Gianluca Sottili

Maars to calderas: end-members on a spectrum of explosive volcanic depressions

We discuss maar-diatremes and calderas as end-members on a spectrum of negative volcanic landforms (depressions) produced by explosive eruptions (note – we focus on calderas formed during explosive eruptions, recognizing that some caldera types are not related to such activity). The former are dominated by ejection of material during numerous discrete phreatomagmatic explosions, brecciation, and subsidence of diatreme fill, while the latter are dominated by subsidence over a partly evacuated magma chamber during sustained, magmatic volatile-driven discharge. Many examples share characteristics of both, including landforms that are identified as maars but preserve deposits from non-phreatomagmatic explosive activity, and ambiguous structures that appear to be coalesced maars but that also produced sustained explosive eruptions with likely magma reservoir subsidence. A convergence of research directions on issues related to magma-water interaction and shallow reservoir mechanics is an important avenue toward developing a unified picture of the maar-diatreme-caldera spectrum.

Geochemical fingerprints of volcanic materials: Identification of a pumice trade route from Pompeii to Rome

Geochemical investigations on samples of pumice and lava extracted from the mortars and concretes of the Forum of Caesar and the Forum and Markets of Trajan are pre- sented and integrated with previous analyses of lava samples from Rome and Pompeii, and of pumices from the Colosseum and the Dioclethians Bath, with the aim to identify the lithological provenance of these materi- als. Discrimination diagrams based on ratios of selected trace elements (i.e., Zr/Y, Nb/Y, Th/Ta, Nb/Zr) allow us to recognize the geo- chemical signature of the different volcanic regions of central Italy. These diagrams in- dicate that in the mortars of the Forum of Caesar and Forum of Trajan, the Roman builders integrated the scanty pumices from deposits of the Monti Sabatini Volcanic Dis- trict near Rome with others coming from the Vesuvius and Phlegrean Fields. Some of the pumices employed in the vaulted ceil- ings of these monuments display a peculiar geochemistry that has a unique correspon- dence with a pyroclastic deposit recovered in a borehole drilled on the southern fl anks of Vesuvius. Similarly, lava fl ows from this borehole display a different trace-element signature with respect to that of other coeval lava fl ows of the northern fl anks of Vesuvius, and it has a closer correspondence to that of the archaeological lava samples. These observations, integrated with historical and archaeological data, indicate that the Roman builders had a profound empirical knowl- edge of the physical properties of the volcanic rocks from different regions, and suggest that a systematic cultivation of lightweight volca- nic material occurred in the area of Pompeii for exportation to Rome and, likely, to other regions of the Mediterranean.

Assessing the volcanic hazard for Rome: 40Ar/39Ar and In‐SAR constraints on the most recent eruptive activity and present‐day uplift at Colli Albani Volcanic District

We present new 40Ar/39Ar data which allow us to refine the recurrence time for the most recent eruptive activity occurred at Colli Albani Volcanic District (CAVD) and constrain its geographic area. Time elapsed since the last eruption (36 kyr) overruns the recurrence time (31 kyr) in the last 100 kyr. New interferometric synthetic aperture radar data, covering the years 1993–2010, reveal ongoing inflation with maximum uplift rates (>2 mm/yr) in the area hosting the most recent (<200 ka) vents, suggesting that the observed uplift might be caused by magma injection within the youngest plumbing system. Finally, we frame the present deformation within the structural pattern of the area of Rome, characterized by 50 m of regional uplift since 200 ka and by geologic evidence for a recent (<2000 years) switch of the local stress-field, highlighting that the precursors of a new phase of volcanic activity are likely occurring at the CAVD.

Benford’s Law in Time Series Analysis of Seismic Clusters

Benford’s analysis is applied to the recurrence times of approximately 17,000 seismic events in different geological contexts of Italy over the last 6 years, including the Mt. Etna volcanic area and the seismic series associated with the destructive Mw 6.3, 2009 L’Aquila earthquake. A close conformity to Benford’s law and a power-law probability distribution for the recurrence times of consecutive events is found, as typical of random multiplicative processes. The application of Benford’s law to the recurrence event times in seismic series of specific seismogenic regions represents a novel approach, which enlarges the occurrence and relevance of Benford-like asymmetries, with implications on the physics of natural systems approaching a power law behaviour. Moreover, we propose that the shift from a close conformity of Benford’s law to Brownian dynamics, observed for time separations among non-consecutive events in the study seismic series, may be ruled by a periodical noise factor, such as the effects of Earth tides on seismicity tuning.

Parameterizing multi-vent activity at Stromboli Volcano (Aeolian Islands, Italy)

The crater terrace of Stromboli Volcano (Italy) hosts several active vents which have evolved and migrated through time within three main vent areas: south-west (SW), central (C), and north-east (NE). Frequent, jet-like explosions typically take place, episodically interrupted by larger-scale paroxysms, which can substantially modify the morphology of the crater terrace and vent geometries. However, the link between the time-space evolution of vent activity and the shallow conduit system are still a matter of debate. In this work, we analyze the vent position and explosion parameters (jet duration and geometry) of 4296 events at Stromboli in five 72-h-long time-windows between 2005 and 2009, as recorded by an infrared surveillance camera. Vent locations illustrate the resilience of the shallow conduit system, which controls explosive activity at different time scales and depths. At the shallowest depth, where slugs burst, conduit branching and merging determines the evolution of simultaneous or alternating twin vents, while vent shape and slug size control local explosion parameters. These processes show variability on an hourly to daily time scale. Below the depth of the slug burst, the conduit system feeding each vent area controls which specific vent will host the explosions and also, possibly, the size of the slugs. Several observations suggest that the C and SW vent areas may be connected at this depth. The deeper conduit system, common to all vent areas, sets the overall explosion rate of the volcano and maintains a balance of this rate between the NE and the combined SW and C vent areas.

Corrigendum: Maars to calderas: end-members on a spectrum of explosive volcanic depressions

Reason for Corrigendum: In the original article (Palladino et al., 2015), there was an error in Figure 1. The vertical axis of the qualitative plot reported erroneously “ratio of juvenile to lithic materials in deposits outside of depression”. The correct wording is as follows: “ratio of juvenile to total (i.e., juvenile+lithic) materials in deposits outside of depression”. In fact, as it was reported correctly in the text, the amount of juvenile material (i.e., scoria or pumice) deposited ouside the different types of explosive volcanic depressions increases from zero (i.e., no juvenile, all lithic products), as is the case of hydrothermal (phreatic) explosion craters, to become largely dominant over the lithic component in the case of ash flow deposits associated with large overpressure collapse calderas. The corrected Figure 1 appears below. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way.