The mystery glow on Mount St Helens
UPDATED 13 September 2005
On the night of the 3rd of May 2005 a new hotspot appeared on the Volcanocam images on the western flank of the crater. Unlike the glow from the lavadome that has been visible since 11 October 2004, this appeared to be a much smaller and more defined source. Adding to the mystery of what it could be was its location - outside of the crater rim and far removed from the extruding lava and the growing lavadome.
The anomalous glow was bright, but varied in intensity throughout the night, as seen in these movies of the night time images (Macromedia Flash format):
Night of 03/04 May - animation showing the
enhanced images of the glows superimposed on a background image of the mountain. (size 498 kB)
Night of 03/04 May - animation showing just the glows. (size 454 kB)
The anomalous glow reappeared the next night 04/05 May (size 173 kB) and then intermittently on the nights of 11/12 May (size 244 kB), 12/13 May (size 203 kB) and 14/15 May (size 365 kB). It wasn't visible at all in the most recent images from 15-21 May. But reappeared with the clear weather on the night of 25th May (size 382 kB) and appear even brighter on subsequent nights (see for example 27/28 May).
Many possible explanations have been suggested as to what this may have been, including: a defective (hot) pixel in the CCD camera; a campfire; a new volcanic vent; overheating scientific/monitoring equipment; car headlights reflecting off equipment; a reflection off of the cowling or case protecting the camera; and cosmic rays striking the CCD.
Most of these explanations were quickly eliminated. The USGS quickly confirmed that there was no sign of new volcanic activity in the region where the glow was located and that they didn't have any equipment in the general area. The idea that it could have been the result of illegal climbers lighting a bonfire was also looking unlikely due to the size of the fire that would have been required to give this response on the Volcanocam images and the fact that the glow was visible over a span of more than a week (and has since reappeared again).
A cosmic ray striking the CCD would produce a brief flash, but wouldn't persist for days and vary in intensity as we see in the images. Similarly car headlights reflecting off of a piece of equipment on the mountain seems highly unlikely as the area around the mountain is closed to the public at nights (and the mountain wasn't open to the public when the glow first appeared).
The possibility of a hot (defective) pixel in the CCD camera seemed to be the most popular explanation. However, this didn't seem to fit with the behaviour observed in the images. Examining a highly magnified view of the anomalous glow over the first two nights of images, we can see that it is not just one hot pixel, but varies in size and intensity over time. Also, as the glow appeared on some nights, but then not at all on other nights, it seemed to suggest that the source may have been a real source on the mountain.
However, on 12th September 2005 the lens of the Volcanocam camera was cleaned and during the process it was moved slightly from its previous position. This provided the ideal opportunity to determine if the glow was indeed a real source on the mountain or a defective pixel. Comparing the images from the nights of the 11 & 12th of September clearly shows that the position of the hotspots do not change, even though the view of the crater does. So the only conclusion to draw is that the mystery glow is nothing more than defective pixels on the camera. (Actually there are two hotspots that are apparent in the images, the second is to the left of the centre of the images).
But the question still remains, why did the hotspot on the crater appear on some nights and not others, and more intriguingly, why did it appear to vary in size and brightness? I think this is probably due to the way the Volcanocam images are recorded and processed before transmission to the US Forest Service webserver. The Volcanocam consists of a Sanyo, Model #VCC-4594 Color CCD camera, with an analogue NTSC video signal output - this is not a direct digital image from the CCD. The signal is fed to a computer where it is re-digitised and resized before being transmitted to the Volcanocam webserver. I suspect that it is during this conversion of the original digital data from the CCD to analogue video, then being further processed back to the digital domain (and any other processing/resizing) that adds the apparent variability to the hot pixels in the final images. At least that's my best guess at the moment...