Interpreting satellite imagery

Sometimes when you see satellite imagery you can be utterly blown away by what you see.  In many of these cases there is no question about what you are looking at.

The NASA Earth Observatory has posted a number of images of Kizimen volcano in Russia since the onset of its current eruptive phase in December, including this spectacular image showing the volcano, an eruptive plume, and recent lava flows.

This afternoon, however,  Rob Simmon, a Data Visualiser at the NASA Earth Observatory posted up a picture taken yesterday by EO-1‘s Advanced Land Imaging instrument in which the image interpretation was not so straightforward.

The question is what is that thing labelled as a block and ash flow in the middle of the image?

The main vent of the volcano sits just off to the left of the frame, with the eruption plume being carried by the wind to the East. The dark brown lobes are lava flows, and the highlighted area appears to show a steam or ash plume.  Below is a slightly enlarged version.

It is not what I would typically associate with a pyroclastic flow. If you look at the enlarged image it appears that there is a point source – or at least a narrow linear source running North-South, which is then being deflected South East by the wind.  The northern portion of the plume is really very narrow (10’s of meters).  Erik Klemetti of Eruptions suggested it might be fumarolic activity, which I think is certainly a possibility.

Looking at it more closely again now, it appears there may even be two point sources – one at the northern end, and possibly a second just SE of the end of the line labelled “block & ash flow?”

If it is a pyroclastic flow, then it’s a very small one (actually not dissimilar to the type I wrote about yesterday) – probably more of a block-and-ash flow than a sustained fluidised PDC. The greyness of the area suggests it may be a deposited flow, in which case this plume may represent outgassing from a flow deposit rather than a co-ignimbrite plume (a large turbulent cloud of fine ash which forms above a pyroclastic flow, often getting separated from it by the wind). However, it’s strange that there is no clear flow path which might indicate the route any PDC might have taken.  I would certainly have expected it to leave some kind of signature on top of the lava fields if it passed that way.

I’ll update if we ever get to the bottom of it. Any other ideas gratefully received.


Rob sent me this image, which is the same frame but false colour, highlighting the shortwave IR spectrum.  It clearly shows a hot region at the foot of the northern lava flow.

The following image is a composite I have compiled which overlays the IR data onto the image from yesterday.

This suggests that the secondary plume is probably not related to pyroclastic flow, as this would be expected to also show high temperature. (See Rob’s comment below. We still haven’t eliminated the possibility).  The high IR emission appears to be solely associated with the northern lava lobe.

All images copyright and courtesy of the NASA Earth Observatory.

Finally, a Google Earth shot of Kizimen, looking North to give an idea of topography.

About Pete Rowley

Earth Scientist with a background in volcanology and sedimentology. Enjoys a good rant, beer, and games. Dislikes reality TV, crowds, and unreasonable people.
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4 Responses to Interpreting satellite imagery

  1. Pete: Keep in mind that this is shortwave infrared (2.1 micrometers), not thermal infrared, so the suface needs to be blistering hot to show up as red (especially anything that’s less than 30 meters square in area, which is the resolution of the color & IR bands (we sharpened the natural-color image with a 10 meter per pixel panchromatic band)).

    I’ll keep checking new imagery to see if the feature is persistent, but fumaroles seem unlikely to me. This is way down at the foot of the mountain. Could it be steam from melting/vaporizing snow escaping through a block and ash flow that’s a few hours old?

  2. Pete Rowley says:

    It could be steam, yes. My concern about the PDC outgassing diagnosis is that there really does seem to be a point-source nature to that plume. I look forward to finding out if there’s any persistence to it.

    As far as the temperature goes, yes – excellent point. However, for a PDC that close to the vent we should be talking about temperatures of around 300+ degrees C I would guess. Would that be enough to show up in shortwave IR?

  3. Yeah, maybe there’s a point source, but it also looks like there’s a fan of darker material that underlies the entire plume. I’m not sure if 300 degrees C would show up, if it’s big enough, probably, but I’m not sure how much contrast there would be.

    My only other guess is a large, hot boulder rolled off the lava flow, then hit some sort of obstruction and exploded. (But now I’m just speculating wildly.)

    On the other hand, take a look at this ASTER image from January 11:

    This is slightly lower-res, but you can see a dark spot on the snow in the same location, so it does look like there’s material regularly falling off the end of the lava flow (which could easily be over 100 meters tall) and southeast past the pointy ridge. I think these slopes are very, very steep, an effect that gets lost in the satellite imagery, which is taken nearly perpendicular to the Earth’s surface. Also note the fumarole to the northeast of the summit.

    • Pete Rowley says:

      It would have to be a hell of a lot of material spalling off the front of the flow though.

      They’re certainly steep slopes.

      There’s a steam cloud in that Aster image coming from the same area (although at a different point). I’m wondering if that southern lava lobe has a very small volume of lava actively flowing. That steam would represent the point at which it met the snow.

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