Three-dimensional magnetotelluric modeling of Vulcano Island (Eolie, Italy) and its implications for understanding recent volcanic unrest.

This paper presents the results of an original short-period magnetotelluric survey performed on Vulcano Island (Italy). The obtained three-dimensional resistivity model details structures up to 2.5 km depth, hitherto unexplored. The La Fossa caldera area corresponds to a moderate resistive anomaly, which extends down to the resolved depth and likely represents a "conduit-like" structure along which magmatic fluids stall and ascend. Other resistive anomalies characterize volcanic edifices, craters, volcanic conduits, and/or eruptive fissures. In addition, the shallower hydrothermal system is detected as a conductive anomaly. Sharp resistivity contrasts generally characterize caldera faults. A main N‒S alignment characterizes the island sector, where considerable amounts of deep subsurface fluids accumulate and mix with the ascending magmas related to the most recent volcanic dynamics. The volcanological interpretation of such findings significantly contributes to understanding the geophysical and geochemical anomalies detected in the last year, which involved the Vulcano shallow hydrothermal system, highlighting the potential for possible hydrothermal/phreatic eruptive events.

The impact of pyroclastic density currents duration on humans: the case of the AD 79 eruption of Vesuvius.

Pyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome. They move away from the volcano at high speed, causing devastation. The impact is generally associated with flow dynamic pressure and temperature. Little emphasis has yet been given to flow duration, although it is emerging that the survival of people engulfed in a current strongly depends on the exposure time. The AD 79 event of Somma-Vesuvius is used here to demonstrate the impact of pyroclastic density currents on humans during an historical eruption. At Herculaneum, at the foot of the volcano, the temperature and strength of the flow were so high that survival was impossible. At Pompeii, in the distal area, we use a new model indicating that the current had low strength and low temperature, which is confirmed by the absence of signs of trauma on corpses. Under such conditions, survival should have been possible if the current lasted a few minutes or less. Instead, our calculations demonstrate a flow duration of 17 min, long enough to make lethal the breathing of ash suspended in the current. We conclude that in distal areas where the mechanical and thermal effects of a pyroclastic density currents are diminished, flow duration is the key for survival.

High-precision 14C and 40Ar/39Ar dating of the Campanian Ignimbrite (Y-5) reconciles the time-scales of climatic-cultural processes at 40 ka.

The Late Pleistocene Campanian Ignimbrite (CI) super-eruption (Southern Italy) is the largest known volcanic event in the Mediterranean area. The CI tephra is widely dispersed through western Eurasia and occurs in close stratigraphic association with significant palaeoclimatic and Palaeolithic cultural events. Here we present new high-precision 14C (34.29 ± 0.09 14C kyr BP, 1σ) and 40Ar/39Ar (39.85 ± 0.14 ka, 95% confidence level) dating results for the age of the CI eruption, which substantially improve upon or augment previous age determinations and permit fuller exploitation of the chronological potential of the CI tephra marker. These results provide a robust pair of 14C and 40Ar/39Ar ages for refining both the radiocarbon calibration curve and the Late Pleistocene time-scale at ca. 40 ka. In addition, these new age constraints provide compelling chronological evidence for the significance of the combined influence of the CI eruption and Heinrich Event 4 on European climate and potentially evolutionary processes of the Early Upper Palaeolithic.

Experimental investigations on the explosivity of steam-driven eruptions: A case study of Solfatara volcano (Campi Flegrei).

Steam-driven eruptions, both phreatic and hydrothermal, expel exclusively fragments of non-juvenile rocks disintegrated by the expansion of water as liquid or gas phase. As their violence is related to the magnitude of the decompression work that can be performed by fluid expansion, these eruptions may occur with variable degrees of explosivity. In this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam-driven explosive energy. A series of fine-grained heterogeneous tuffs from the Campi Flegrei caldera were investigated for their petrophysical properties. The rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs. Our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy. Overall, the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple (Argon) gas expansion and may produce a higher amount of fine material even under partially saturated conditions. The energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles. Moreover, weak and low permeability rocks yield a maximum fine fraction. Using experiments to unravel the energetics of steam-driven eruptions has yielded estimates for several parameters controlling their explosivity. These findings should be considered for both modeling and evaluation of the hazards associated with steam-driven eruptions.