Triggering Of Volcanic Eruptions Research Articles

The influence of water in silicate melt on aluminium excess in plagioclase as a potential hygrometer

Measuring water contents of magmas is fundamental to resolving a number of geological questions, such as the mechanisms of silicic magma evolution, the triggering of volcanic eruptions, and the formation of porphyry copper deposits. This study focuses on the correlation between apparent deviations from stoichiometry of plagioclase crystals and high water concentration in the magmatic melt from which they grew. We considered this relationship as a potential geo-hygrometer (water activity indicator). To test and potentially calibrate this new technique, a range of natural and experimental plagioclase crystals were analysed, with particular care taken to identify and avoid analytical bias and artefacts. In contrast to recently published material, we found no systematic aluminium excess in plagioclase, irrespective of the water concentration of the silicate melt it crystallised from. This suggests that aluminium excess in plagioclase cannot serve as a geo-hygrometer. The high likelihood of misinterpreting analytical artefacts (due to alkali migration and imprecise standardisation) as small deviations from stoichiometry, also requires its application as a mineral exploration tool to be treated with caution.

Triggering of volcanic eruptions by large earthquakes

AbstractWhen a large earthquake occurs near an active volcano, there is often concern that volcanic eruptions may be triggered by the earthquake. In this study, recently accumulated, reliable data were analyzed to quantitatively evaluate the probability of the occurrence of new eruptions of volcanoes located near the epicenters of large earthquakes. For volcanoes located within 200 km of large earthquakes of magnitude 7.5 or greater, the eruption occurrence probability increases by approximately 50% for 5 years after the earthquake origin time. However, no significant increase in the occurrence probability of new eruptions was observed at distant volcanoes or for smaller earthquakes. The present results strongly suggest that new eruptions are likely triggered by static stress changes and/or strong ground motions caused by nearby large earthquakes. This is not similar to the previously presented evidence that volcanic earthquakes at distant volcanoes are remotely triggered by surface waves generated by large earthquakes.

Experimental mixing of hydrous magmas

Deformation experiments involving hydrous magmas of different compositions (basalt and haplotonalite) have been performed in a Paterson press at 300MPa, in the temperature range 600°C–1020°C, with water-saturated melts, during 2–4h. Prior to deformation, the two end-member magmas were annealed at either 950°C or 1000°C, yielding magmas with crystal contents in the range 31–53wt.% and 2 sets of viscosity contrasts. Under the experimental conditions investigated (i.e. moderate shear rates <10−3s−1), mixing/mingling textures appear at temperatures >950°C. In the temperature range 950–985°C, a few mixing and mingling textures occur, though both end-members essentially retain their physical integrity. It is only at, or above, 1000°C that a dramatic jump in mingling efficiency happens, corresponding to a crystal fraction of 45vol.%. Textures include entrainment of mafic crystals into the felsic magma, mafic–felsic banding, enclave formation, and diffusion-induced interface, the latter only over limited distances (<300μm) due to the short run durations. In the most strained parcels of interacting magmas, complex mixing/mingling textures were produced, similar to those observed in volcanic and plutonic rocks in arc settings. The experiments show that mixing between hydrous felsic and mafic magmas takes place at around 1000°C, a temperature which is almost 200°C lower than mixing under dry conditions. Magma mixing is commonly invoked as a trigger for volcanic eruptions; our experiments suggest that such eruptions can be driven by small (~15°C) temperature fluctuation in the reservoir. Our results also suggest that slow replenishment of a felsic reservoir by mafic inputs will likely result in stratification between end-members rather than in a homogeneous mixture.

Evaluating Complex Magma Mixing via Polytopic Vector Analysis (PVA) in the Papagayo Tuff, Northern Costa Rica: Processes that Form Continental Crust

Over the last forty years, research has revealed the importance of magma mixing as a trigger for volcanic eruptions, as well as its role in creating the diversity of magma compositions in arcs. Sensitive isotopic and microchemical techniques can reveal subtle evidence of magma mixing in igneous rocks, but more robust statistical techniques for bulk chemical data can help evaluate complex mixing relationships. Polytopic vector analysis (PVA) is a multivariate technique that can be used to evaluate suites of samples that are produced by mixing of two or more magma batches. The Papagayo Tuff of the Miocene-Pleistocene Bagaces Formation in northern Costa Rica is associated with a segment of the Central American Volcanic Arc. While this segment of the arc is located on oceanic plateau, recent (&lt;8 Ma) ignimbrites bear the chemical signatures of upper continental crust, marking the transition from oceanic to continental crust. The Papagayo Tuff contains banded pumice fragments consistent with one or more episodes of mixing/mingling to produce a single volcanic deposit. The PVA solution for the sample set is consistent with observations from bulk chemistry, microchemistry and petrographic data from the rocks. However, without PVA, the unequivocal identification of the three end-member solution would not have been possible.

Effect of heterogeneities on evaluating earthquake triggering of volcanic eruptions

Abstract. Recent researches have indicated coupling between volcanic eruptions and earthquakes. Some of them calculated static stress transfer in subsurface induced by the occurrences of earthquakes. Most of their analyses ignored the spatial heterogeneity in subsurface, or only took into account the rigidity layering in the crust. On the other hand, a smaller scale heterogeneity of around hundreds of meters has been suggested by geophysical investigations. It is difficult to reflect that kind of heterogeneity in analysis models because accurate distributions of fluctuation are not well understood in many cases. Thus, the effect of the ignorance of the smaller scale heterogeneity on evaluating the earthquake triggering of volcanic eruptions is also not well understood. In the present study, we investigate the influence of the assumption of homogeneity on evaluating earthquake triggering of volcanic eruptions using finite element simulations. The crust is treated as a stochastic media with different heterogeneous parameters (correlation length and magnitude of velocity perturbation) in our simulations. We adopt exponential and von Karman functions as spatial auto-correlation functions (ACF). In all our simulation results, the ignorance of the smaller scale heterogeneity leads to underestimation of the failure pressure around a chamber wall, which relates to dyke initiation. The magnitude of the velocity perturbation has a larger effect on the tensile failure at the chamber wall than the difference of the ACF and the correlation length. The maximum effect on the failure pressure in all our simulations is about twice larger than that in the homogeneous case. This indicates that the estimation of the earthquake triggering due to static stress transfer should take account of the heterogeneity of around hundreds of meters.

Heterogeneous bubble nucleation in highly viscous silicate melts during instantaneous decompression from high pressure

The nucleation of H 2O bubbles in magmas has been proposed as a trigger for volcanic eruptions. To determine how bubbles nucleate heterogeneously in silicate melts, experiments were carried out in which high-silica rhyolitic melts were hydrated at 800 °C and either 50 or 125 MPa, and then decompressed by 20–91 MPa at temperatures that ranged between 550 and 700 °C, and held at the lower pressures for 10–720 s before being quenched. Bubbles nucleated in number densities ( N B) that vary between 3 × 10 7 and 2 × 10 8 cm − 3 . Blocky shaped magnetite or the ends of needle-shaped hematite acted as sites for nucleation, but only if a minimum super-saturation was exceeded, which increases with increasing melt viscosity. Bubbles did not nucleate along the lengths of hematite needles nor on plagioclase. Both the beginning and ending times of the nucleation event increases with increasing melt viscosity. Using nucleation theory predictions, neither the slower nucleation rates nor the changing activation of nucleation sites can be adequately explained by the differences in temperature, water diffusivity, or viscosity. Instead, the variations in nucleation kinetics are best explained by changes in surface tension between melt and vapor, resulting from the increasing polymerization of the melt at lower temperatures and water contents. Because only ∼ 10 8 bubbles cm − 3 nucleate on magnetite in the rhyolite melt used, almost regardless of experimental conditions, results from this study may not be directly comparable to vesicle numbers in volcanic pumice of different compositions.

Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts

The nucleation of H 2O bubbles in magmas has been proposed as a trigger for volcanic eruptions. To determine how bubbles nucleate heterogeneously in silicate melts, experiments were carried out in which high-silica rhyolitic melts were hydrated at 740–800°C and 50–175 MPa, decompressed by 20–70 MPa, and held at the lower pressures for ≥10 s before being quenched. The hydration conditions were subliquidus, and all samples contain blocky magnetite + needle-shaped hematite ± plagioclase. Magnetite is abundant at 800°C and high pressures, whereas hematite becomes more abundant at lower temperatures and pressures. Bubbles nucleated in a single event in all samples, with the number density ( N T ) of bubbles varying between 2 × 10 7 and 1 × 10 9 cm −3. At low degrees of supersaturation, one to a few bubbles nucleate on faces of magnetite, but at medium to high degrees of supersaturation, multiple bubbles nucleate on single magnetite grains. On hematite, one to a few bubbles nucleated at the ends of the needle-shaped crystals at medium supersaturations, but formed along their entire lengths at high supersaturations. N T increases as water diffusivity decreases, indicating that the number of bubbles nucleated is influenced by their growth, which depletes the melt with respect to H 2O and lowers supersaturation. If volcanic eruptions are triggered by bubble formation in magmas stored in shallow-level magma chambers, then the supersaturations needed for heterogeneous nucleation suggest that only small amounts of crystallization are needed, whereas homogeneous nucleation is unlikely to trigger eruptions.

Triggering of volcanic eruptions

Although earthquakes and volcanic eruptions are each manifestations of large-scale tectonic plate and mantle motions, it is usually thought that the occurrences of these events are not directly related. There have been some studies, however, in which triggering of volcanic eruptions by earthquakes (remote from the volcano) has been proposed1,2. The 1992 Landers (southern California) earthquake caused triggered seismicity at very large distances3, including the magmatically active4 Long Valley caldera region which also experienced a significant coincident deformation transient5. Motivated by this demonstration of the ability of a distant earthquake to disturb a volcanic system, and the earlier studies of specific cases of eruption triggering, we examine here the historical record of eruptions and earthquakes to see if there are indeed significantly more eruptions immediately following large earthquakes. We find that within a day or two of large earthquakes there are many more eruptions within a range of 750 km than would otherwise be expected. Additionally, it is well known6 that volcanoes separated by hundreds of kilometres frequently erupt in unison; the characteristics of such eruption pairs are also consistent with the hypothesis that the second eruption is triggered by earthquakes associated with the first.

Triggering of volcanic eruptions by Earth tides

Triggering of volcanic eruptions by Earth tides

Correction [to “On the triggering of volcanic eruptions by Earth tides” by by F. J. Mauk and M. J. S. Johnston

Correction [to “On the triggering of volcanic eruptions by Earth tides” by by F. J. Mauk and M. J. S. Johnston

On the triggering of volcanic eruptions by Earth tides

erupted at or near the fortnightly tidal maximum is located in an area having a negative Bouguer anomaly, a large crustal thickness, and a small rate of horizontal crustal deformation. Conversely, volcanoes in areas characterized by thinner crusts and crustal deformation rates greater than 3.0 cm/yr generally erupt at or near the fortnightly tidal maximum. Solar and lunar tides produce in the earth's crust quasi-periodic stresses with amplitudes less than 10 s N/m s (10 -3 bar), a maximum rate of change of I N/m s sec (10 -5 bar/sec), and a maximum spatial gradient of 10 -s N/m s (10 -s bar/m). This is the largest short-period oscillatory stress in the earth's crust, and suggestions that it plays a role in triggering slowly accumulating tectonic stress have been frequent [Morgan et al., 1961; Knopoff , 1964; Stacey, 1964; Simpson, 1967;Shlien, 1972]. Detailed investigations, however, have been focused almost entirely on the question of triggering earthquakes by earth tides. It is now generally accepted that earthquakes and aftershock sequences occur at times uncorrelated with earth tides, although some particular aftershock sequences appear to be an exception [Ryall et al., 1968]. A second source of tectonic stress variation likely to be affected by periodic tidal stress occurs with volcanic eruptions. In contrast to the earthquake problem, where the rate. of stress accumulation and the geographic location of