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Sudden hydrothermal eruptions occur in many volcanic settings and may include high-energy explosive phases. Ballistics launched by such events, together with ash plumes and pyroclastic density currents, generate deadly proximal hazards. The violence of hydrothermal eruptions (or explosive power) depends on the energy available within the driving-fluids (gas or liquid), which also influences the explosive mechanisms, volumes, durations, and products of these eruptions. Experimental studies in addition to analytical modeling were used here to elucidate the fragmentation mechanism and aspects of energy balance within hydrothermal eruptions. We present results from a detailed study of recent event that occurred on the 6th of August 2012 at Upper Te Maari within the Tongariro volcanic complex (New Zealand). The eruption was triggered by a landslide from this area, which set off a rapid stepwise decompression of the hydrothermal system. Explosive blasts were directed both westward and eastward of the collapsed area, with a vertical ash plume sourced from an adjacent existing crater. All explosions ejected blocks on ballistic trajectories, hundreds of which impacted New Zealand's most popular hiking trail and a mountain lodge, 1.4 km from the explosion locus. We have employed rocks representative of the eruption source area to perform rapid decompression experiments under controlled laboratory conditions that mimic hydrothermal explosions under controlled laboratory conditions. An experimental apparatus for 34 by 70 mm cylindrical samples was built to reduce the influence of large lithic enclaves (up to 30 mm in diameter) within the rock. The experiments were conducted in a temperature range of 250 °C–300 °C and applied pressure between 4 MPa and 6.5 MPa, which span the range of expected conditions below the Te Maari crater. Within this range we tested rapid decompression of pre-saturated samples from both liquid-dominated conditions and the vapor-dominated field. Further, we tested dry samples at the same pressure and temperature conditions. Results showed that host rock lithology and state of the interstitial fluid was a major influence on the fragmentation and ejection processes, as well as the energy partitioning. Clasts were ejected with velocities of up to 160 m/s as recorded by high-speed camera. In addition to rare large clasts (analogous to ballistics), a large amount of fine and very fine (<63 μm) ash was produced in all experiments. The efficiency of transformation of the total explosive energy into fragmentation energy was estimated between 10 to 15%, depending on the host rock lithology, while less than 0.1% of this was converted into kinetic energy. Our results suggest that liquid-to-vapor (flashing) expansion provides an order of magnitude higher energy release than steam expansion, which best explains the dynamics of the westward (and most energetic) directed blast at Te Maari. Considering the steam flashing as the primary energy source, the experiments suggested that a minimum explosive energy of 7 × 10 10 to 2 × 10 12 J was involved in the Te Maari blast. Experimental studies under controlled conditions, compared closely to a field example are thus highly useful in providing new insights into the energy release and hazards associated with eruptions in hydrothermal areas. [ABSTRACT FROM AUTHOR]

The ballistic ejection of blocks during explosive eruptions constitutes a major hazard near active volcanoes. Fields of ballistic clasts can provide important clues towards quantifying the energy, dynamics and directionality of explosive events, but detailed datasets are rare. During the 6 August 2012 hydrothermal eruption of Upper Te Maari (Tongariro), New Zealand, three explosions occurred in rapid succession within less than 20 s. The first two produced laterally-directed pyroclastic density currents (PDC), and the final vertical explosion generated an ash plume. Each of these explosions was associated with the ejection of ballistic blocks. We present detailed maps of the resulting 5.1 km 2 block impact field and the distribution of the > 2200 impact craters with diameters > 2.5 m. There are two distinct regions of high crater concentration, where crater densities reach more than six times the average background density. These occur at distances of 500–700 m east and 1000–1350 west of a 430-m-long fissure that was created during the eruption. The high-density fields are characterized by a narrow radial spread of < 45° and are located along the proximal transport direction of the pyroclastic density currents. A provenance analysis of ballistic blocks allowed us to reconstruct two different eruptive vents for the explosions. The first two laterally-directed explosions were sourced from the fissure, while the third explosion occurred through the pre-existing Upper Te Maari Crater, generating a roughly axisymmetric shower of ballistics. Stratigraphic relationships between impact craters, PDC and fall deposits suggest that the ballistic blocks were initially coupled with the rapidly expanding gas–particle mixtures that produced the PDCs. Ballistic trajectory modeling, reproducing the lateral extent and main impact density pattern of the western impact field, allows estimation of the vertical expansion angle of the second and largest explosion. The calculations show that the largest proportion of the explosion energy was strongly focused as a narrow and extremely shallow (from − 3 to 15° from the horizontal) laterally expanding hydrothermal blast. The results presented here constitute an important data set for ballistic hazard assessment at Tongariro volcano and they can provide further clues towards better understanding highly energetic laterally directed volcanic explosions at similar hydrothermal fields. [ABSTRACT FROM AUTHOR]

Simple Summary: Cetacean strandings are frequent in occurrence and are likely to become even more common globally because of the effects of escalating anthropogenic activities. Due to the compromised state of stranded animals, euthanasia is often recommended or required. However, current knowledge and implementation of euthanasia methods remain highly variable, with limited data on the practicalities and welfare impacts of procedures. This study sought to evaluate the available published data on cetacean euthanasia in order to highlight significant knowledge gaps and provide direction to improve the welfare of stranded cetaceans. Data from the peer-reviewed literature and published reports were analysed, and significant knowledge gaps highlighted. Two main euthanasia methods, chemical and ballistics, were reported, with few details provided on the specific application of these. Few data were available about time to death/insensibility, parameters commonly required to assess the welfare impacts of killing methods. Overall, the findings highlight the lack of available information on cetacean euthanasia and suggest avenues for future work to improve welfare through the use of appropriate methods and increased data collection. The compromised state of stranded cetaceans means that euthanasia is often required. However, current knowledge and implementation of euthanasia methods remain highly variable, with limited data on the practicalities and welfare impacts of procedures. This study evaluated the available published data on cetacean euthanasia, highlighting knowledge gaps and providing direction to improve stranded cetacean welfare. A total of 2147 peer-reviewed articles describing marine mammal euthanasia were examined. Of these 3.1% provided details on the method used, with 91% employing chemical methods. Two countries, the United Kingdom (UK) and New Zealand (NZ), provided euthanasia reports to the International Whaling Commission (IWC) between 2007 and 2020. Methods employed were reported for 78.3% and 100% of individual cetaceans euthanised in the UK and NZ, respectively. In the UK, chemical euthanasia was most common (52%), whilst in NZ only ballistics methods were used. Few data were available about time to death/insensibility (TTD); 0.5% of peer-reviewed articles provided TTD, whilst TTD was reported for 35% of individuals in the UK and for 98% in NZ. However, IWC reports lacked detail on how death/insensibility were assessed, with multiple individuals "presumed instantly" killed. Overall, the findings highlight the lack of available information on cetacean euthanasia, and suggest increased data collection and the application of appropriate methods to improve welfare. [ABSTRACT FROM AUTHOR]

Breccia-filled eruption conduits are dynamic systems where pressures frequently exceed critical thresholds, generating earthquakes and transmitting fluids. To assess the dynamics of breccia-filled conduits, we examine lava, ash tuff, and hydrothermal breccia ballistics with varying alteration, veining, fractures, and brecciation ejected during the 27 April 2016 phreatic eruption of Whakaari/White Island. We measure connected porosity, strength, and permeability with and without tensile fractures at a range of confining pressures. Many samples are progressively altered with anhydrite, alunite, and silica polymorphs. The measurements show a large range of connected porosity, permeability, and strength. In contrast, the cracked samples show a consistently high permeability. The cracked altered samples have a permeability more sensitive to confining pressure than the unaltered samples. The permeability of our altered ballistics is lower than surface rocks of equivalent porosity, illustrating that mineral precipitation locally blocked pores and cracks. We surmise that alteration within the conduit breccia allows cracks to form, open and close, in response to pore pressure and confining pressure, providing a mechanism for frequent and variable fluid advection pulses to the surface. This produces temporally and spatially variable geophysical and geochemical observations and has implications for volcano monitoring for any volcano system with significant hydrothermal activity. [ABSTRACT FROM AUTHOR]