Today I was watching the 10-minute imagery from the Japanese Himawari geostationary weather satellite for the next eruption of Mt. Agung in Bali, Indonesia, and in the last hour or so there have been some distinct flashes in the nighttime imagery, which you can access here. These only show up in the nighttime imagery.
Thinking this was just sensor noise, I examined other areas for similar flashes, and saw none. But after reviewing nighttime imagery over the last week, I saw similar behavior during the early stages of the eruption on Nov. 26. The flashes appear first, and then the ash cloud appears. Since the eruption plume does not show up in nighttime imagery until it has reached a sufficient altitude to be cold enough to show up in infrared sensors, it seems the lightning is more prevalent early in the eruption (assuming that’s what this is).
So, there might be a new eruption of Agung in progress. Last I checked the news, however, I saw nothing.
I’m also surprised that lightning would show up in geostationary satellite imagery of a volcanic eruption (except in a sensor designed to measure lightning, as is now carried on GOES-16). If I am wrong, please let me know.
CLARIFICATION: I realize that volcanic eruptions can produce lighting; what I have never seen before is geostationary satellite evidence of such lightning. In fact, I haven’t even heard of thunderstorm lightning being picked up by regular weather satellites, although I could be mistaken.
UPDATE: It appears that the flashes are not lightning, but are either (1) hotspots in the 3.9 micron portion of this product, a channel which is also used to detect wildfires, or (2) some portion of the eruption cloud that has low emissivity at 3.9 microns. Evidence for the latter possibility is that if you look at the early stages of a different volcano eruption in GOES-12 imagery documented here, there is a hotspot (in this case, color-coded as dark) in the 3.9 micron imagery, but then two bright flashes appear as the eruption begins. Source