High‐speed imaging of Strombolian explosions: The ejection velocity of pyroclasts

Abstract

[1] Explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the Earth's crust. Knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption, and yet direct measurements are still a difficult task with largely variable results. Here we apply pioneering high-speed imaging to measure the ejection velocity of pyroclasts from Strombolian explosive eruptions with an unparalleled temporal resolution. Measured supersonic velocities, up to 405 m/s, are twice higher than previously reported for such eruptions. Individual Strombolian explosions include multiple, sub-second-lasting ejection pulses characterized by an exponential decay of velocity. When fitted with an empirical model from shock-tube experiments literature, this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses. These results directly impact eruption modeling and related hazard assessment, as well as the interpretation of geophysical signals from monitoring networks. Citation: Taddeucci, J

Recycled ejecta modulating Strombolian explosions

“…An individual Bexplosion^is characterized by multiple, second-long Bpulses^and sub-second-long Bsubpulses^, each pulse being characterized by the ejection of particles at similar velocities which then decrease in time (Taddeucci et al 2012a;Gaudin et al 2014;Bombrun et al 2015). In addition we can observe multiple emission points during a single event.…”

Application of the Monopole Source to Quantify Explosive Flux during Vulcanian Explosions at Sakurajima Volcano (Japan)

“…Taddeucci et al (2012) identify supersonic emissions for small sized Stromboli (Italy) explosions, which cause the atmosphere to respond with shock wave generation. At Sakurajima shock waves are commonly seen in video records in conjunction with the largest of the recorded infrasound transients (Akihiko Yokoo, Aso Volcanological Laboratory, personal comm., 2013).…”

From magma ascent to ash generation: investigating volcanic conduit processes by integrating experiments, numerical modeling, and observations

“…Multi-parametric monitoring of charge distribution and frequency of electrical discharges in plumes during explosive eruptions [Cimarelli et al, 2016] are starting to systematically address the links between the in-conduit explosive dynamics and the electrification of volcanic ash with the goal of constraining mass eruption rates and plume evolution in space and time. In addition, the new instruments and technologies mentioned above allow measurement of ejection velocities at higher spatial and temporal resolutions, as well as the degree of decoupling of solids and gas phases in jets [e.g., Taddeucci et al 2012, Scharff et al 2014, Taddeucci et al 2015 and, recently, the effect of particle volume fraction on the ash settling velocities [Del Bello et al 2017]. Finally, participants highlighted the importance of distinguishing between plume and conduit dynamics, especially concerning how much can be inferred regarding the latter from observations of the former.…”