Abstract
Observations of volcanic lightning made using a lightning mapping array during the 2010 eruption of Eyjafjallajökull allow the trajectory and growth of the volcanic plume to be determined. The lightning observations are compared with predictions of an integral model of volcanic plumes that includes descriptions of the interaction with wind and the effects of moisture. We show that the trajectory predicted by the integral model closely matches the observational data and the model well describes the growth of the plume downwind of the vent. Analysis of the lightning signals reveals information on the dominant charge structure within the volcanic plume. During the Eyjafjallajökull eruption both monopole and dipole charge structures were observed in the plume. By using the integral plume model, we propose the varying charge structure is connected to the availability of condensed water and low temperatures at high altitudes in the plume, suggesting ice formation may have contributed to the generation of a dipole charge structure via thunderstorm-style ice-based charging mechanisms, though overall this charging mechanism is believed to have had only a weak influence on the production of lightning.
Highlights
Volcanic plumes transport large masses of ash and magmatic gases high into the atmosphere (Sparks et al 1997)
The very high frequency (VHF) sources show a clear trajectory towards the southeast, with lightning extending beyond 20 km from the vent (Fig. 5), suggesting the plume trajectory was strongly affected by the northwesterly winds
The discrepancies may be due to limitations of the meteorological data, in particular a difference in the wind direction obtained from the numerical weather prediction (NWP) with respect to the actual wind field leading to the apparent off-set of the modelled plume trajectory from the VHF sources, in addition to simplifications in the derivation of the model
Summary
Volcanic plumes transport large masses of ash and magmatic gases high into the atmosphere (Sparks et al 1997). Pyroclasts in volcanic plumes result from fragmentation of magma within the conduit (e.g., Wilson et al 1980; Sparks et al 1997; Woods 1998; Kaminski and Jaupart 1998) and erosion of the conduit wall (Wilson et al 1980; Macedonio et al 1994) and are transported within the plume until the vertical velocity of the gas falls below the particle settling velocity (Wilson and Walker 1987; Woods and Bursik 1991).
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