Volcanic eruptions from ghost magma chambers

Recent studies have proposed that magma reservoirs crystallized to a virtually rigid crystal-mush can be partially remelted by diffusion of hot fluids. We show that for a crystal mush with the composition of a K-trachyte from the Campanian Ignimbrite (CI) Eruption, remelting can occur without a significant increase of the magma temperature, but simply by diffusion of H2O by the magmatic gases feeding the system. The CI origin is not the issue here, but rather the chemical and physical behavior of an almost solidified magma mass left over in a reservoir after a major eruption. To test our hypothesis, we run high pressure/high temperature laboratory experiments to study the kinetics of water diffusion, together with thermodynamics and fluid diffusion modelling. For small diffusivities, or large diffusion time, the remelting mechanism proposed above needs to be replaced by other processes as gas percolation or intrusion of a magmatic mass

Earth's rotation variability triggers explosive eruptions in subduction zones

The uneven Earth’s spinning has been reported to affect geological processes, i.e. tectonism, seismicity and volcanism, on a planetary scale. Here, we show that changes of the length of day (LOD) influence eruptive activity at subduction margins. Statistical analysis indicates that eruptions with volcanic explosivity index (VEI) ≥3 alternate along oppositely directed subduction zones as a function of whether the LOD increases or decreases. In particular, eruptions in volcanic arcs along contractional subduction zones, which are mostly E- or NE-directed, occur when LOD increases, whereas they are more frequent when LOD decreases along the opposite W- or SW-directed subduction zones that are rather characterized by upper plate extension and back-arc spreading. We find that the LOD variability determines a modulation of the horizontal shear stresses acting on the crust up to 0.4 MPa. An increase of the horizontal maximum stress in compressive regimes during LOD increment may favour the rupture of the magma feeder system wall rocks. Similarly, a decrease of the minimum horizontal stress in extensional settings during LOD lowering generates a larger differential stress, which may enhance failure of the magma-confining rocks. This asymmetric behaviour of magmatism sheds new light on the role of astronomical forces in the dynamics of the solid Earth

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

CO2-crystal wettability in potassic magmas. Implications for eruptive dynamics in light of experimental evidence for heterogeneous nucleation.

The volatile content in magmas is fundamental for the triggering and style of volcanic eruptions. Carbon dioxide, the second most abundant volatile component in magmas after H2O, is the first to reach saturation upon ascent and depressurization. We investigate experimentally CO2-bubble nucleation in trachybasalt and trachyte melts at high temperature and high pressure (HT and HP) through wetting-angle measurements on different (sialic, mafic or oxide) phenocryst phases. The presence of crystals lowers the supersaturation required for CO2- bubble nucleation up to 37 per cent (heterogeneous nucleation, HeN), with a minor role of mineral chemistry. Different from H2O-rich systems, feldspar crystals are effective in reducing required supersaturation for bubble nucleation. Our data suggest that leucite, the dominant liquidus phase in ultrapotassic systems at shallow depth (i.e. <100 MPa), facilitates late-stage, extensive magma vesiculation through CO2 HeN, which may explain the shifting of CO2-rich eruptive systems towards an apparently anomalous explosive behaviour

The italian quaternary volcanism

The peninsular and insular Italy are punctuated by Quaternary volcanoes and their rocks constitute an important aliquot of the Italian Quaternary sedimentary successions. Also away from volcanoes themselves, volcanic ash layers are a common and frequent feature of the Quaternary records, which provide us with potential relevant stratigraphic and chronological markers at service of a wide array of the Quaternary science issues. In this paper, a broad representation of the Italian volcano logical community has joined to provide an updated comprehensive state of art of the Italian Quaternary volcanism. The eruptive history, style and dynamics and, in some cases, the hazard assessment of about thirty Quaternary volcanoes, from the north ernmost Mt. Amiata, in Tuscany, to the southernmost Pantelleria and Linosa, in Sicily Channel, are here reviewed in the light of the substantial improving of the methodological approaches and the overall knowledge achieved in the last decades in the vol canological field study. We hope that the present review can represent a useful and agile document summarising the knowledege on the Italian volcanism at the service of the Quaternary community operating in central Mediterranean area

Tidal modulation of eruptive activity at open-vent volcanoes: evidence from Stromboli, Italy

Terra Nova, 24, 233237, 2012 Abstract The role of Earth tides as a relevant controlling factor of a variety of geological processes, including seismicity and volcanism, is widely debated. Stromboli Volcano, Italy, is well known for its persistent explosive activity and represents an ideal setting to investigate tidal effects on the energy release and eruptive behaviour of volcanoes. Herein, we report new evidence that tidal stresses may modulate the timing of eruptive activity at volcanoes in an open-vent state. We report statistically significant correlations of the peak eruption frequencies to fortnightly tidal maxima (i.e. full and new moon) during a 17-month-long period of activity in 20102011: in fact, the number of explosive events per hour increases by >85% during tidal maxima with respect to the average values. We suggest that tidally induced cycles of compressiondecompression of country rocks controls fluctuating magma supply rate from the shallow plumbing system and, thus, eruption frequency

On the space-time distribution of major explosive volcanic eruptions on Earth

Explosive volcanic activity on Earth is typically discontinuous in space and time. The occurrence of spatial/temporal eruption clusters due to mutual cause-and-effect relationships or external triggers (e. g., tectonic and/or tidal forcing) is still debated. To detect possible clustering of major explosive eruptions, we test the distribution of eruptions with Volcanic Explosivity Index (VEI) >= 4 from 1750 to present. The 143 documented VEI >= 4 events display a markedly non-uniform frequency distribution, with the highest relative probability of eruption recurrence within 500 km distance from the preceding event. The analogous frequency pattern obtained from randomized data series of the same catalogue suggests that the observed eruption pattern is primarily imparted by the geodynamic distribution of volcanoes (mostly located along tectonically active linear belts), with no evidence of mutual or external influence. Our results highlight a counter-intuitive array of major eruption loci as a consequence of the intrinsic worldwide asymmetry of explosive volcanism, with implications on hazard assessment. Citation: Palladino, D. M., and G. Sottili (2012), On the space-time distribution ofmajor explosive volcanic eruptions on Earth, Geophys. Res. Lett., 39, L12308, doi: 10.1029/2012GL052541

Earth's spin and volcanic eruptions: Evidence for mutual cause-and-effect interactions?

The angular velocity of Earth's rotation shows decadal oscillations due to the lunisolar gravitational torque, as well as inter- or intra-annual changes arising from the angular momentum exchange between the atmosphere and the solid Earth. The energies involved in the Length of Day (LOD) variations may affect the crustal deformation rate and seismic energy release on a global scale. We found significant correlation between the occurrences of major volcanic eruptions and the LOD pattern since AD 1750. On a multiyear scale, eruption frequency worldwide increases with LOD changes. Moreover, the injection of sulphur gases into the atmosphere during major eruptions is accompanied by significant inter-annual LOD variations. This provides evidence of complex mutual cause-and-effect interactions: stress changes induced by multiyear variations in Earth's spin may affect climactic volcanic activity; also, the atmosphere's dynamic response to volcanic plumes may result in global changes of wind circulation and climate, with consequent LOD variations

Constraints on magma-wall rock thermal interaction during explosive eruptions from textural analysis of cored bombs

Cored bombs, a kind of pyroclast consisting of a lithic core surrounded by a chilled shell of juvenile material, record the thermal interaction of magma with wall rocks. We performed textural analysis of cored bombs, solid-melt heat-transfer theoretical modelling, and high-temperature coating experiments to put temporal and intensity constraints on the thermal interaction of potassic magma feeder systems with carbonate wall rocks during explosive eruptions in the Quaternary, Colli Albani Volcanic District (Roman Province). It appears that the degree of thermal alteration of lithic cores records the duration of magma-core heat transfer, whereas the core/shell size ratio records the initial entrainment temperature of the lithic fragment. Both parameters appear to vary significantly with the eruptive style, magnitude and vent location. Specifically, small-scale (similar to 0.1-1 km(3) DRE) hydromagmatic eruptions show magma-core heat-transfer durations of 0.1-10 s and entrainment temperatures in the range of 100-300 degrees C in the case of a monogenetic maar located in the Colli Albani peripheral area, while entrainment temperature is as high as to 800 degrees C for a polygenetic maar in a high-enthalpy geothermal system at the margins of the main Colli Albani magma chamber. A large-scale (similar to 30 km(3) DRE) caldera-forming explosive event shows magma-core heat-transfer duration in the order of 10(2)-10(3)s and temperature of 100-500 degrees C at the initial magma-wall rock contact. On these grounds, we derived the cooling rate of magmas as a function of the initial temperature, mass and size distribution of lithic clasts entrained. Magma cooling by lithic entrainment may have occurred on the same time-scale as that of eruptive pulses (seconds to hours), implying that lithic entrainment may effect changes in magma physico-chemical properties on a short time-scale and, consequently, affect eruptive conduit dynamics. (C) 2010 Elsevier B.V. All rights reserved