cascading sequence of natural hazards suggests that assessing submarine flank movements is critical for early warning of volcanogenic tsunamis.

Introduction
Volcanogenic tsunamis have caused more than 55,000 fatalities since the late 18th century1. Tsunami generation is often due to a combination of processes, including submarine explosions, pyroclastic flows, caldera subsidence, and flank failures2. The 2022 Hunga Tonga-Hunga Ha’apai (HTHH) eruption in Tonga3,4 and the 2018 Anak Krakatau sector collapse in Indonesia demonstrated the devastating tsunami hazard of volcanic eruptions in shallow marine environments and at the land-sea boundary5. Both eruptions have become a focus of volcanological research in recent years. The 2018 tsunami of Anak Krakatau hit neighboring coasts without any warning and caused hundreds of casualties5. Satellite geodetic data from more than ten years before the event indicated deformation within the volcanic edifice6. However, it was only after the collapse that these observations were interpreted as revealing prolonged, deep-seated deformation in the buildup to the collapse7. Internal deformation of a volcanic flank preceding catastrophic failure has also been demonstrated for the 1888 Ritter Island sector collapse8,9, and episodic gravity-driven movement along deep detachment surfaces is known from several large volcanoes10–12. At Mt Etna, an average seaward motion of 3 to 5 mm per year is observed11, while the southwestern flank of Kilauea shows both a transient cm-scale yearly seaward movement and m-scale slip events accompanied by major earthquakes13.

Kolumbo is a fully submerged volcano 7 km northeast of Santorini and part of the Hellenic Volcanic Arc. It is by far the largest volcano of the Kolumbo Volcanic Chain, consisting of 24 volcanic cones formed ~350 kyrs ago14,15 (Fig. 1). Kolumbo’s edifice was created by at least five eruptive cycles, the earliest dating back more than 1 Myrs15,16. The most recent eruption, in 1650 CE, formed a cone consisting of up to ~260 m-thick stratified pumice deposits, which breached the sea surface before being destroyed by a violent explosive eruption that formed a 500-m-deep and 2500-m-wide crater17,18. The eruption deposits consist of highly vesicular rhyolitic pumice with cm-size mafic inclusions, likely reflecting an eruption triggered by mafic replenishment into a cooler silicic reservoir18,19. The 1650 eruption triggered a tsunami causing major destruction on the neighboring islands of Santorini, Ios, and Sikinos. Historical eyewitness accounts reported maximum run-up heights of 20 m on the southern coast of Ios, 240 m inundation on Sikinos20,21, and flooding of up to 2 km² of land on the eastern coast of Santorini which caused major destruction in the towns of Kamari and Perissa17,20,21 (Fig. 1b). Flooding at Kamari and Perissa was preceded by sea retreat, indicating a negative-amplitude leading wave20. Onshore tsunami deposits have been identified up to 14 m above sea level on the north coast of Santorini, 6 m above sea level in Kamari, and up to 360 m inland in Perissa as well as on Ios and Sikinos20,21.

The genesis of volcanogenic tsunamis is often complex and may involve underwater explosions, earthquakes, caldera subsidence, pyroclastic density currents, flank failures or a combination of these processes2. Even for prominent and comparably recent events, such as the 1883 eruption of Krakatau, the tsunami source mechanisms are still debated. Previous analyses of the 1650 tsunami tested the submarine emplacement of pyroclastic flows, caldera collapse and underwater explosions as potential singular source mechanisms20. However, the movement of Kolumbo’s northwestern flank (Fig. 1c) has not been considered as a source mechanism in previous simulations. In this study, we use new high-resolution 3D reflection seismic data and numerical tsunami simulations to reconstruct the mechanisms that caused the tsunami waves recorded in 1650. We investigate Kolumbo’s flank deformation and evaluate its tsunamigenic potential, as well as its role in triggering the violent explosions. Our analyses show that flank deformation initiated a cascade of events triggering the violent and tsunamigenic eruption of Kolumbo in 1650.

Results
Structural architecture of Kolumbo
High-resolution (2 m) bathymetry data reveal intricate morphological details of the cone formed by the 1650 eruption of Kolumbo (Fig. 1c). The northwestern flank of the volcano is characterized by a distinctive terraced morphology, in stark contrast to the smooth flanks to the south and east (Fig. 1c). 3D seismic reflection data reveal the subsurface architecture of this structural asymmetry (Figs. 2 and 3). While the southeastern flank comprises undeformed, sub-parallel strata, the northwestern flank displays pronounced internal deformation (Figs. 2 and 3a). This deformed sedimentary unit lies directly above the ~1600 BCE Minoan eruption ignimbrites16. Aside from the 1650 eruption, there is no evidence of other recent explosive eruptions in sediment cores22,23. Therefore, the deformation affects solely volcanic sediments deposited by the 1650 eruption. Mapping of the top and base of the deformed sediments yields a volume of ~1.2 km3, assuming a seismic velocity of 1700 m/s (±50 m/s) based on refraction seismic data15. The bathymetric data show elongated ridges that strike slope parallel around the northwestern flank of the volcanic edifice (Fig. 1c). The analysis of the 3D seismic data reveals that they are the surface expression of anticlinal folds associated with downslope compression (Figs. 2 and 3). Their curved shapes in plan form, their relative steepness, and interpreted internal thrusting indicate that the ridges are the result of compression and not contourite sediment depositional processes seen at some other submarine volcanoes24. Deformation at the toe of the flank is complex and segmented (manifesting itself in the terrace-like morphology), while a distinct detachment surface can be observed toward the top of the remnant cone (hatched region, Figs. 1c and 4a). The exposed detachment surface has a slope angle of ~19°, while the underlying strata dip at ~11°, which is significantly steeper than strata within the southwestern flank that dip at ~6° (Fig. 3a). The steeper stratigraphic dips beneath the northwestern flank are likely due to deposition onto a pre-existing remnant cone (Figs. 2 and 3a), which is not present beneath the southeastern flank. Additionally, there is a morphological step between the two slopes, as the base of the 1650 cone lies 50-100 m deeper on the northwestern side of the edifice (Fig. 3). The 1650 eruptive products were deposited on top of the remnants of a cone from a previous eruption (K3 in ref. 15), which introduces structural heterogeneities within the northwestern flank of Kolumbo, in contrast to the relatively flat southeastern flank (Fig. 3). This complex pre-eruption topography, with a steep northwestern flank, likely controlled the instability of this flank segment as slope angle is a dominant factor for slope stability25. Previous numerical simulations20 suggested a violent explosion, pyroclastic flow emplacement, and caldera subsidence as potential tsunami source mechanisms during the 1650 eruption. However, the 3D seismic data show neither indications for sizable pyroclastic flow deposits (Figs. 2 and 3) nor for ring faults that would accommodate caldera collapse (Fig. 3b). Therefore, we deem pyroclastic flow emplacement and caldera collapse as unlikely tsunami source mechanisms. The existence of a 2500-m-wide and 500-m-deep crater, however, provides clear evidence for a highly explosive eruption phase. The seismic and bathymetric datasets suggest a link between this explosion and the flank deformation. At the top of the remnant cone, the detachment surface intersects prominent ridges that are the seafloor expression of feeder dykes (Fig. 4a, d). Their present exposure is probably due to their higher mechanical stability relative to the surrounding volcanoclastic deposits, which have been eroded since the 1650 eruption. While the explosion represents an obvious tsunami source mechanism, the previously unconsidered tsunamigenic potential of the flank deformation requires careful evaluation.

Reassessment of the 1650 tsunami
Historical eyewitness accounts of tsunamis can be used to test the feasibility of tsunami simulations. For Kolumbo, the observations of higher tsunami run-up at Ios than at Santorini and sea retreat preceding inundation in eastern Santorini17,20,21 suggest a northwesterly directed wave propagation. Previous numerical simulations of the explosive eruption assumed a radial-symmetric initial wave form with a steep positive amplitude leading wave, followed by a trough that mimics the crater20. By assuming a peak wave amplitude of 250 m, these simulations could reproduce tsunami run-up heights at Santorini. However, the simulations could not reproduce the initial sea retreat at Kamari and Perissa, and they underestimated the 20 m run-up height at Ios by a factor of four. Therefore, it appears unlikely that an underwater explosion was the only source of the 1650 tsunami.

To evaluate the tsunami potential of flank deformation, we extrapolated the present-day southeastern flank slopes toward the sea surface to reconstruct a cone that just breaches the sea surface (Fig. 5) to be consistent with eyewitness accounts17,18. This pre-explosion flank topography (Fig. 5a) and the seismically-mapped detachment surface (Fig. 5b) were used as input surfaces for numerical tsunami simulations using VolcFlow26. Kolumbo’s cone consists of poorly consolidated pumice with a median dry density of 0.725 g/cm³ and median vesicularity 67.5 (ref. 18), which, depending on the inter-pore porosity, results in a bulk deposit density of 1250–1500 kg/m³. This density is significantly lower than values used in previous volcanic landslide tsunami simulations, e.g., 1900 kg/m³ at Anak Krakatau5, 2000 kg/m³ at Ritter Island27 and 2600 kg/m³ at Tenerife28. In VolcFlow simulations, the slide material density, in combination with its yield strength, controls the dynamics of flank deformation. We tested a large parameter space (Supplementary Information) with yield strengths between 2000 and 75,000 Pa and densities between 1250 and 2000 kg/m³. We compared the resulting flank deformation and tsunami heights with the geophysical observations and the eyewitness reports.

Our analyses reveal that a range of yield strength-density pairs can reproduce the observed tsunami run-up heights at Ios, Sikinos, and northern Santorini (Fig. 6a, Supplementary Figs. S1–S25). Given the deposit density range defined by the pumice sample analysis (1250–1500 kg/m³), it is possible to reproduce the tsunami observations with simulations using a yield strength between 5000 and 20,000 Pa, which is the same value range used in previous VolcFlow simulations of Anak Krakatau29 and Ritter Island27. At Perissa and Kamari, the important observation of sea retreat is reproduced, but run-up heights are underestimated (blue dashed line in Fig. 6d–h).

In addition, we simulated an explosion-induced tsunami, which requires an estimate of the peak wave amplitude, previously assumed to be in the range of 150–240 m, to be able to reconstruct tsunami observations at Santorini20. However, considering the crater rim lies in an average water depth of only 135 m, the initial wave height by the explosion is unlikely to have exceeded this. Our simulations of an explosion-induced tsunami with a peak wave height of 150 m can neither reproduce the wave height observed at southern Ios and Sikinos nor the reported initial sea retreat at Kamari and Perissa (green dotted line in Fig. 6d–h).

Since the seismic data show that both source mechanisms could have contributed to tsunamigenesis and neither the slope failure nor the explosion-induced tsunami simulations alone could reproduce eyewitness accounts, we performed additional model runs to simulate the effects of a combination of both source mechanisms, superimposing the wave field of an explosion onto that caused by flank deformation. The lag time between flank deformation and the explosion is unknown. However, we interpret that the explosion was caused by depressurization of a critical, erupting system or exposure of the feeder system, which would require lateral movement of the overlying sediment by a distance on the order of 500–1000 m. Given a simulated velocity of 3 to 4 m/s for the flank movement, this equates to a lag time of ~2 to 5 min from the initiation of the slope instability. Our results show that assuming a lag time of 4 min from the beginning of flank deformation to the explosion, and an explosion-derived initial wave height of 150 m, we are able to simulate a tsunami pattern that is consistent with all known historical eyewitness accounts (red solid line in Fig. 6). In addition, various combinations of lag time and explosion-derived initial wave height show good agreement with the run-up heights at Ios as well as the initial sea retreat and subsequent run-up heights on the eastern Santorini coastline (Supplementary Figs. S1–S25). The observed inundation of 240 m on Sikinos cannot be directly transferred to a run-up height due to the simplified topography used in the simulations and the lack of a precise location of the eyewitness account. However, the reported inundation indicates that the southeastern coast of Sikinos was affected by a tsunami with significant run-up heights. The good agreement between our simulations and the eyewitness accounts gives confidence in the combined simulation approach and highlight the complexity of tsunami generation related to the cascading chain of events during volcanic eruptions (Fig. 7). While a lateral explosion might be able to lead to a regional tsunami pattern consistent with historical eyewitness accounts, we do not have any evidence for such an explosion. We argue that the simplest explanation for tsunamigenesis, supported by our data, is flank movement followed by explosive eruptions.

Chain of events during the 1650 eruption
The combination of high-resolution marine geophysical datasets and historical eyewitness accounts offers a unique opportunity to reconstruct the sequence of volcanic processes that triggered the 1650 explosion and tsunami. The 1650 cone consists of highly vesicular pumice, which was deposited as fallout from the eruption column, where many of the large pumice clasts floated at the sea surface before becoming water-saturated and sinking18 (Fig. 7a, b). The 1650 cone had a volume of approximately 4 to 6 km³ (ref. 16), which was deposited in a very short timeframe of only 2 weeks, based on the onset of visually detectable eruption products in eyewitness accounts18,20,21. This rapid deposition has likely precluded significant consolidation of the pumice deposits covering the pre-1650 topography. The pre-1650 topography was characterized by the remnants of a cone on the northwestern side of Kolumbo from the previous eruptive cycle (K3 in Fig. 3), as well as a topographic step cutting through the volcanic edifice. Consequently, deposits from the 1650 eruption were deposited on steep slopes on the northwestern side of Kolumbo, while the southeastern side was relatively flat (Figs. 2 and 7b). ROV-dives targeting neighboring cones from the Kolumbo chain have revealed pronounced biogenic cementation of volcanic material14,30, thereby forming a stark material contrast with the overlying 1650 eruption products, which is indicated by a positive polarity reflection (Figs. 2 and 3).

Slope stability is governed by sub-seafloor effective stress (total stress minus pore pressure) and material strength properties. The 1650 pumice deposits were sensitive to slope failure triggered by dynamic loading because (1) rapid deposition precluded the development of cohesion and (2) the exceptionally low deposit density (~1250–1500 kg/m3) resulted in low effective stress within the cone. We suggest that the pronounced material contrast between the cone and the older, underlying volcanic material, as well as the steeper northwestern slope (19° compared to ~6° elsewhere), explain why the failure occurred on the northwestern flank. Eruptive activity was accompanied by earthquakes noted in the eyewitness reports18, which will have caused ground acceleration and a likely associated dynamic pore pressure increase. This scenario is consistent with the development of a listric failure surface that cuts through the northwestern flank of the cone and soles out onto the pre-1650 material, defining the detachment surface of the slope instability (Figs. 2, 3 and 6c).

The water displacement caused by the movement of the volcanic flank not only triggered a tsunami, as demonstrated by our numerical simulations, but also directly affected the dynamics of the ongoing eruption. Considering that the active vent had emerged above sea level at this stage18, failure of the northwestern flank probably caused the subaerial vent area to slide into the sea along with the flank. Based on the geometry of the detachment surface, the slope failure removed up to 200 m of material, thereby unroofing the underlying magmatic system. Assuming a bulk density of 1300–1500 kg/m³, this unroofing may have resulted in a pressure reduction of up to 2.6 to 3 MPa, affecting the underlying feeder system and magma reservoir at a depth as shallow as 2 km, as indicated by seismic full-waveform inversion results31. The failure will have exposed deeper levels in the vent directly to seawater, while crack formation and possible re-activation of existing failure planes will have allowed phreatomagmatic interactions within the edifice (Fig. 7d). Thus, both decompression through unroofing and interaction with seawater must have affected the upper parts of the magma feeding system within the timeframe of 4 min, as suggested by our model results. Decompression of the magma by unroofing will have led to an expansion of the magmatic fluid phase within the already critical system, directly followed by enhanced internal (closed-system) degassing and associated further pressure buildup.

The flank failure took place during an ongoing eruption, meaning that there was a hydraulic connection in the form of a highly vesicular magma18 between the summit region and the deeper magma feeding system. A decompression of 3 MPa in the conduit at, e.g., 10 MPa ambient pressure (or about 600 m depth within the volcano base, assuming a magma density of 1500 kg/m³) would lead to a sudden volume increase of about 50% for bubbles existing in the magma, and thus produce efficient fragmentation in the upper vent region32. The pressure released upward in the open conduit would be sufficient to increase the internal bubble pressure above the typical yield strength of about 5 MPa for a felsic magma33, leading to magma fragmentation at shallow conduit levels. The magma strain rate would suddenly exceed a critical limit34, and efficient magma fragmentation would commence at shallow levels. The increased fragmentation rates lead to a rapid downward migration of the fragmentation level, thereby initiating a chain reaction of accelerated decompression, producing sustained eruption rates, which further decompresses the deeper parts of the magma feeding system leading to a runaway process of magma ascent and subsequent depressurization. Decompression experiments35 suggest a lag time of ~180 s between initial rapid decompression and accelerated degassing caused by bubble coalescence, which would be in agreement with the assumed slope failure dynamics. Magma-seawater interactions leading to phreatomagmatic explosions36 must have played a central role at this stage, adding to the pressure buildup. The combined result of bubble expansion and phreatomagmatic explosions is rapid degassing in the magma feeding system, triggering a chain of highly explosive events and sustaining a runaway explosive eruption. Potential evidence of enhanced phreatomagmatic fragmentation of Kolumbo magma may lie in the abundance of very fine-grained tephra found in close proximity to the volcano in box cores and chemically correlated to the products of the 1650 event37.

Depressurization by unroofing is known to have triggered violent explosive eruptions such as the 1980 Mount St. Helens eruption and multiple caldera-forming eruptions at Tenerife38, and initial results suggest that this process may have triggered the 2022 HTHH eruption4. The up to 2500-m-wide crater of Kolumbo is the result of one or multiple violent explosions, which agrees well with historical eyewitness accounts18. The 1650 explosive eruption produced ~2.5 km³ (Dense Rock Equivalent (DRE) volume of ~2.5 km³) of tephra. Considering the large amounts of pumice forming the 1650 cone (~4-6 km³, ref. 16) and the reported pumice rafts floating throughout the southern Aegean Sea18, the total eruption volume was larger than 10 km³ (5 km³ DRE). In comparison, the 1980 Mount St. Helens eruption produced only 1.1 km³ of tephra, while first mass flow rate-based estimates suggest an eruption volume of ~1.9 km³ for the 2022 HTHH eruption39.

Methods
3D seismic survey
The high-resolution P-Cable 3D seismic dataset was collected during research cruise POS538 aboard R/V Poseidon in October 2019 (ref. 46). The receiver array consisted of 16 streamers (each with 8 channels, spaced 1.5625 m apart) attached to a cross cable of ~200 m length. The source was a 45 in3–45 in3 generator-injector airgun (harmonic mode), fired every 4 s, with a nominal ship speed of 3.5 knots through water. Processing included geometry definition, trace editing (removing dead and very noisy traces), static time corrections, anomalous amplitude attenuation, frequency-wavenumber (FK) filtering and trace interpolation. We then applied adaptive subtraction multiple suppression on common receiver gathers using a 1D pattern-matching algorithm. The resulting data were sorted to common midpoints on a grid with cell sizes of 3.125 m by 3.125 m, corrected for normal moveout using a water velocity of 1517 m/s, and then stacked. Gaps were filled via post-stack trace interpolation in both the inline and crossline directions. Signal to noise ratio was further improved with a post-stack 3D F‐K coherency filter. We migrated the data with a constant velocity (1517 m/s) 3D Stolt migration, followed by residual 2D finite difference migrations applied in the inline and then crossline direction. We estimated velocities for the finite difference migrations via semblance analysis of long-offset 2D seismic data that crossed our 3D survey. The final data volume has a maximum spatial resolution of 3.125 m, and a maximum vertical resolution (half wavelength) near the seafloor of ~7 m, based on a dominant frequency of ~100 Hz.

Numerical tsunami simulations
We used the numerical simulations code VolcFlow for all presented simulations (details in refs. 26–29, 47). VolcFlow simulates the slide as a fluid and couples the interaction between the slide and the water based on a depth-averaged approximation on a topography-linked coordinate system. VolcFlow applies a plastic behavior with turbulence as rheology, which is primarily controlled by yield strength and density. The code uses general depth-averaged equations of mass and momentum conservation43,48. The slide was defined by reconstructing a pre-slide topography (Fig. 5), which was achieved by using the geometry of the remaining cone and constraints about the pre-slide geometry (i.e., that the cone breached the sea surface) and mapping the detachment surface in the 3D seismic datasets as slide plane, which had to be converted into the time domain using a seismic velocity of 1.7 km/s (ref. 15). The simulations had a lateral resolution of 100 m and simulated the wave field for 30 min. We performed 20 slide simulations using various densities (1250, 1500, 1750 and 2000 kg/m³) and yield strengths (5000, 7500, 10,000, 20,000 and 50,000 Pa) to test the parameter space (see. Supplementary Figs. S1–S25). To simulate the effects of an explosion, we followed the approach by Ulvrova et al. 20 and assumed a radial-symmetric initial explosion-induced water undulation for four different peak wave heights (100, 125, 150 and 240 m). Finally, we performed 20 simulations combining a slide and explosion using the same explosion-induced water undulations and five different time gaps between slide and explosion (1, 2, 3, 4, 5 min) combined with a slide with a representative density of 1500 kg/m³ and yield strength of 7500 Pa (as described in ref. 26). For this, the initial wave field from the explosion-derived tsunami simulations was added to the wave field of the landslide tsunami simulations at one specific timestep (1, 2, 3, 4, 5 min) and the code used this superimposed wave fields for the rest of the simulations. To compare simulated wave heights with eyewitness accounts, we created maps showing the maximum wave height as well as virtual tide gauges at locations where direct tsunami observations are available. The virtual tide gauges were placed in shallow water (5–10 m and not at the coastline) to allow analyzing a potential sea retreat at each location.

Autonomous underwater vehicle (AUV) mapping
During cruise POS510 (ref. 44), detailed bathymetric data were acquired through 7 planned dives by AUV Abyss, which is equipped with the dual frequency (200/400 kHz) RESON Seabat 7125 multibeam. During the acquisition, the nominal frequency of 200 kHz was applied, and all the logged data were further processed using the open-source software package MB-System. First, the navigation was adjusted using the interactive graphical interface program MBnavadjust and then merged with the bathymetric data. The following step included identifying and cleaning erroneous beams; therefore, dedicated filters were applied and manual cleaning through 2D and 3D editors. Finally, the processed bathymetric data were gridded, yielding a spatial resolution of 2 m, using the function mbgrid and, more specifically, the Gaussian weighted mean algorithm.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "I read with great interest the paper by Jens Karstens and colleagues. The topic addressed in very\ninteresting and useful for the scientific community and not only. Understanding the processes and\nmechanisms of volcanogenic tsunamis is of great importance for protecting coastal communities and for\nbeing prepared.\nThe authors combine high-resolution three-dimensional seismic data, bathymetric data and modeling to\nreconstruct the 1650 tsunamigenic eruption of Kolumbo volcano, near Santorini. They also use\neyewitness data to assess their results.\nIn my view, the paper is very well organized, the methodological approach is clear, and the conclusions\nare supported by the data.", "reviewer_2": "This is a very interesting study about the Kolombo volcano that collapsed 470 years ago, triggering a\ntsunami in the Aegean Sea. The authors explore high resolution seismic data to study the internal\nstructure, and develop a conceptual model of depressurized magma associated with the unloading\nevent. The provided data includes bathymetric data, 3D seismic reflection profiles, and tsunami\nsimulations, all of which of high quality and nicely demonstrated.\nI enjoyed reading this work, but also have a number of suggestions that may improve the work.\nImportantly i ask the authors to more carefully choose the wording (often imprecise), to better use the\ndata and develop a quantitative analysis (currently field data is mainly quantitative and descriptive),\nand to make the data publicly available. Once these and the moderate points listed below are considered,\ni believe the manuscript will make an excellent contribution and be well placed in ncomms.\nPoint listing:\n1) The abstract is generally very vague and inprecise: i suggest complete rewriting, toning down\nprovocative statements, and adding more detail on what actually was done, and add quantitative results\nif available.\n2) L 23: how was the depressurization determined/quantified?\n3) L 24: what means \"notoriously unstable\"? how determined? it is a very vague statement. I would\nexpect rock mechanical tests to support this when reading this abstract.\n4) L 27: ...mechanism followed by submarine explosive eruption. >> maybe it was simultaneously? Can\nthe chicken and egg really be separated here?\n5) L 28: You write\" Our analysis represents the first integrated quantitative reconstruction of a cascading\nsequence of natural hazards\". This obviously is wrong. I do not start listing citations of other cascading\nstudies, but there are many integrated and quantitative reconstructions and monitored cascades, from\nearthquakes/landslides/liquefaction or from earthquake/volcano/landslide or other cascades. Please\nconsider toning down your statements or expect a flood of critical comments after you are publishing\nthis.\n6) L 34: \"While there is little known...\" > this statement is about the eruption or the tsunami of HTHH?\nThere are papers out on the HTHH now. Please implement and rewrite.\n7) L 36: Replace \"satellite altimetry\" by \"satellite geodetic\"\n8) L 39: \"Internal deformation...\" > can you add more details on how fast these displacements actually\nare at the cases provided? Are we talking about mm or m displacements? During which period?\n9) L41-42: I would add here a sentence or two making clear where new research is demanded, or what is\nactually the added value of this paper. In actually most examples of volcano-induced tsunami, the search\nfor the trigger mechanism remained debated. Even for the 1883 and again the 2018 Krakatau collapses,\ndiscussion persists weather the tsunami were triggered by the flank collapse, by a caldera, by\nexplosions, by pyroclastic flows entering the sea, or by more than one of these hazards. Please better\nintroduce this state of the art.\n10) L 41: Here you refer to Mt Etna and Kilauea > for all these cases mentioned, cascading sequences\nhave been proposed. If this is an important element of the paper (as proposed in your abstract), but this\nis not \"the first integrated work\".\n11) L 44: should read \"...350 ka ago\"\n12) Authors use inconsistent formats. \"Year\" is abbreviated on L 45 as \"yrs\", and just one line above on L\n44 as \"a\".\n13) L 45: 1650 of what? a.d.?\n14) L 52: \"Sikinos\" > please add citations after this statement before the next statement follows.\n15) L 56: 360 m > this is a horizontal measure?\n16) L 58: previous studies also speculate about an interlinked mechanism\n17) Structural architecture of Kolumbo > this chapter (the result chapter) is highly qualitative only and\ncontains a mixture of descriptive terms, interpretation and discussion. I suggest to carefully check again\nhow a quantitative analysis can be strengthened, where dimensions of blocks, thicknesses of layers,\noffsets of faults and deviations in strike are determined and investigated.\n18) L 66. i am aware that the journals format has methods at the end of the work. But it is a bit difficult\nto follow if it is not mentioned before that here a new marine dataset is analysed showing the\nbathymetry and lithology variations associated with a submarine flank failure.\n19) L 70-71: maybe it would be good to better explain how you can see this in figure 2. I presume that by\nfollowing the traces of lithology you determine if a flank is deformed or undeformed? Currently the text\nreads like a rough interpretation, but lacks the scientific description.\n20) L 75: \"of ~1.2 km^3\" > please add errors. Similar also for other estimates, such as the seismic\nvelocity of 1700 m/s (same line) i would expect to see a more rigorous analysis. What are the\nmethod/data and analysis uncertainties? These are propagating into the volume errors, i presume.\n21) L 77: \"Detailed analysis of 3D seismic data...\" > what is meant by that? You just zoom in an look\ncloser, or you use any particular technique to improve the analysis? Please add some details here.\n22) L 78: i am wondering how much subject interpretation is allowed in a \"results\" paragraph. Maybe\nthe authors may want to reconsider the structure here, i usually prefer separation of data analysis and\ninterpretation.\n23) L 79: dont use \"the fact\". If i read this, i start being suspicious. Better is to provide solid data and\narguments, and therewith to substantiate your statement.\n24) L 80: \"unequivocally\" > seems we are here leaving scientific literature. Is that subjective feeling? The\ntext is not getting more convincing with that type of expression.\n25) L 81: \"... not contourite sedimentation\" > what is meant here? That it is not a continental rise?\nConsider rewording.\n26) L 81: Bathymetry or Morphology is complex, which suggest deformation is partitioned by distinct\nblocks... or similar. Please consider rewording. The word \"deformation\" is used by geodesists in a\ndifferent way.\n27) L 82: why is it a decollement? this seems rather a headwall, with an unknown amount of erosion.\n28) L 84: this slope of 19° is rather shallow, especially as tension faults at the surface and at other deep\nlistric landslide expose much steeper elsewhere. Does this suggest the landslide to be translational\nrather than rotational? Then it should be not deep rooted. Please consider to add such an analysis /\ndiscussion.\n29) L 90: Please explain why the morphological step (or kink in slope) \"likely\" controls the instability.\n30) L 93-95: Can you really rule this out? Since HTHH we have learned that large explosions occur and\ntrigger tsunamis without deposition of \"sizeable pyroclastic flows\", and that smaller local tsunami are\ntriggered by very localized PDCs. Please phrase it more carefully.\n31) L 98: is it the decollement or the amphitheater?\n32) L 101: \"obvious\" > Please tone down, and choose a more careful wording.\n33) L 113: Maybe these model constraints are unlikely. Explosions may also be directed or lateral, which\nwas not tested by these previous modelling studies.\n34) L 126: Are the \"eyewitness reports\" available? Add reference of those used in here.\n35) L 134-140: i do not understand why an explosion-induced tsunami model is shown in the main text,\nalthough before it is stated that this is ruled out. Consider moving this to the supplement.\n36) L 141: \"Seismic data clearly show...\" > delete \"clearly\". Readers want to be convinced by data and\narguments, and not by subjective wordings.\n37) L 146: \"we attribute the explosion to depressurization of...\" > i do not understand this. Consider\nrewording.\n38) L 147: what is a lateral translation? A displacement? A dislocation? An impulse?\n39) L 148: \"deformation velocity of 3 to 4 m/s\" > please check your terminology, also here it is wrong.\nDeformation refers to the change in size or shape of an object. Displacements are the absolute change\nin position of a point on the object. You refer to displacement velocity here. Here and at many other\nplaces in the manuscript; please check very carefully.\n40) L 151: \"we are able to reproduce all observations\" > also here it is needed to more carefully phrase\nthis. How complete are these observations, how was this preselected? Please tone down the language.\n41) L 174: The effective stress is related to total stress and pore pressure. Is it this what the authors\nrefer to?\n42) L 177 and following: the discussion about material contrasts can be strengthened, especially as a\nnumber of new studies suggest that these contrasts can also evolve by hydrothermal alteration.\n43) L 181: why the ground acceleration has to be \"strong\"?\n44) L 181: why \"ultimately\"?\n45) L 184: maybe i missed something here, but what exactly is meant by \"water displacement\"?\n46) L 187-88: why it has to be instantaneous, and what is near-instantaneous. These phrases are all very\ndescriptive, not scientific, and leave behind a rather mixed sceptical reader. Please carefully rewrite\nthese sentences.\n47) L 192: these 2.6 - 3 MPa assume lithostatic unloading, right?\n48) L 197: an ambient pressure of 10 MPa would correspond to which depth and magmatic pressure?\n49) L 198 and following. I recommend discussing this more openly. Not only bubble growth may follow.\nThere may be also reactivations of failure planes, the Coulomb failure stress may change, and other\neffects may have played a role.\n50) L 204: why eruption rates should increase? Please be careful to not end up in a purely speculative\ndiscussion, which seems undermining an otherwise really nice study and database.\n51) L 206...: rapid, catastrophc, highly explosive, ... please tone down.\n52) L 208: i do not understand why authors now speculate about bubble coalescence. Any support from\nthe field?\n53) L 246: which several active volcanoes are these?\n54) L 254: eruptions bore similarities... > is this english? I am not a native speaker, but this sounds\nincorrect.\n55) L 261: how large is the significance mathematically?\n56) L 272-274: This is not fully correct. Years prior to the Anak Krakatau collapse, a scientific paper\nforecasted the direction, scale and threat of a sector collapse. The problem is more complex, where\nespecially communication strategies and awareness is lacking. Please consider looking into the related\nliterature before speculating.\n57) L 372: 372 Materials & Correspondence. For data enquiries, please contact Jens Karstens. I think this\nis NOT appropriate nowadays anymore. Please upload bathymetric data and ROV images to\nsupplementary or an accessible online database.\nFigure 1: A) Figs should read Fig. B) hard to read and small text. C) add scales of elevation (or is it the\nsame as in B)?), and make distance scale more visible. The label \"Deformed flank\" appears at a location\nof erosive gullies.\nFigure 2: Very nice. Listric faults usually come with block wise and antithetic faults. Is the small graben\nstructure showing this; or why authors highlight outward-dipping faults only?\nFigure 3. Can the dimension of the dikes be estimated? How shure are authors this plane is the actual\n\"sliding plane\"? Can B, C and D images be located on the A map?\nFigure 5: the block diagrams lack important structural features from this work, such as the decollement,\nsurface faults and so on. I suggest to try having it less speculative, and more closely related to the actual\nfindings of this manuscript.", "reviewer_3": "The paper provides a very interesting investigation of the 1650 Kolumbo tsunamigenic eruption. Starting\nfrom the analysis of high-resolution three-dimensional seismic data, the authors provide a novel\nhypothesis regarding the complex sequence of events that culminated in the 1650 explosion. The\nhypothesis is validated by simulating the ensuing tsunami starting from three different generation\nmechanisms and by comparing the results with the available historical accounts on the tsunami features\n(polarity of the first arrival and maximum wave amplitudes at five different sites/areas). The conclusion\nthat the tsunami was likely generated by the combined effect of a submarine landslide along the\nnorthwestern flank of the volcano followed after few minutes by the explosion seems sound and well\nsupported by data interpretation and tsunami simulations.\nSo, my opinion is that the paper deserves to be published.\nI have nonetheless a few issues to raise, which I think could contribute to make the paper more\ncomplete.\nAs a tsunami modeller, I am especially interested in some modelling details. I must admit I am not\nfamiliar with VolcFlow, but I guess it shares some common features with other numerical codes.\n- If applicable, what was the spatial resolution used for the numerical simulations?\n- For the landslide simulation, what kind of rheology was adopted? In understand you specified density\nand yield strength, but this could apply to different rheologies.\n- In the depth averaged equations, are non-linear and/or dispersion terms accounted for in this study?\n- A delicate point regards the combined generation mechanism. The authors state: \"[...] to simulate the\neffects of a combination of both source mechanisms, superimposing the wavefield of an explosion onto\nthat caused by flank deformation.\". Does this mean the two mechanisms were treated separately and\nthen the results summed together to obtain the combined effect? If this is true, then I think this\nprocedure is not appropriate for highly non-linear generation mechanisms like the ones considered. I\nask the authors to comment on this.\n- How are the coastal boundaries treated? From the inspection of the computed tide gauge-records, it\nlooks like a minimum depth has been used, pointing at the idea that linear simulations were run. Please\nclarify, taking also into account that, especially for the explosion, the tsunami generation mechanism is\nexpected to be highly non-linear (see also my previous point).\nMoreover, I ask the authors to detail more the criterion adopted to establish the water elevation\nthreshold to assess the consistency with the historical accounts. In particular, in Sikinos the historical\ninformation regards an inundation extent of 240 m: how is this converted into maximum water\nelevation? If linear tsunami simulations are run and here non inundation is modelled, where are the\nmaximum elevation computed? Along the coastline with a minimum depth attached? In correspondence\nwith a selected isobath? Using observed run-up in the comparison with computed maximum water\nelevations could not be appropriate and my bias the consistency assessment. Can the authors be more\ndetailed on this aspect?\nFew typos and possible improvements are listed hereafter.\nRow 52: \"western coast of Santorini\": is it \"eastern coast of Santorini\"?\nRow 95: here the width of the crater is indicated in 2500 m (as in two 217), while at row 47 it is of 1500\nm. I am a bit confused.\nRow 131: \"Krakatau\" instead of \"Kraktau\".\nRow 232: separate \"whichwas\".\nRow 282: \"Christiana\" instead of \"Christian\"?\nFigure 2: Correct \"Remant\" into \"Remnant\" in all three panels.\nRow 3512: (1,2,3,4,5 min).\nSupplement 2, Figures S5 - S26.\nIn the caption, it would be desirable to summarise very briefly the criteria used to assess the consistency\nwith the historical accounts. Maybe you could add in each tide gauge record plot an horizontal line\nshowing the imposed threshold in amplitude.\nBest regards,\nAlberto Armigliato"}, "author_response": "We would like to thank Alberto Armigliato and two anonymous reviewers for their helpful and con-\nstructive comments, which helped us to improve the quality and accessibility of the manuscript. Follow-\ning the recommendations and advice of the reviewers:\n1) We have updated the abstract following reviewer 2’s advices, while shortening it significantly\nto fulfil the journal requirements\n2) We have moved the figure showing the topographies used as input for the numerical simulations\nfrom the supplement to the main text.\n3) We have added an additional figure showing a 3D view on the seismic dataset.\n4) We have edited all figures according to journal requirements\n5) We have added a detailed data availability statement (uploading/data management process is\nstill in progress)\nIn the following, you can find a detailed point-to-point response (line numbers refer to the revised man-\nuscript without track changes):\nREVIEWER COMMENTS\nReviewer #1:\nI read with great interest the paper by Jens Karstens and colleagues. The topic addressed in very inter-\nesting and useful for the scientific community and not only. Understanding the processes and mecha-\nnisms of volcanogenic tsunamis is of great importance for protecting coastal communities and for being\nprepared.\nThe authors combine high-resolution three-dimensional seismic data, bathymetric data and modeling\nto reconstruct the 1650 tsunamigenic eruption of Kolumbo volcano, near Santorini. They also use eye-\nwitness data to assess their results.\nIn my view, the paper is very well organized, the methodological approach is clear, and the conclusions\nare supported by the data.\nWe appreciate this positive feedback.\nReviewer #2:\nThis is a very interesting study about the Kolombo volcano that collapsed 470 years ago, triggering a\ntsunami in the Aegean Sea. The authors explore high resolution seismic data to study the internal struc-\nture, and develop a conceptual model of depressurized magma associated with the unloading event. The\nprovided data includes bathymetric data, 3D seismic reflection profiles, and tsunami simulations, all of\nwhich of high quality and nicely demonstrated.\nI enjoyed reading this work, but also have a number of suggestions that may improve the work. Im-\nportantly i ask the authors to more carefully choose the wording (often imprecise), to better use the data\nand develop a quantitative analysis (currently field data is mainly quantitative and descriptive), and\nto make the data publicly available. Once these and the moderate points listed below are considered, i\nbelieve the manuscript will make an excellent contribution and be well placed in ncomms.\nWe appreciate the reviewer’s positive feedback and the detailed and constructive comments and sug-\ngestions.\nComment 1: The abstract is generally very vague and imprecise: I suggest complete rewriting, toning\ndown provocative statements, and adding more detail on what actually was done, and add quantitative\nresults if available.\nWe acknowledge the reviewer’s impression of the abstract. We have rewritten parts of the abstract, also\nto fulfil the journal’s requirements for abstract length. We are satisfied that the revised abstract is a solid\nreflection of the research carried out and the most important findings:\nVolcanic eruptions can trigger tsunamis, which may cause significant damage to coastal commu-\nnities and infrastructure. Tsunami generation during volcanic eruptions is complex and often due\nto a combination of processes. The 1650 eruption of Kolumbo submarine volcano triggered a tsu-\nnami causing major destruction on surrounding islands in the Aegean Sea. However, the source\nmechanisms behind the tsunami have been disputed due to difficulties in sampling and imaging\nsubmarine volcanoes. Three-dimensional seismic data show that ~1.2 km³ of Kolumbo’s north-\nwestern flank moved 500 – 1000 m downslope along a basal detachment surface. This movement\nis consistent with depressurization of the magma feeding system, causing a catastrophic explosion.\nNumerical tsunami simulations indicate that only the combination of flank movement followed by\nan explosive eruption can explain historic eyewitness accounts. This cascading sequence of natural\nhazards suggests that assessing submarine flank movements is critical for early warning of vol-\ncanogenic tsunamis.\nComment 2: L 23: how was the depressurization determined/quantified?\nWe determined this based on our reconstruction of the cone’s pre-slide topography (see new figure 5),\nwhich is described in lines 202 to 206: “Based on the geometry of the detachment surface, the slope\nfailure removed up to 200 m of material from the underlying system. Assuming a bulk density of\n1,300 to 1,500 kg/m³, this may have resulted in a pressure reduction of up to 2.6 to 3 MPa, affecting\nthe underlying feeder system and magma reservoir at a depth as shallow as 2 km, as indicated by\nseismic full-waveform inversion32.”\nComment 3: L 24: what means \"notoriously unstable\"? how determined? it is a very vague statement. I\nwould expect rock mechanical tests to support this when reading this abstract.\nWe agree that this statement is too vague. We have removed the words, which were indeed superfluous.\nComment 4: L 27: ...mechanism followed by submarine explosive eruption. >> maybe it was simulta-\nneously? Can the chicken and egg really be separated here?\nYes, we think we can separate this with the tsunami simulations. The observations of an initial sea retreat\nat eastern Santorini points towards this. If both had been triggered simultaneously, the tsunami signal of\nboth processes (slide and explosion) would have superimposed resulting in a wave peak arriving first.\nSuch a scenario is not supported by the sea retreat at eastern Santorini.\nComment 5: L 28: You write\" Our analysis represents the first integrated quantitative reconstruction of\na cascading sequence of natural hazards\". This obviously is wrong. I do not start listing citations of\nother cascading studies, but there are many integrated and quantitative reconstructions and monitored\ncascades, from earthquakes/landslides/liquefaction or from earthquake/volcano/landslide or other cas-\ncades. Please consider toning down your statements or expect a flood of critical comments after you are\npublishing this.\nWe agree with this and we have rephrased this part of the abstract.\nComment 6: L 34: \"While there is little known...\" > this statement is about the eruption or the tsunami\nof HTHH? There are papers out on the HTHH now. Please implement and rewrite.\nWe agree and have rephrased the sentence in line 34:” Both eruptions have become a focus site for\nvolcanological research in recent years.”\nComment 7: L 36: Replace \"satellite altimetry\" by \"satellite geodetic\"\nWe changed the text accordingly.\nComment 8: L 39: \"Internal deformation...\" > can you add more details on how fast these displacements\nactually are at the cases provided? Are we talking about mm or m displacements? During which period?\nWe added in lines 41 to 43:” At Mt Etna, an average seaward motion of 3 to 5 mm per year is\noberved11, while the southwestern flank of Kilauea shows both a transient cm-scale yearly seaward\nmovement, as well as m-scale slip events accompanied by major earthquakes13.”\nComment 9: L41-42: I would add here a sentence or two making clear where new research is demanded,\nor what is actually the added value of this paper. In actually most examples of volcano-induced tsunami,\nthe search for the trigger mechanism remained debated. Even for the 1883 and again the 2018 Krakatau\ncollapses, discussion persists weather the tsunami were triggered by the flank collapse, by a caldera,\nby explosions, by pyroclastic flows entering the sea, or by more than one of these hazards. Please better\nintroduce this state of the art.\nWe have added the following sentences in lines 59 to 62: “The genesis of volcanogenic tsunamis is\noften complex and may involve underwater explosions, earthquakes, caldera subsidence, pyro-\nclastic density currents, flank failures or a combination of these processes22. Even for prominent\nand comparably recent events, such as the 1883 eruption of Krakatau, the tsunami source mech-\nanisms are still debated.”.\nComment 10: L 41: Here you refer to Mt Etna and Kilauea > for all these cases mentioned, cascading\nsequences have been proposed. If this is an important element of the paper (as proposed in your ab-\nstract), but this is not \"the first integrated work\".\nWe have removed this statement in the revised abstract.\nComment 11: L 44: should read \"...350 ka ago\"\nWe changed the text accordingly.\nComment 12: Authors use inconsistent formats. \"Year\" is abbreviated on L 45 as \"yrs\", and just one line\nabove on L 44 as \"a\".\nWe use “yrs” now throughout.\nComment 13: L 45: 1650 of what? a.d.?\nWe added “CE”.\nComment 14: L 52: \"Sikinos\" > please add citations after this statement before the next statement fol-\nlows.\nWe have added the reference to Ulvrova et al., 2016.\nComment 15: L 56: 360 m > this is a horizontal measure?\nYes, the “inland” indicates this.\nComment 16: L 58: previous studies also speculate about an interlinked mechanism\nThis is correct. The analyses themselves are not interlinked, which is the argument that we intended to\nmake here. We have changed “proposed” to “tested” to be more precise now.\nComment 17: Structural architecture of Kolumbo > this chapter (the result chapter) is highly qualitative\nonly and contains a mixture of descriptive terms, interpretation and discussion. I suggest to carefully\ncheck again how a quantitative analysis can be strengthened, where dimensions of blocks, thicknesses\nof layers, offsets of faults and deviations in strike are determined and investigated.\nWhile we acknowledge the request to be more quantitative, we are not able to be quantitative in the way\nthat is being requested and the scope of the study does not require this. We have been quantitative about\nthe volume of deformed sediments, based on careful mapping of the top and base of the deformed ma-\nterial. We do not observe displaced blocks that can be measured, nor can we determine discrete offset\nalong faults in the deformed region. Even if we could measure these things, they would not give us better\nconstraints on the acceleration and velocity of flank deformation – the parameters that would be required\nfor more thorough constraints of tsunami generation. Despite this, we think that the strength of our study\nlies in the fact that we can link flank deformation to tsunami generation, and thereby test historical\nobservations of the tsunami impact at different locations.\nComment 18: L 66. i am aware that the journals format has methods at the end of the work. But it is a\nbit difficult to follow if it is not mentioned before that here a new marine dataset is analysed showing\nthe bathymetry and lithology variations associated with a submarine flank failure.\nSince this is the requirement of the journal, we can’t address this comment.\nComment 19: L 70-71: maybe it would be good to better explain how you can see this in figure 2. I\npresume that by following the traces of lithology you determine if a flank is deformed or undeformed?\nCurrently the text reads like a rough interpretation, but lacks the scientific description.\nWe determine deformation of the flank due to the pronounced folding of internal reflections. Such ob-\nservations are typical indicators for sediment deformation during mass movements. See lines 75-76:\n“While the southeastern flank comprises undeformed, sub-parallel strata, the northwestern flank dis-\nplays pronounced internal deformation (Figs. 2 and 3a).” We have added a more detailed description to\nthe figure caption of figure 2: “Semi-transparent orange regions represent material deposited by\nthe 1650 eruption. Folded and disrupted seismic reflections within the northwestern flank of the\nvolcano are the result of internal deformation, while parallel reflections within the southeastern\nflank of the volcano indicate the absence of deformation. Tentative interpretation of a thrust be-\nneath compressional folding is shown by the broken black line in (a), soling into the basal detach-\nment surface (broken pink line).”\nComment 20: L 75: \"of ~1.2 km^3\" > please add errors. Similar also for other estimates, such as the\nseismic velocity of 1700 m/s (same line) i would expect to see a more rigorous analysis. What are the\nmethod/data and analysis uncertainties? These are propagating into the volume errors, i presume.\nThe seismic velocities were determined in a previous study (Supplement of Preine et al., 2022). We\ndraw reference to this on Line 81. This analysis resulted in a velocity of 1,680 m/s for the shallowest\nunit of Kolumbo (K5) and 1,720 m/s for the cone from previous activity (K3). We now write “1700 m/s\n(±50 m/s)”. However, this has only minor impact on the volume calculation and thus the ~1.2 km³ is\nstill valid.\nComment 21: L 77: \"Detailed analysis of 3D seismic data...\" > what is meant by that? You just zoom in\nan look closer, or you use any particular technique to improve the analysis? Please add some details\nhere.\nWe removed “detailed”. The 3D analysis involves scrolling through very narrowly spaced seismic pro-\nfiles, which enables us to make interpretation with higher confidence compared to having only a single\n2D seismic profile available.\nComment 22: L 78: i am wondering how much subject interpretation is allowed in a \"results\" paragraph.\nMaybe the authors may want to reconsider the structure here, i usually prefer separation of data anal-\nysis and interpretation.\nWhile we appreciate this point, and acknowledge that other journals ask for a stricter delineation of\nobservations and interpretations, the general style of Nature Communications allows interpretative state-\nments in the results section. This style can allow the paper to flow better.\nComment 23: L 79: dont use \"the fact\". If i read this, i start being suspicious. Better is to provide solid\ndata and arguments, and therewith to substantiate your statement.\nWe agree and changed “fact” to “observation”.\nComment 24: L 80: \"unequivocally\" > seems we are here leaving scientific literature. Is that subjective\nfeeling? The text is not getting more convincing with that type of expression.\nWe removed this statement.\nComment 25: L 81: \"... not contourite sedimentation\" > what is meant here? That it is not a continental\nrise? Consider rewording.\nWe changed the sentence to “Their curved shapes in planform, their relative steepness, and inter-\npreted internal thrusting, indicate that the ridges are the result of compression and not contourite\nsediment depositional processes seen at some other submarine volcanoes25.”\nComment 26: L 81: Bathymetry or Morphology is complex, which suggest deformation is partitioned by\ndistinct blocks... or similar. Please consider rewording. The word \"deformation\" is used by geodesists in a\ndifferent way.\nWhile we acknowledge that the word “deformation\" can be used by different groups in different contexts\nto mean different things, the word is very commonly used to describe changes in the geometry of reflec-\ntions caused by movement (either extensional or compressional movements). It is a common descriptive\nterm used in the study of submarine landslides / flank collapse processes.\nComment 27: L 82: why is it a decollement? this seems rather a headwall, with an unknown amount of\nerosion.\nWe are referring to the basal detachment surface that our data image in the upper parts of the deformed\nflank. We highlight this in Figure 1c and 3a. We are not talking about a headwall, which we agree can\nnot be defined as a decollement. However, we agree that the word decollement is perhaps not the best\nterm, since it is commonly used for a subduction interface. Therefore, we have opted to change the term\nto “detachment surface” and have updated the text and figures accordingly. We point clearly to this\nfeature in the figures.\nComment 28: L 84: this slope of 19° is rather shallow, especially as tension faults at the surface and at\nother deep listric landslide expose much steeper elsewhere. Does this suggest the landslide to be trans-\nlational rather than rotational? Then it should be not deep rooted. Please consider to add such an\nanalysis / discussion.\nSince we observe a relatively flat detachment surface, we do indeed think that the flank deformation is\nmore toward the translational style of movement than rotational movement. We have added the annota-\ntion “translational movement along detachment surface” to the block diagram in Fig. 7c, to clarify\nhow we think the failure took place.\nComment 29: L 90: Please explain why the morphological step (or kink in slope) \"likely\" controls the\ninstability.\nThe morphological step was likely not the most important factor for the instability, but the steep flanks\nof the pre-1650 topography. We have changed the statement: “The 1650 eruptive products were de-\nposited on top of remnants of a cone from a previous eruption (K3 in ref. 15), which introduce\nstructural heterogeneities within the northwestern flank of Kolumbo, in contrast to the relatively\nflat southeastern flank (Fig. 2). This complex pre-eruption topography, with a steep northwestern\nflank, likely controlled the instability of this flank segment as slope angle is a dominant factor for\nslope stability26.”\nComment 30: L 93-95: Can you really rule this out? Since HTHH we have learned that large explosions occur and\ntrigger tsunamis without deposition of \"sizeable pyroclastic flows\", and that smaller local tsunami are\ntriggered by very localized PDCs. Please phrase it more carefully.\nWe have toned this down and rephrased to: “Therefore, we deem pyroclastic flow emplacement and\ncaldera collapse as unlikely tsunami source mechanisms.”\nComment 31: L 98: is it the decollement or the amphitheater?\nWe have changed the term to “detachment surface”, which is a suitable descriptive term for this ob-\nservation.\nComment 32: L 101: \"obvious\" > Please tone down, and choose a more careful wording.\n“Obvious” is an appropriate term here. One definition of the word is “easily perceived”. We would\ndefinitely argue that a volcanic explosion is an easily perceived tsunami source mechanism.\nComment 33: L 113: Maybe these model constraints are unlikely. Explosions may also be directed or\nlateral, which was not tested by these previous modelling studies.\nWe understand the point here. We do not have any indications for a significantly lateral explo-\nsion, while we do have strong evidence for flank deformation. That is why we are testing the\ntsunamigenic potential of the flank deformation in this study. We have added a sentence toward\nthe end of the manuscript stating: “While a lateral explosion might be able to lead to a regional\ntsunami pattern consistent with historical eyewitness accounts, we do not have any evidence for\nsuch an explosion. We argue that the simplest explanation for tsunami genesis, supported by our\nnew data, is flank movement followed by explosive eruptions.” In lines 167 - 170.\nComment 34: L 126: Are the \"eyewitness reports\" available? Add reference of those used in here.\nThe eyewitness reports have been documented in the studies (in lines 51 - 58) that we cite in the section\n“Reassessment of the 1650 tsunami”. Citations are provided in this section to the relevant literature\nwhere these observations are stated.\nComment 35: L 134-140: i do not understand why an explosion-induced tsunami model is shown in the\nmain text, although before it is stated that this is ruled out. Consider moving this to the supplement.\nPerhaps there is a slight misunderstanding here. We do not rule out the explosion source. Rather, we do\nnot think that an explosion by itself can be the primary mechanism to explain all of the historical obser-\nvations. Our seismic reflection observations and modelling results show that flank movement is most\nlikely to have been the primary control on tsunami genesis. We think that explosive eruptions con-\ntributed to the tsunami, as stated in the lines 156 – 161: “Our results show that assuming a lag\ntime of 4 minutes from the beginning of flank deformation to the explosion, and an explosion-\nderived initial wave height of 150 m, we are able to simulate a tsunami pattern that is consistent\nwith all known historical eyewitness accounts (red solid line in Fig. 6). In addition, various com-\nbinations of lag time and explosion-derived initial wave height show good agreement with the run-\nup heights at Ios as well as the initial sea retreat and subsequent run-up heights on the eastern\nSantorini coastline (Supplement).”.\nComment 36: L 141: \"Seismic data clearly show...\" > delete \"clearly\". Readers want to be convinced\nby data and arguments, and not by subjective wordings.\nAgreed. We have removed the word “clearly”. In addition we changed “high confidence” to “confi-\ndence”.\nComment 37: L 146: \"we attribute the explosion to depressurization of...\" > i do not understand this.\nConsider rewording.\nWe have changed the wording to “However, we interpret that the explosion was caused by depres-\nsurisation…”\nComment 38: L 147: what is a lateral translation? A displacement? A dislocation? An impulse?\nAgree that this part of the sentence was ambiguous. We have changed the wording to: “… which would\nrequire lateral movement of the overlying sediment by a distance on the order of 500 - 1000 m.”\nComment 39: L 148: \"deformation velocity of 3 to 4 m/s\" > please check your terminology, also here it\nis wrong. Deformation refers to the change in size or shape of an object. Displacements are the absolute\nchange in position of a point on the object. You refer to displacement velocity here. Here and at many\nother places in the manuscript; please check very carefully.\nAgreed. We have changed the wording to “Given a simulated velocity of 3 to 4 m/s for the flank\nmovement, …”\nComment 40: L 151: \"we are able to reproduce all observations\" > also here it is needed to more\ncarefully phrase this. How complete are these observations, how was this preselected? Please tone down\nthe language.\nTo acknowledge that there is much that we don’t know about the tsunami, and that we can only base our\nunderstanding on the eyewitness reports that have been written down, we have changed the wording\nhere slightly to: “Our results show that assuming a lag time of 4 minutes from the beginning of\nflank deformation to the explosion, and an explosion-derived initial wave height of 150 m, we are\nable to simulate a tsunami pattern that is consistent with all known historical eyewitness ac-\ncounts.”\nComment 41: L 174: The effective stress is related to total stress and pore pressure. Is it this what the\nauthors refer to?\nYes, that is what we are referring to. We have changed the wording slightly to: “Slope stability is\ngoverned by sub-seafloor effective stress (total stress minus pore pressure) and material strength\nproperties.“\nComment 42: L 177 and following: the discussion about material contrasts can be strengthened, espe-\ncially as a number of new studies suggest that these contrasts can also evolve by hydrothermal altera-\ntion.\nConsidering that the 1650 Cone has been formed in a relatively short time interval, it appears unlikely\n(although not impossible) that hydrothermal alteration may have contributed to the slope failure. We\nwould be happy to integrate this into the discussion references if the reviewer would point to specific\npublications.\nComment 43: L 181: why the ground acceleration has to be \"strong\"?\n“Strong” is a qualifier that we cannot quantify. As such, we agree that the word is not useful. We have\nremoved it and now just state “ground acceleration”.\nComment 44: L 181: why \"ultimately\"?\nWe have removed the word “Ultimately”.\nComment 45: L 184: maybe i missed something here, but what exactly is meant by \"water displace-\nment\"?\nAgree that the start of this sentence is not very clear. We have reworded it to: “The water displacement\ncaused by movement of the volcanic flank not only triggered a tsunami, …”\nComment 46: L 187-88: why it has to be instantaneous, and what is near-instantaneous. These phrases\nare all very descriptive, not scientific, and leave behind a rather mixed sceptical reader. Please carefully\nrewrite these sentences.\nThis is a fair point. We have rewritten these sentences and removed the word “instantaneous”.\nComment 47: L 192: these 2.6 - 3 MPa assume lithostatic unloading, right?\nCorrect – this assumes unloading of the highly porous and water saturated pumice material. The density\nwe use for the pressure calculation here is the water-saturated density of the sediment.\nComment 48: L 197: an ambient pressure of 10 MPa would correspond to which depth and magmatic\npressure?\nFair comment – We have included such information in the revised text: “…10 MPa ambient pressure\n(or about 600 m depth within the volcano base, assuming a magma density of 1,500 kg/m³)…”\nComment 49: L 198 and following. I recommend discussing this more openly. Not only bubble growth\nmay follow. There may be also reactivations of failure planes, the Coulomb failure stress may change,\nand other effects may have played a role.\nWe have followed this suggestion and discussed the scenario in more detail, and now mention failure\nplane reactivation as an additional plausible cause for increased phreatomagmatic activity. We think that\ndetailed descriptions of Coulomb failure are beyond the scope of the paper: “The water displacement\ncaused by movement of the volcanic flank not only triggered a tsunami, as demonstrated by our\nnumerical simulations, but also directly affected the dynamics of the ongoing eruption. Consider-\ning that the active vent had emerged above sea level at this stage18, failure of the northwestern\nflank probably caused the subaerial vent area to slide into the sea along with the flank. Based on\nthe geometry of the detachment surface, the slope failure removed up to 200 m of material, thereby\nunroofing the underlying magmatic system. Assuming a bulk density of 1,300 to 1,500 kg/m³, this\nunroofing may have resulted in a pressure reduction of up to 2.6 to 3 MPa, affecting the underlying\nfeeder system and magma reservoir at a depth as shallow as 2 km, as indicated by seismic full-\nwaveform inversion results32. The failure will have exposed deeper levels in the vent directly to\nsea-water, while crack formation and possible re-activation of existing failure planes will have\nallowed phreatomagmatic interactions within the edifice (Fig. 7d). Thus, both decompression\nthrough unroofing and interaction with seawater must have affected the upper parts of the magma\nfeeding system within the timeframe of four minutes, as suggested by our model results. Decom-\npression of the magma by unroofing will have led to expansion of the magmatic fluid phase within\nthe already critical system, directly followed by enhanced internal (closed-system) degassing and\nassociated further pressure buildup.”\nComment 50: L 204: why eruption rates should increase? Please be careful to not end up in a purely\nspeculative discussion, which seems undermining an otherwise really nice study and database.\nThis is a thoughtful comment. We agree that increased eruption rates may be speculative, and have\nomitted this expression.\nComment 51: L 206...: rapid, catastrophc, highly explosive, ... please tone down.\nWe have expanded the respective section and provided more detail, and thereby slightly toned down\nparts of the discussion. We agree with removing the word “catastrophic”, but think the phrase “highly\nexplosive” is appropriate in this context, in line with published data and observations on the Kolumbo\n1650 eruption.\nComment 52: L 208: i do not understand why authors now speculate about bubble coalescence. Any\nsupport from the field?\nWe have provided more context to this section, in order to constrain the timescales involved in the\ntriggering of the highly explosive eruption phase. Concerning field evidence, we now refer to the very\nhigh vesicularity of the pumice in the cone, and to the occurrence of fine grained Kolumbo ash in nearby\nsurface sediments, both being evidence of very efficient fragmentation during the explosive events. In\nline with these observations, we cite laboratory decompression experiments of vesiculated melts, which\nshow that bubble coalescence is an important pre-requisite for the triggering of efficient syn-eruptive\nmagma fragmentation. We think the timescales involved in such bubble coalescence processes fit well\nwith the suggested overall scenario, and provide complementary evidence for the timescales involved.\nWith due respect, we cannot see that this line of evidence is speculative in the given context.\nComment 53: L 246: which several active volcanoes are these?\nThe text that directly follows this opening statement details examples of such active volcanoes: Kick’em\nJenny, HTHH, Myojinsho.\nComment 54: L 254: eruptions bore similarities... > is this english? I am not a native speaker, but this\nsounds incorrect.\nYes, we checked it and it’s correct English.\nComment 55: L 261: how large is the significance mathematically?\nWe are not talking about mathematical / statistical significance here. We are using the word “significant”\nto make clear that it is not a minor / insignificant hazard.\nComment 56: L 272-274: This is not fully correct. Years prior to the Anak Krakatau collapse, a scientific\npaper forecasted the direction, scale and threat of a sector collapse. The problem is more complex,\nwhere especially communication strategies and awareness is lacking. Please consider looking into the\nrelated literature before speculating.\nWe are aware of the scientific literature surrounding Anak Krakatau. We completely agree that the prob-\nlem is complex and requires effective communication and awareness. We also think that monitoring\nstrategies are required to be able to respond better to emerging hazards.\nIf we understand your point here correctly, we think you are not in agreement with our inclusion of\n“scientists” as a group that is unprepared. We think that scientists need to do more (i.e. monitoring) to\nbe better prepared for future emerging hazards. However, to simplify this whole sentence, and tone it\ndown a bit, we have changed the wording of the last two sentences to:\n\"Local populations are currently under-prepared for the threats posed by submarine eruptions\nand slope failures, as has been demonstrated by the recent 2018 sector collapse of Anak Krakatau\nand the 2022 HHTH eruption. We propose that new shore-line crossing monitoring strategies are\nrequired that are capable of being deployed as part of rapid response initiatives during volcanic\nunrest, and which enable real-time observation of slope movement.”\nComment 57: L 372: 372 Materials & Correspondence. For data enquiries, please contact Jens\nKarstens. I think this is NOT appropriate nowadays anymore. Please upload bathymetric data and ROV\nimages to supplementary or an accessible online database.\nWe have updated the data availability statement. We have uploaded the presented seismic profiles and\nthe AUV bathymetry to repositories. The uploading process for the latter is still in progress. The full 3D\nseismic dataset is currently in the process of being uploaded and will be available in two years.\nComment 58: Figure 1: A) Figs should read Fig. B) hard to read and small text. C) add scales of eleva-\ntion (or is it the same as in B)?), and make distance scale more visible. The label \"Deformed flank\"\nappears at a location of erosive gullies.\nWe have updated the figure accordingly\nComment 59: Figure 2: Very nice. Listric faults usually come with block wise and antithetic faults. Is\nthe small graben structure showing this; or why authors highlight outward-dipping faults only?\nThis is a good point, and something we gave thought to during our interpretation of the deformation of\nthe flank. However, after careful examination of the data, it became clear that we were not able to map\nout many individual faults with sufficient certainty between the detachment surface and the seafloor.\nRather, the data reveal distributed deformation, mainly in the form of internal folding and seafloor steps,\nwhich are the basis for our interpretation of compressional deformation of the flank. We think we would\nrisk “overinterpreting” the data if we attempt to speculate about antithetic faults and particular graben\nstructures. Rather, we prefer to take a broader view of the large-scale deformation of the flank.\nComment 60: Figure 3. Can the dimension of the dikes be estimated? How sure are authors this plane\nis the actual \"sliding plane\"? Can B, C and D images be located on the A map?\nThe interpretation of the sliding plane bases on our seismic interpretations. However, since the slide\nplane is partially covered by material (see 2c), we have changed the label to “Partially exposed slide\nplane” in the figure labels. We have added the locations of the photographs to the figure. Based on ROV\nvideo footage, the dykes have widths of 5 – 10 m.\nComment 61: Figure 5: the block diagrams lack important structural features from this work, such as\nthe decollement, surface faults and so on. I suggest to try having it less speculative, and more closely\nrelated to the actual findings of this manuscript.\nWe have added some more descriptive terms to the block diagrams to label the detachment surface and\ncompressional deformation between the detachment and the seafloor. This links this conceptual diagram\nbetter to the observations shown from seismic data earlier in the manuscript.\nReviewer #3 (Remarks to the Author):\nThe paper provides a very interesting investigation of the 1650 Kolumbo tsunamigenic eruption. Start-\ning from the analysis of high-resolution three-dimensional seismic data, the authors provide a novel\nhypothesis regarding the complex sequence of events that culminated in the 1650 explosion. The hy-\npothesis is validated by simulating the ensuing tsunami starting from three different generation mecha-\nnisms and by comparing the results with the available historical accounts on the tsunami features (po-\nlarity of the first arrival and maximum wave amplitudes at five different sites/areas). The conclusion\nthat the tsunami was likely generated by the combined effect of a submarine landslide along the\nnorthwestern flank of the volcano followed after few minutes by the explosion seems sound and well supported\nby data interpretation and tsunami simulations.\nSo, my opinion is that the paper deserves to be published.´I have nonetheless a few issues to raise, which\nI think could contribute to make the paper more complete.\nWe would like to thank the reviewer for the helpful comments and suggestions.\nAs a tsunami modeller, I am especially interested in some modelling details. I must admit I am not\nfamiliar with VolcFlow, but I guess it shares some common features with other numerical codes.\nComment 62: If applicable, what was the spatial resolution used for the numerical simulations?\nOur simulations were performed with a lateral resolution of 100 m. We have updated the description\nof the simulations and the used parameters in the method section:” The tsunami simulations were\nperformed with numerical simulations code VolcFlow (details in refs. refs. 27 – 30, 48). VolcFlow\nsimulates the slide as a fluid and couples the interaction between the slide and the water based on\na depth-averaged approximation on a topography-linked coordinate system. Volcflow applies a\nplastic behaviour with turbulence as rheology, which is primarily controlled by yield strength and\ndensity. The code uses general depth-averaged equations of mass and momentum conserva-\ntion22,44. The slide was defined by reconstructing a pre-slide topography (see Supplement S1),\nwhich was achieved by using the geometry of the remaining cone and constraints about the pre-\nslide geometry (i.e., that the cone breached the sea-surface) and mapping the detachment surface\nin the 3D seismic datasets as slide plane, which had to be converted into the time domain using a\nseismic velocity of 1.7 km/s; ref. 14). The simulations had a lateral resolution of 100 m and s sim-\nulations duration of 30 minutes. We performed 20 slide simulations using various density (1,250,\n1,500, 1,750 and 2,000 kg/m³) and yield strengths (5,000, 7,500, 10,000, 20,000 and 50,000 Pa) to\ntest the parameter space (see. Supplement 1). To simulate the effects of an explosion, we followed\nthe approach by Ulvrova et al. (2016) and assumed a radial-symmetric initial explosion-induced\nwater undulation for four different peak wave heights (100, 125, 150 and 240 m). Finally, we per-\nformed 20 simulations combining a slide and explosion using the same explosion-induced water\nundulations and five different time gaps between slide and explosion (1, 2, 3, 4, 5 minutes) com-\nbined with a slide with representative density of 1,500 kg/m³ and a yield strength of 7,500 Pa (as\ndescribed in ref. 23). For this, the initial wave field from the explosion-derived tsunami simulations\nwas added to the wave field of the landslide tsunami simulations at one specific time step (1, 2, 3,\n4, 5 minutes) and the code used this superimposed wave fields for the rest of the simulations. To\ncompare simulated wave heights with eyewitness accounts, we created maps showing the maxi-\nmum wave height as well as virtual tide gauges at locations, where direct tsunami observations\nare available. The virtual tide gauges were placed in shallow water (5-10 m and not at the coast-\nline) to allow analysing a potential sea retreat at each location.”.\nComment 63: For the landslide simulation, what kind of rheology was adopted? In understand you\nspecified density and yield strength, but this could apply to different rheologies.\nVolcflow applies a plastic behaviour with turbulence. We have added a statement to the method section\n(See comment 62).\nComment 64: In the depth averaged equations, are non-linear and/or dispersion terms accounted for in\nthis study?\nVolcflow does not account for dispersion. While dispersion may have a major effect for some wave field\nsimulations, it has only a minor effect for our simulations as the wavelength of the tsunami is large\ncompared to the relatively shallow water depth in the study area and as the tsunami source is close to\nthe analysed coastlines.\nComment 65: A delicate point regards the combined generation mechanism. The authors state: \"[...] to\nsimulate the effects of a combination of both source mechanisms, superimposing the wavefield of an\nexplosion onto that caused by flank deformation.\". Does this mean the two mechanisms were treated\nseparately and then the results summed together to obtain the combined effect? If this is true, then I\nthink this procedure is not appropriate for highly non-linear generation mechanisms like the ones considered.\nI ask the authors to comment on this.\nYes, this is an important point. While tsunami generation by the sliding mass is a continuous, long-term\n(several minutes) process, we consider the generation by the explosion as (quasi) instantaneous. We\ndefined the initial water undulation by the explosion following the approximation by Ulvrova et al.,\n2016. This wave field was added to the wave field of the landslide tsunami simulations at one specific\ntime step (e.g. after 240 seconds like in figure 4c), which we believe is justified by the assumed instan-\ntaneous nature of tsunami generation by the explosion. The code then continue using this superimposed\nwave field for the rest of the simulations. Therefore, our combined simulations are not the sum of the\nwave field of the slide and that of the explosion at every time step.\nComment 66: How are the coastal boundaries treated? From the inspection of the computed tide gauge-\nrecords, it looks like a minimum depth has been used, pointing at the idea that linear simulations were\nrun. Please clarify, taking also into account that, especially for the explosion, the tsunami generation\nmechanism is expected to be highly non-linear (see also my previous point).\nMoreover, I ask the authors to detail more the criterion adopted to establish the water elevation\nthreshold to assess the consistency with the historical accounts. In particular, in Sikinos the historical\ninformation regards an inundation extent of 240 m: how is this converted into maximum water\nelevation? If linear tsunami simulations are run and here non inundation is modelled, where are the\nmaximum elevation computed? Along the coastline with a minimum depth attached? In correspondence\nwith a selected isobath? Using observed run-up in the comparison with computed maximum water\nelevations could not be appropriate and my bias the consistency assessment. Can the authors be more\ndetailed on this aspect?\nWe have added a statement to the method section “The virtual tide gauges were placed in shallow\nwater (5-10 m and not at the coastline) to allow analysing a potential sea retreat at each location.”.\nAs mentioned, the explosion triggered tsunami could only be approximated using the approach by\nUlvrova et al., 2016, which does not reflect the non-linearity of the explosion. The Volcflow simulation\nallow inundation of the tsunami wave. The criticism regarding including the eyewitness accounts from\nSikinos into the analyses are fair considering the lateral resolution of only 100 m and the missing infor-\nmation, where exactly on Sikinos the water inundated for 240 m. While we still believe that the obser-\nvation of a significant inundation is worth to be included in the manuscript, we have updated the manu-\nscript indicating that that the inundation observation cannot be transferred into tsunami heights consid-\nering the limitations of the simulations: “The observed inundation of 240 m on Sikinos cannot di-\nrectly transferred to a run-up height due to simplified topography used in the simulations and the\nlack of precise location of the eyewitness account, but indicates that the southeastern coast of Si-\nkinos was affected by a tsunami with significant run-up height.”\nFew typos and possible improvements are listed hereafter.\nComment 67: Row 52: \"western coast of Santorini\": is it \"eastern coast of Santorini\"?\nYes, this correct. Thank you for spotting this. We changed the manuscript accordingly\nComment 68: Row 95: here the width of the crater is indicated in 2500 m (as in two 217), while at row\n47 it is of 1500 m. I am a bit confused.\nIt must be 2500 m. We have changed the manuscript accordingly.\nComment 69: Row 131: \"Krakatau\" instead of \"Kraktau\".\nWe have changed the manuscript accordingly.\nComment 70: Row 232: separate \"whichwas\".\nWe have changed the manuscript accordingly.\nComment 71: Row 282: \"Christiana\" instead of \"Christian\"?\nWe have changed the manuscript accordingly.\nComment 72: Figure 2: Correct \"Remant\" into \"Remnant\" in all three panels.\nThank you for spotting this. We have changed the manuscript accordingly.\nComment 73: Row 3512: (1,2,3,4,5 min).\nWe have changed the manuscript accordingly.\nComment 74: Supplement 2, Figures S5 - S26. In the caption, it would be desirable to summarise very\nbriefly the criteria used to assess the consistency with the historical accounts. Maybe you could add in\neach tide gauge record plot an horizontal line showing the imposed threshold in amplitude.\nThis is good idea. We have added following statement to the figure captions: “Threshold tsunami\nheights from eyewitness accounts used to evaluate the simulation results: 7.5 m at northern San-\ntorini, 5 m at Perissa, 5 m Kamari, 10 m at southern Ios and 10 m at Sikinos. A direct transfer of\ninundation observations to tsunami height for Sikinos is not possible and thus the Sikinos thresh-\nold has is less reliable compared to the direct tsunami height information available for the other\nlocations.”\nREVIEWERS' COMMENTS\nReviewer #2 (Remarks to the Author):\nI have read the revised version of the manuscript and also the rebuttal letter provided. Looking at these\ndocuments provided, i see that all points I raised have been addressed thoroughly.\nReviewer #3 (Remarks to the Author):\nI think the authors did a good job in revising the manuscript. All my comments and suggestions have\nbeen properly taken into account.\nI send only few suggestions for typo corrections and slight modifications.\nPage 1, row 40: correct “oberved” into “observed”\nPage 8, caption to Figure 1. Please add a sentence like: \"The cyan, red and purple lines indicate the\nposition of the profiles depicted in Fig. 3.\"\nPage 10, caption to Figure 3. Please add a sentence like: “The position of the three profiles is drawn in\nFig. 1.”\nPage 12, Figure 5, panel a). Correct “reconstrucation” into “reconstruction”. Panel b): correct\n“Topgraphy” into “Topography”.\nPage 15, rows 369-370: modify the sentence as “The tsunami simulations were performed with the\nnumerical code VolcFlow …”\nPage 15, row 378: delete “s simulations”\nPage 15, row 379: change “density” into “densities”\nPage 20: the last reference appears to be truncated and incomplete.\nBest regards,\nAlberto Armigliato"}]

Decision letter