Mass eruption rates in pulsating eruptions estimated from video analysis of the gas thrust-buoyancy transition—a case study of the 2010 eruption of Eyjafjallajökull, Iceland

Abstract

The 2010 eruption of Eyjafjallajökull volcano was characterized by pulsating activity. Discrete ash bursts merged at higher altitude and formed a sustained quasi-continuous eruption column. High-resolution near-field videos were recorded on 8-10 May, during the second explosive phase of the eruption, and supplemented by contemporary aerial observations. In the observed period, pulses occurred at intervals of 0.8 to 23.4 s (average, 4.2 s). On the basis of video analysis, the pulse volume and the velocity of the reversely buoyant jets that initiated each pulse were determined. The expansion history of jets was tracked until the pulses reached the height of transition from a negatively buoyant jet to a convective buoyant plume about 100 m above the vent. Based on the assumption that the density of the gas-solid mixture making up the pulse approximates that of the surrounding air at the level of transition from the jet to the plume, a mass flux ranging between 2.2 and 3.5 · 10 4 kg/s was calculated. This mass eruption rate is in good agreement with results obtained with simple models relating plume height with mass discharge at the vent. Our findings indicate that near-field measurements of eruption source parameters in a pulsating eruption may prove to be an effective monitoring tool. A comparison of the observed pulses with those generated in calibrated large-scale experiments reveals very similar characteristics and suggests that the analysis of near-field sensors could in the future help to constrain the triggering mechanism of explosive eruptions.

Investigating Source Conditions and Controlling Parameters of Explosive Eruptions: Some Experimental-Observational- Modelling Case Studies

“…However, the ash pulses within the footage taken 4, 5 and 6 days later showed an increase in the average initial vertical velocities to 65 m s −1 and-even more prominent-a significant drop of the average pulsation interval t pulse to 4.2 s, coinciding with the significantly increased overall mass flux [13]. Furthermore, these video analyses revealed that two types of explosive pulses could be discriminated by their observed diameter at the vent exit: 'strong' pulses, featuring diameter at a vent of greater than 50 m and 'weaker' pulses, characterised by a diameter at the vent exit of less than 50 m [13]. The two types also significantly differed in their rate of occurrence: the time between weaker pulses (t pulse ) was on average 4.7 s and between strong pulses on average of 37.5 s [13].…”

“…Measurements made by a thermal camera mounted at a distance of 8.3 km from the vent on 4th May revealed average initial pulse velocities of 45 m s −1 and average pulsation intervals t pulse of ∼20 s (see Table 1 for Notation), meaning that on average three pulses occurred every minute [17]. However, the ash pulses within the footage taken 4, 5 and 6 days later showed an increase in the average initial vertical velocities to 65 m s −1 and-even more prominent-a significant drop of the average pulsation interval t pulse to 4.2 s, coinciding with the significantly increased overall mass flux [13]. Furthermore, these video analyses revealed that two types of explosive pulses could be discriminated by their observed diameter at the vent exit: 'strong' pulses, featuring diameter at a vent of greater than 50 m and 'weaker' pulses, characterised by a diameter at the vent exit of less than 50 m [13].…”

“…Furthermore, these video analyses revealed that two types of explosive pulses could be discriminated by their observed diameter at the vent exit: 'strong' pulses, featuring diameter at a vent of greater than 50 m and 'weaker' pulses, characterised by a diameter at the vent exit of less than 50 m [13]. The two types also significantly differed in their rate of occurrence: the time between weaker pulses (t pulse ) was on average 4.7 s and between strong pulses on average of 37.5 s [13]. Studies of ejecta trajectories enabled characterization of the vent as a funnel with a depth of 51±7 m, an inner diameter of 8-15 m and an outer diameter (8-10 May) of 65±2 m [14].…”

“…Based on these findings, a pulse velocity-derived model (PVDM) was developed [13]. This model determines the mass flux contribution of individual ash pulses analysed in the videos in order to estimate the overall MER.…”

“…Here we use the recent innovations of Dürig et al [13,14] to highlight ways in which emerging techniques can be used to better understand source processes. Dürig et al [13,14] established a means of quantifying the mass eruption rate of individual explosive pulses at the vent based on highresolution imagery (optical and thermal) of the Eyjafjallajökull eruption. Their technique can be applied in near real-time to monitor the changing mass eruption rate.…”