The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the strike of the crack modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 × 105 and 3.6 × 105 m3, respectively, meaning that 1.5 × 105 m3 of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥ 1014 J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 year. Although the ejecta mass of the 2018 phreatic eruption was small, the eruption at Mt. Motoshirane was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 × 107 kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

Modeling Volcanic Debris Clouds

How does a large volcanic cloud get into the stratosphere? Scientists model how volcanic debris injected into the lower stratosphere can be lofted high into the middle stratosphere.

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu–Shirane volcano, Japan: Eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the crack azimuth modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 * 10 5 and 3.6 * 10 5 m 3 , respectively, meaning that 1.5 * 10 5 m 3 of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥10 14 J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 yr. Although the ejecta mass of the 2018 phreatic eruption was small, the 2018 MPCG eruption was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 * 10 7 kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

Dual-Wavelength Polarimetric Lidar Observations of the Volcanic Ash Cloud Produced During the 2016 Etna Eruption

Lidar observations are very useful to analyse dispersed volcanic clouds in the troposphere mainly because of their high range resolution, providing morphological as well as microphysical (size and mass) properties. In this work, we analyse the volcanic cloud of 18 May 2016 at Mt. Etna, in Italy, retrieved by polarimetric dual-wavelength Lidar measurements. We use the AMPLE (Aerosol Multi-Wavelength Polarization Lidar Experiment) system, located in Catania, about 25 km from the Etna summit craters, pointing at a thin volcanic cloud layer, clearly visible and dispersed from the summit craters at the altitude between 2 and 4 km and 6 and 7 km above the sea level. Both the backscattering and linear depolarization profiles at 355 nm (UV, ultraviolet) and 532 nm (VIS, visible) wavelengths, respectively, were obtained using different angles at 20°, 30°, 40° and 90°. The proposed approach inverts the Lidar measurements with a physically based inversion methodology named Volcanic Ash Lidar Retrieval (VALR), based on Maximum-Likelihood (ML). VALRML can provide estimates of volcanic ash mean size and mass concentration at a resolution of few tens of meters. We also compared those results with two methods: Single-variate Regression (SR) and Multi-variate Regression (MR). SR uses the backscattering coefficient or backscattering and depolarization coefficients of one wavelength (UV or VIS in our cases). The MR method uses the backscattering coefficient of both wavelengths (UV and VIS). In absence of in situ airborne validation data, the discrepancy among the different retrieval techniques is estimated with respect to the VALR ML algorithm. The VALR ML analysis provides ash concentrations between about 0.1 ?g/m3 and 1 mg/m3 and particle mean sizes of 0.1 ?m and 6 ?m, respectively. Results show that, for the SR method differences are less than <10%, using the backscattering coefficient only and backscattering and depolarization coefficients. Moreover, we find differences of 20%--30% respect to VALR ML, considering well-known parametric retrieval methods. VALR algorithms show how a physics-based inversion approaches can effectively exploit the spectral-polarimetric Lidar AMPLE capability.

Long-lived ultra-fine ash particles within the Pinatubo volcanic aerosol cloud and their potential impact on its global dispersion and radiative forcings

&lt;p&gt;Volcanic aerosol simulations with interactive stratospheric aerosol models mostly neglect ash particles, due to a general assumption they sediment out of the volcanic plume within the first few weeks and have limited impacts on the progression of the volcanic aerosol cloud (Niemeier et al., 2009).&amp;#160;&lt;/p&gt; &lt;p&gt;However, observations, such as ground-based and airborne lidar (Vaughan et al., 1994; Browell et al., 1993), along with impactor measurements (Pueschel et al., 1994) in the months after the Mount Pinatubo eruption suggest the base of the aerosol cloud contained ash particles coated in sulphuric acid for around 9 months after the eruption occurred.&amp;#160; Impactor measurements from flights following the 1963 Agung and 1982 El Chichon eruptions also show ash remained present for many months after the eruption (Mossop, 1964; Gooding et al., 1983).&amp;#160; &lt;br /&gt;&lt;br /&gt;More recently, satellite, in situ and optical particle counter measurements after the 2014 Mount Kelud eruption showed ash particles ~0.3 &amp;#181;m in size accounting for 20-28% of the volcanic cloud AOD 3 months following the eruption (Vernier et al., 2016; Deshler, 2016).&amp;#160; This evidence suggests that sub-micron ash particles may persist for longer in the atmosphere than is often assumed.&amp;#160;&lt;/p&gt; &lt;p&gt;We explore how the presence of these sub-micron ash particles affects the progression of a major tropical volcanic aerosol cloud, showing results from simulations with a new configuration of the composition-climate model UM-UKCA, adapted to co-emit fine-ash alongside SO2.&amp;#160;&amp;#160; In the UM-UKCA simulations, internally mixed ash-sulphuric particles are transported within the existing coarse-insoluble mode of the GLOMAP-mode aerosol scheme. &lt;br /&gt;&lt;br /&gt;Size fractions of 0.1, 0.316 and 1 &amp;#181;m diameter ash were tested for the 1991 Mount Pinatubo eruption with an ultra-fine ash mass co-emission of 0.05 and 0.5 Tg, based on 0.1% and 1% of an assumed fine ash emission of 50Tg. &amp;#160;Whereas the 0.316 and 1 &amp;#181;m sized particles sedimented out of the stratosphere within the first 90 days after the eruption, the 0.1 &amp;#181;m persisted within the lower portion of volcanic cloud for ~9 months, &amp;#160;retaining over half its original mass (0.035 Tg) February 1992.&amp;#160;&lt;/p&gt; &lt;p&gt;We investigate model experiments with different injection heights for the co-emitted SO2 and ash, analysing the vertical profile of the ultra-fine ash compared to the sulphate aerosol, and explore the effects on the volcanic aerosol cloud in terms of its overall optical depth and vertical profile of extinction.&lt;/p&gt; &lt;p&gt;The analysis demonstrates that although fine-ash is more persistent than previous modelling studies suggest, these particles have only modest impacts with the radiative heating effect the dominant pathway, with the sub-micron particles not scavenging sufficiently.&amp;#160;&amp;#160;&lt;/p&gt; &lt;p&gt;Future work will explore simulations with a further adapted UM-UKCA model with an additional &amp;#8220;super-coarse&amp;#8221; insoluble mode resolving the super-micron ash, then both components of the fine-ash resolved to test the magnitude of sulfate scavenging effect.&amp;#160;&lt;/p&gt;

Measurement Report: Lidar measurements of stratospheric aerosol following the 2019 Raikoke and Ulawun volcanic eruptions

At 18:00 UTC on 21 June 2019 the Raikoke volcano in the Kuril islands began a large-magnitude explosive eruption, sending a plume of ash and sulfur dioxide into the stratosphere. A Raman lidar system at Capel Dewi Atmospheric Observatory, UK, was deployed to measure the vertical extent and optical depth of the volcanic aerosol cloud following the eruption. The elastic channel at 355 nm allowed measurements up to 25 km, but the Raman channel was only sensitive to the troposphere. Therefore, retrievals of backscatter ratio profiles from the raw backscatter measurements required aerosol-free profiles derived from nearby radiosondes and allowance for aerosol extinction using a lidar ratio of 40–50 sr. Small amounts of aerosol were measured prior to the arrival of the volcanic cloud (27 June–5 July 2019), from pyroconvection over Canada. Model simulations by de Leeuw et al. (2020) and Kloss et al. (2020) show that volcanic ash may have reached Europe from 1 July onwards and was certainly present over the UK after 10 July. The lidar detected a thin layer at an altitude of 14 km late on 3 July, with the first detection of the main aerosol cloud on 13 July. In this initial period the aerosol was confined below 16 km, but eventually the cloud extended to 20.5 km. A sustained period of clearly enhanced stratospheric aerosol optical depths began in early August, with a maximum value (at 355 nm) around 0.05 in mid-August and remaining above 0.02 until early November. Thereafter, optical depths decayed to around 0.01 by the end of 2019 and remained around that level until May 2020. The altitude of peak backscatter varied considerably (between 14 and 18 km) but was generally around 15 km. However, on one notable occasion on 25 August 2019, a layer around 300 m thick with peak lidar backscatter ratio around 1.5 was observed as high as 21 km.

Simulation of ash clouds after a Laacher See-type eruption

Dated to approximately 13 000 years ago, the Laacher See (East Eifel volcanic zone) eruption was one of the largest midlatitude Northern Hemisphere volcanic events of the Late Pleistocene. This eruptive event not only impacted local environments and human communities but probably also affected Northern Hemispheric climate. To better understand the impact of a Laacher See-type eruption on NH circulation and climate, we have simulated the evolution of its fine ash and sulfur cloud with an interactive stratospheric aerosol model. Our experiments are based around a central estimate for the Laacher See aerosol cloud of 15 Tg of sulfur dioxide (SO2) and 150 Tg of fine ash, across the main eruptive phases in May and a smaller one in June with 5 Tg SO2 and 50 Tg of fine ash. Additional sensitivity experiments reflect the estimated range of uncertainty of the injection rate and altitude and assess how the solar-absorptive heating from the fine ash emitted in the first eruptive phase changed the volcanic clouds' dispersion. The chosen eruption dates were determined by the stratospheric wind fields to reflect the empirically observed ash lobes as derived from geological, paleoecological and archeological evidence linked directly to the prehistoric Laacher See eruption. Whilst our simulations are based on present-day conditions, and we do not seek to replicate the climate conditions that prevailed 13 000 years ago, we consider our experimental design to be a reasonable approximation of the transport pathways in the midlatitude stratosphere at this time of year. Our simulations suggest that the heating of the ash plays an important role for the transport of ash and sulfate. Depending on the altitude of the injection, the simulated volcanic cloud begins to rotate 1 to 3 d after the eruption. This mesocyclone, as well as the additional radiative heating of the fine ash, then changes the dispersion of the cloud itself to be more southward compared to dispersal estimated without fine ash heating. This ash-cloud-generated southerly migration process may at least partially explain why, as yet, no Laacher See tephra has been found in Greenland ice cores. Sulfate transport is similarly impacted by the heating of the ash, resulting in stronger transport to low latitudes, later arrival of the volcanic cloud in the Arctic regions and a longer lifetime compared to cases without injection of fine ash. Our study offers new insights into the dispersion of volcanic clouds in midlatitudes and addresses a likely behavior of the ash cloud of the Laacher See eruption that darkened European skies at the end of the Pleistocene. In turn, this study can also serve as significant input for scenarios that consider the risks associated with re-awakened volcanism in the Eifel.

Volcanic ash detection and retrievals using SLSTR. Test case: 2019 Raikoke eruption

&lt;p&gt;When an eruption event occurs it is necessary to accurately and rapidly determine the position and evolution during time of the volcanic cloud and its parameters (such as Aerosol Optical Depth-AOD, effective radius-Re and mass-Ma of the ash particles), in order to ensure the aviation security and the prompt management of the emergencies.&lt;/p&gt;&lt;p&gt;Here we present different procedures for volcanic ash cloud detection and retrieval using S3 SLSTR (Sentinel-3 Sea and Land Surface Temperature Radiometer) data collected the 22 June at 00:07 UTC by the Sentinel-3A platform during the Raikoke (Kuril Islands) 2019 eruption.&lt;/p&gt;&lt;p&gt;The volcanic ash detection is realized by applying an innovative machine learning based algorithm, which uses a MultiLayer Perceptron Neural Network (NN) to classify a SLSTR image in eight different surfaces/objects, distinguishing volcanic and weather clouds, and the underlying surfaces. The results obtained with the NN procedure have been compared with two consolidated approaches based on an RGB channels combination in the visible (VIS) spectral range and the Brightness Temperature Difference (BTD) procedure that exploits the thermal infrared (TIR) channels centred at 11 and 12 microns (S8 and S9 SLSTR channels respectively). The ash volcanic cloud is correctly identified by all the models and the results indicate a good agreement between the NN classification approach, the VIS-RGB and BTD procedures.&lt;/p&gt;&lt;p&gt;The ash retrieval parameters (AOD, Re and Ma) are obtained by applying three different algorithms, all exploiting the volcanic cloud &amp;#8220;mask&amp;#8221; obtained from the NN detection approach. The first method is the Look Up Table (LUT&lt;sub&gt;p&lt;/sub&gt;) procedure, which uses a Radiative Transfer Model (RTM) to simulate the Top Of Atmosphere (TOA) radiances in the SLSTR thermal infrared channels (S8, S9), by varying the aerosol optical depth and the effective radius. The second algorithm is the Volcanic Plume Retrieval (VPR), based on a linearization of the radiative transfer equation capable to retrieve, from multispectral satellite images, the abovementioned parameters. The third approach is a NN model, which is built on a training set composed by the inputs-outputs pairs TOA radiances vs. ash parameters. The results of the three retrieval methods have been compared, considering as reference the LUT&lt;sub&gt;p&lt;/sub&gt; procedure, since that it is the most consolidated approach. The comparison shown promising agreement between the different methods, leading to the development of an integrated approach for the monitoring of volcanic ash clouds using SLSTR.&lt;/p&gt;&lt;p&gt;The results presented in this work have been obtained in the sphere of the VISTA (Volcanic monItoring using SenTinel sensors by an integrated Approach) project, funded by ESA and developed within the EO Science for Society framework [https://eo4society.esa.int/projects/vista/].&lt;/p&gt;

Investigation on flight level contamination using volcanic SO2 plume and cloud top height satellite products

&lt;p&gt;Volcanic emission is a major risk for air traffic. Flying through a volcanic cloud can have a strong impact on engines (damage caused by ash and/or sulphur dioxide &amp;#8211; SO&lt;sub&gt;2&lt;/sub&gt;) and persons. The knowledge of the height of the volcanic plume is indeed essential for pilots, airlines and passengers.&lt;/p&gt;&lt;p&gt;In this presentation, we study recent volcanic emissions to illustrate the difficulty for obtaining information about the height of the SO&lt;sub&gt;2&lt;/sub&gt; plume in a form relevant to aviation. Our study uses satellite data products. We consider SO&lt;sub&gt;2&lt;/sub&gt; layer height from TROPOMI (UV-vis hyperspectral sensor on board S5P, a polar orbiting platform), as shown by SACS (Support to Aviation Control Service), combined with cloud top observations (from the same sensors or from geostationary broadband imagers) to determine the minimum SO&lt;sub&gt;2&lt;/sub&gt;-cloud height. This is a validation which is of interest to aviation.&lt;/p&gt;&lt;p&gt;The flight level, not the km, is the measure, the unit for expressing height during cruise flight used on board by the pilots to ensure safe vertical separation between aircraft, despite natural local variations in atmospheric air pressure and temperature. Thus, it is critical to provide the corresponding SO&lt;sub&gt;2&lt;/sub&gt; contamination expressed as flight levels. Our study will focus on this conversion that is one item currently being developed in the frame of ALARM H2020 project (https://alarm-project.eu) and SACS early warning system (https://sacs.aeronomie.be) in the creation of NetCDF alert products.&lt;/p&gt;