Abstract During explosive eruption of low viscosity magmas, pyroclasts are cooled predominantly by forced convection. Depending on the cooling efficiency relative to other timescales, a spectrum of deposits can be formed. Deposition of hot clasts, above their glass transition temperature, can form spatter mounds, ramparts and clastogenic lava flows. Clasts may also be deposited cold, producing tephra cones and blankets. Thus, the deposit and pyroclast type can provide information about eruption dynamics and magma properties. Here we examine pyroclasts from Tseax volcano, British Columbia, Canada. These newly identified inflated pyroclasts, are fluidal in form, have undergone post-depositional expansion, and are found juxtaposed with scoria. Detailed field, chemical and textural observations, coupled with high temperature rheometry and thermal modelling, reveal that abrupt transitions in eruptive behaviour — from lava fountaining to low-energy bubble bursts — created these pyroclastic deposits. These findings should help identify transitions in eruptive behaviour at other mafic volcanoes worldwide. 

/pdf/inflated-pyroclasts-in-proximal-fallout-deposits-reveal-5ozt9l6r.pdf

Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour

The Bubble's Wake: Localized Rebound of Kīlauea's Summit Lava Lake Following Minor Bubble Bursts

The explosive activity of the 2021 Tajogaite eruption eludes pigeonholing into well-defined eruption styles, with a variety of pyroclast ejection modes occurring both alternately and simultaneously at multiple vents. Visually, we defined four endmembers of explosive activity, referred to as fountaining, spattering, ash-poor jets and ash-rich jets. To capture the physical parameters of these activities, we deployed a camera array including one high-speed camera and three high-definition cameras in two field campaigns. Transitions between and fluctuations within activity occurred at the time scale of minutes to hours, likely driven by the same shallow conduit and vent processes controlling Strombolian activity at other volcanoes, but at higher gas and magma fluxes. From a physical standpoint, mean pyroclast rise velocity ranged 5–50 m/s, maximum ejection velocity 10–220 m/s, and sub-second mass flux of lapilli to bomb-sized pyroclasts at the vent 0.2–200 × 103 kg/s. The largest mass flux occurred during fountaining, which contributed by far more than other activities to cone building. All explosive activity exhibited well-defined pyroclast ejection pulses, and we found a positive correlation between the occurrence rate of ejection pulses and maximum pyroclast ejection velocity. Despite orders of magnitude variations, physical parameters shift gradually with no boundary from one activity endmember to another. As such, attributing this explosive activity specifically to any currently defined style variations is arbitrary and potentially misleading. The highly variable explosive activity of the Tajogaite eruption recalls previous definitions of violent Strombolian eruptions, an eruption style whose pyroclast ejection dynamics, however, were so far largely undefined. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2023GC010946

The Explosive Activity of the 2021 Tajogaite Eruption (La Palma, Canary Islands, Spain)

Abstract The Hadamard–Rybczynski equation describes the steady‐state buoyant rise velocity of an unconfined spherical bubble in a viscous liquid. This solution has been experimentally validated for the case where the liquid viscosity is held constant. Here, we extend this result for non‐isothermal conditions, by developing a solution for bubble position in which we account for the time‐dependent liquid viscosity, liquid and gas densities, and bubble radius. We validate this solution using experiments in which spherical bubbles are created in a molten silicate liquid by cutting gas cavities into glass sheets, which are stacked, then heated through the glass transition interval. The bubble‐bearing liquid, which has a strongly temperature‐dependent viscosity, is subjected to various heating and cooling programs such that the bubble rise velocity varies through the experiment. We find that our predictions match the final observed position of the bubble measured in blocks of cooled glass to within the experimental uncertainty, even after the application of a complex temperature–time pathway. We explore applications of this solution for industrial, artistic, and natural volcanological applied problems.

Bubble rise in molten glasses and silicate melts during heating and cooling cycles

Basaltic volcanism is the dominant mode of volcanism on Earth and exhibits a range of activity, from passive degassing to the most common explosive style: strombolian volcanism. Strombolian volcanism is driven by gas slugs, making it vital to consider the effects of variable magmatic rheology and internal vent geometry on slug flow dynamics. Emerging experimental technologies play a major role in developing our understanding of the natural complexity of such basaltic systems. This study examines slug ascent within particle-free and particle-containing media experimentally across a range of inclinations. Dimensionless parameters are derived to describe specific flow characteristics at laboratory and volcanic scales, and to demonstrate the viability of current theoretical framework. Slug ascent is shown to be dependent on its morphology, which is a function of inclination, liquid viscosity, and related controlling characteristics i.e. particle fraction. Maxima for ascent velocities and associated dimensionless parameters occur within the range 40—60°.

Crystals and inclined conduits: analogue experiments for slug-driven volcanism

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/pdf/patterns-of-bubble-bursting-and-weak-explosive-activity-in-428eq3tp05.pdf

Bianca G. Mintz

Papers

Patterns of bubble bursting and weak explosive activity in an active lava lake—Halema‘uma‘u, Kīlauea, 2015