Relating vesicle shapes in pyroclasts to eruption styles

Abstract

Vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions. Although their numbers and sizes are used routinely to infer aspects of eruption dynamics, vesicle shape remains an underutilized parameter. We have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles, using the dimensionless shape factor , a measure of the degree of complexity of the bounding surface of an object. For each of the seven eruptions, we have also estimated the capillary number, Ca, from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling. We find that is smaller for eruptions with Ca 1 than for eruptions with Ca 1. Consistent with previous studies, we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth, such as coalescence and shape relaxation of bubbles by capillary stresses. Among the samples analyzed, Strombolian and Hawaiian fire-fountain eruptions have Ca 1, in contrast to Vulcanian, Plinian, and ultraplinian eruptions. Interestingly, the basaltic Plinian eruptions of Tarawera volcano, New Zealand in 1886 and Mt. Etna, Italy in 122 BC, for which the cause of intense explosive activity has

On the interaction between shear dusty currents and buildings in vertical collapse: Theoretical aspects, experimental observations, and 3D numerical simulation

“…Surprisingly, these values of energy are similar to those obtained in physical volcanology with experiments on stress-induced brittle fragmentation for natural silicate melts (Büttner et al 2002(Büttner et al , 2006. This type of fragmentation occurred in the WTC collapse, in which a fragmentation front propagated floorby-floor with negligible capillary forces (gravity dominated), and in equilibrium with the surrounding atmospheric pressure, which is evident from the videos of such vertical collapse (see also Moitra et al 2013). Literature on the pulverization of brittle materials like concrete (Hughes 1972; Bischoff and Perry 1995; see also Gudmundsson 2011), or more generally of materials behaving as brittle within stress limits (e.g.…”

Conduit Dynamics in Transitional Rhyolitic Activity Recorded by Tuffisite Vein Textures from the 2008–2009 Chaitén Eruption

“…By contrast, banded and dense clasts have more diverse, angular forms, with some clast margins bearing fractures associated with initial clast formation. Vesicle shapes are mostly near-circular, with coalescence creating some less regular forms ( Figure 3D; Moitra et al, 2013). Coalescence has largely failed to create pervasive connected channels or open porosity because of enclosure by dense clast margins.…”

“…Shape factors such as regularity, elongation and eccentricity provide useful comparison of clast and vesicle forms (Shea et al, 2010;Moitra et al, 2013), and reveal that vesicular clasts are more rounded than dense clasts (for the main vein: average regularity 0.94 vs. 0.90, elongation 0.27 vs. 0.31, eccentricity 0.78 vs. 0.81). This reflects clast inflation by vesiculation, despite local embayments forming through impingement by denser neighboring clasts ( Figure 3D).…”

Quantifying unsteadiness and dynamics of pulsatory volcanic activity

“…MacDonald, 1972;Walker, 1973;Pyle, 1989). Pulsatory volcanic activity has been also studied in terms of fluid and source dynamics at specific volcanoes (Mason et al, 2006;Sahetapy-Engel et al, 2008;Marchetti et al, 2009;Gonnermann and Manga, 2012;Moitra et al, 2013). In the context of these studies, it is important to quantify unsteadiness and relate it to traditional eruptive styles.…”