Search

We present an exposure analysis of infrastructure and lifeline to tephra fallout for a future large-scale explosive eruption of Sakurajima volcano. An eruption scenario is identified based on the field characterization of the last subplinian eruption at Sakurajima and a review of reports of the eruptions that occurred in the past six centuries. A scenario-based probabilistic hazard assessment is performed using the Tephra2 model, considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions. A quantitative exposure analysis of infrastructures and lifelines is presented primarily using open-access data. The post-event impact assessment of Magill et al. (Earth Planets Space 65:677-698, 2013) after the 2011 VEI 2 eruption of Shinmoedake is used to discuss the vulnerability and the resilience of infrastructures during a future large eruption of Sakurajima. Results indicate a main eastward dispersal, with longer eruption durations increasing the probability of tephra accumulation in proximal areas and reducing it in distal areas. The exposure analysis reveals that 2300 km of road network, 18 km of urban area, and 306 km of agricultural land have a 50% probability of being affected by an accumulation of tephra of 1 kg/m. A simple qualitative exposure analysis suggests that the municipalities of Kagoshima, Kanoya, and Tarumizu are the most likely to suffer impacts. Finally, the 2011 VEI 2 eruption of Shinmoedake demonstrated that the already implemented mitigation strategies have increased resilience and improved recovery of affected infrastructures. Nevertheless, the extent to which these mitigation actions will perform during the VEI 4 eruption presented here is unclear and our hazard assessment points to possible damages on the Sakurajima peninsula and the neighboring municipality of Tarumizu. [ABSTRACT FROM AUTHOR]

Pyroclastic density currents (PDCs) can have devastating impacts on urban settlements, due to their dynamic pressure and high temperatures. Our degree of understanding of the interplay between these hot currents and the affected infrastructures is thus fundamental not only to implement our strategies for risk reduction, but also to better understand PDC dynamics. We studied the temperature of emplacement of PDC deposits that destroyed and buried the Villa dei Papiri, an aristocratic Roman edifice located just outside the Herculaneum city, during the AD79 plinian eruption of Mt Vesuvius (Italy) by using the thermal remanent magnetization of embedded lithic clasts. The PDC deposits around and inside the Villa show substantial internal thermal disequilibrium. In areas affected by convective mixing with surface water or with collapsed walls, temperatures average at around 270 °C (min 190 °C, max 300 °C). Where the deposits show no evidence of mixing with external material, the temperature is much higher, averaging at 350 °C (min 300 °C; max 440 °C). Numerical simulations and comparison with temperatures retrieved at the very same sites from the reflectance of charcoal fragments indicate that such thermal disequilibrium can be maintained inside the PDC deposit for time-scales well over 24 hours, i.e. the acquisition time of deposit temperatures for common proxies. We reconstructed in detail the history of the progressive destruction and burial of Villa dei Papiri and infer that the rather homogeneous highest deposit temperatures (average 350 °C) were carried by the ash-sized fraction in thermal equilibrium with the fluid phase of the incoming PDCs. These temperatures can be lowered on short time- (less than hours) and length-scales (meters to tens of meters) only where convective mixing with external materials or fluids occurs. By contrast, where the Villa walls remained standing the thermal exchange was only conductive and very slow, i.e. negligible at 50 cm distance from contact after 24 hours. We then argue that the state of conservation of materials buried by PDC deposits largely depends on the style of the thermal interactions. Here we also suggest that PDC deposit temperatures are excellent proxies for the temperatures of basal parts of PDCs close to their depositional boundary layer. This general conclusion stresses the importance of mapping of deposit temperatures for the understanding of thermal processes associated with PDC flow dynamics and during their interaction with the affected environment. [ABSTRACT FROM AUTHOR]

The Ohakune Volcanic Complex is a late Pleistocene tuff ring – scoria/spatter cone complex located south of Ruapehu volcano. This small-volume volcano consists of an outer E-W elongated compound tuff ring edifice, three inner scoria-spatter cones and further volcanic depressions, located on the Ohakune Fault. We quantified accurately the variations of the eruptive styles and processes through time by systematic sampling of key stratigraphic marker beds at proximal and distal locations, and the determination of grain size distribution, componentry, density and vesicularity. Using a Digital Terrain Model coupled with stratigraphic data, we also determined the spatial distribution and volume of each identified unit and individual edifices within the Ohakune Volcanic Complex. Activity began with a shallow phreatomagmatic phase characterized by an almost continuous generation of a low eruptive column, accompanied by wet pyroclastic density currents, together with the ejection of juvenile fragments and accidental lithics from the surrounding country rocks. Subsequent activity was dominated by a variety of Strombolian eruptions exhibiting differing intensities that were at times disrupted by phreatic blasts or phreatomagmatic explosions due to the interaction with external water and/or sudden changes in magma discharge rate. At least three major vent-shifting events occurred during the eruption, which is demonstrated by the truncation of the initial tuff ring and the infilling of the truncated area by several coarse grained surge units. Our study indicates that approx. 12 × 10 6 m 3 DRE magma erupted within maximum 2.5 to 5 months through multiple vents. The erupted magma ascended from a depth of 16–18 km, and reached the surface within approximately 50 h. Alternating eruption styles, frequent vent-shifting and a variety of emplacement mechanisms inferred from the deposits of the Ohakune Volcanic Complex demonstrate the unpredictable nature of small-volume volcanism, contributing to our understanding of hazards attributed to this type of activity. Future small-volume eruptions within the Taupo Volcanic Zone may be of similar nature. [ABSTRACT FROM AUTHOR]

A hazardous gas eruption from two very close shallow boreholes occurred near the Fiumicino International Airport of Roma (Italy) from August to December 2013. The erupted gas was mostly CO 2 of deep origin and gas output was high and sustained over time reaching values of nearly 20 t day − 1 . After 3 months, the gas flux was still above 5 t day − 1 and was only stopped in December 2013 by long and expensive works of closure of the boreholes. The gas eruption was uncommon as being associated with the building of two mud volcanoes. This style of sustained deep CO 2 eruptions contrasts with the more common short-lived eruptions of shallow biogenic methane-dominated gas pockets. In this work, we present the chronology of the event, the results of geological, geochemical, and geophysical monitoring and a numerical modeling. We propose that the August–December 2013 sustained and prolonged event does not relate to the simple degassing of a shallow, isolated pocket of gas. On the contrary, it reflects very specific conditions in a shallow reservoir (hosted in a 10 m thick gravel layer at − 40 m within the Tiber river delta deposits), related to the interplay between the total pressure and the fraction of free CO 2 initially present, across very narrow value ranges around 0.59 MPa and 0.18, respectively. The coexistence of short-lived and long-lived eruptions from the same reservoir suggest that these conditions are not achieved everywhere in the gas reservoir, despite its homogeneous properties. This consideration implies either a pressure compartmentalization of the reservoir, or the occurrence of a transient, possibly associated with an impulsive release of gas from greater depths. The involvement of deeper and larger gas reservoirs connected along faults is evidenced by geophysical investigations. This conceptual model bears significant implications for gas hazard studies. [ABSTRACT FROM AUTHOR]