Last week, I reported that Karkar in Papua New Guinea had erupted. This was based on reports from Volcano Live and from the Darwin VAAC that said the volcano had produced at least 1, maybe 2, ~13 km / 45,000 foot ash columns. That is not a trivial ash column - you would think a large eruption was needed to produce such an ash column (and you'd be right).
Then, no news. Nothing. I (and other Eruptions readers) scoured the web for more information on this phantom eruption at Karkar. Not a peep on noise about any eruption, let alone an eruption to send ash above 40,000 feet.
Recent reports from the ground from Jan Messersmith, living in Madang, near Karkar had this to say:11/26/2009:
I live in Madang. We felt a minor earthquake at the time mentioned. However, though obscured by some clouds, we looked in vain for any action at Kar Kar Island, which I can see clearly from my veranda. We called friends who live on Kar Kar island and they told us that nothing was happening. Tomorrow (Saturday 28 November) I'm going to go over there in my boat to see if I can get some pictures, if anything is going on. Nobody in Madang has seen any activity. Could there be some error? We watch Kar Kar pretty carefully. I can't imagine that we could miss any action this significant.Then, yesterday, 11/28/2009:
It's now Sunday morning here in Madang. I was out on the boat for several hours yesteday with Kar Kar in plain view about 50 kilometres away. We saw nothing out of the ordinary. We have seen minor eruptions before, with some ash and gas. There was nothing of this nature yesterday or any other day since the report. Nobody around here has heard any reports of activity. There are boats going back and forth every day and we have phone contact with friends on the island who have reported no activity. This looks pretty much like an incorrect report. Either that or it is the virst major invisible eruption.
This would all suggest that, in fact, no eruption happened at Karkar (and the Volcanism Blog would concur with this conclusion). So, what happened? Readers have suggested that maybe a large thunderhead in the region of Karkar "tricked" the satellite monitoring software at the VAAC to think Karkar had erupted. It was cloudy and stormy in the region at the time that the eruption was reported. Any other ideas what might produce this large "false positive" for an eruption? This goes to show that monitoring volcanoes using remote sensing such as satellite imagery has its definite limitations - we can at least hope that it errs on the side of caution. I don't know about you, but I'd much rather have it "see" an eruption that didn't happen than vice versa.