Ash-plume dynamics and eruption source parameters by infrasound and thermal imagery: The 2010 Eyjafjallajökull eruption

Abstract

Keywords: ash eruptions plume height mass eruption rate infrasound a b s t r a c t During operational ash-cloud forecasting, prediction of ash concentration and total erupted mass directly depends on the determination of mass eruption rate (MER), which is typically inferred from plume height. Uncertainties for plume heights are large, especially for bent-over plumes in which the ascent dynamics are strongly affected by the surrounding wind field. Here we show how uncertainties can be reduced if MER is derived directly from geophysical observations of source dynamics. The combination of infrasound measurements and thermal camera imagery allows for the infrasonic type of source to be constrained (a dipole in this case) and for the plume exit velocity to be calculated (54-142 m/s) based on the acoustic signal recorded during the 2010 Eyjafjallajökull eruption from 4 to 21 May. Exit velocities are converted into MER using additional information on vent diameter (50 710 m) and mixture density (5.4 7 1.1 kg/m 3 ), resulting in an average $ 9 Â 10 5 kg/s MER during the considered period of the eruption. We validate our acoustic-derived MER by using independent measurements of plume heights (Icelandic Meteorological Office radar observations). Acoustically derived MER are converted into plume heights using field-based relationships and a 1D radially averaged buoyant plume theory model using a reconstructed total grain size distribution. We conclude that the use of infrasonic monitoring may lead to important understanding of the plume dynamics and allows for real-time determination of eruption source parameters. This could improve substantially the forecasting of volcano-related hazards, with important implications for civil aviation safety.

Quantifying unsteadiness and dynamics of pulsatory volcanic activity

“…In this study, we analysed about 100 minutes of thermal images from the 4 May, during the beginning of the second explosive phase, with explosions occurring with repose intervals ranging from 1 to 105 s. Thermal image analysis for this period shows that the plume was sustained by a series of thermal puffs of hot gases and ash, occurring at a mean period of around 30 s, and reaching heights up to 2 km a.s.l. (Ripepe et al, 2013).…”

“…Data acquisition uncertainty considered as the absolute error. References: (1) Hill et al (1998), (2) INGV (2012), (3) Ripepe et al (2013), (4) Sahetapy-Engel et al (2008), (5) Iguchi (2013), (6) Druitt et al (2002), (7) Ruiz et al (2005), (8) Varley et al (2006), (9) Webb et al (2014), (10) Watt et al (2007), (11) Dirksen et al (2006), (12) Valade et al (2012), (13) Ripepe et al (2008 Unfortunately, this complexity is not encompassed by current classification schemes as they are mostly based on deposit properties, e.g. tephra dispersal, grainsize and/or erupted volume, with the assumption of steady-state conditions (e.g.…”

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

“…These bursts are here referred to as "ash pulses". The pulsating behavior was also detected in the velocity profile of the plume (Bjornsson et al 2013) and in the infrasound signature of the eruption (Ripepe et al 2013) and was quantified for 4 May in terms of number of pulses, pulse velocities, and pulse heights by using a thermal camera (Ripepe et al 2013).…”

First results of the Piton de la Fournaise STRAP 2015 experiment: multidisciplinary tracking of a volcanic gas and aerosol plume

“…The Eyjafjällajökull eruption has demonstrated, in an emblematic way, the challenges of forecasting the temporal evolution of volcanic source parameters for volcanic plumes, as well as of accurately assessing the ash and gas content, composition and size distribution of the drifting mass (Kaminski et al, 2011;Bursik et al, 2012;Folch et al, 2012). One major source of uncertainty is the lack of accurate measurements of basic and essential parameters, such as plume height and mass discharge rate (Ripepe et al, 2013).…”