Look out below!
HiRISE caught an avalanche in action! http://hirise.lpl.arizona.edu/PSP_007338_2640
It was so exciting to find this image! The image was intended to be part of a series of seasonal monitoring observations of a dune field. We’re watching to see how the winter carbon dioxide frost disappears as spring comes to the northern polar areas (which is pretty cool in itself! See PSP_007043_2650, for example.) PSP_007338_2640 happened to be the first image we took after powering back on after a safing event. So we were examining the image to make sure the camera was still working OK (it is – as you can see from this beautiful image & the many others we’ve taken since!). If it hadn’t been for that, we might not have noticed this for weeks! (In case you haven’t noticed, we have a LOT of images to look at! 
)
My first reaction was just, “What is that?” So I asked some of the scientists around HiROC, and they got excited, too. Everyone was talking about it all day, putting together ad-hoc color products (the full color processing takes a while to get through our processing pipelines) and looking at other images nearby for similar events. Because this was part of a series of images in the same spot, we had a “before” image as well (PSP_007140_2640). It’s a little hard to compare the two images because the bright carbon dioxide frost is changing as well, and we took the two images from different angles. But you can see in the second image that there are some spots up above on the cliff that are missing their bright frost covering. Perhaps that’s where the rock (or ice) fall started? The springtime sun is warming these icy layers, which could cause sublimation (solid ice changing to gas). Certainly there is a lot of dust being raised to form this big cloud, too, whether the dust was mixed in with the ice blocks, or just kicked up off the lower, dustier layers. As we continue monitoring this site and other polar areas, we’re sure to learn a lot more about the processes captured in this image.
ETA: Emily Lakdawalla made a great animation of the before/after shots, posted on the Planetary Society blog. So cool! 
March 4th, 2008 at 2:26 pm
[...] we are a Before & During landslide. Andrew Brown. __________________ "Youngerford, let me see, you were asleep in [...]
March 4th, 2008 at 3:24 pm
Great observation. Seeing a change like this in REAL TIME is just incredible, plus a good view of the same feature pre landslide. Hopefully we get to see the same location again in the near future, do see what scal of change & possible cause.
Andrew Brown.
March 4th, 2008 at 8:32 pm
[...] {Also: The first sighting of a Martian avalanche. Luckily, no Martian actually died. However.} [...]
March 4th, 2008 at 10:23 pm
Now that you have TWO images of this area would it be possible to RELEASE to the PUBLIC a 3D USGS DEM for importation into a destop 3D program like Bryce 5?
March 5th, 2008 at 7:01 am
[...] snow, and the fall of snow or ice has kicked up dust over on the right. They’ve even found a before and after image. Like I said, stunning – and think what must be in the other 16.8 TB (yes, TeraBytes) of data that [...]
March 5th, 2008 at 5:55 pm
I think I found an earlier avalanche in the “before”-image taken Feb.3.2008 (PSP_007140_2640).
Link to comparison images: http://img88.imageshack.us/img88/9439/uusivyoryhv3.png
Maybe these happen frequently in the springtime??
/speculation
March 9th, 2008 at 4:33 pm
Very interesting to see it live as it happens. HiRise may have caught another in the act last year. An image monitoring the Russell Crater dunes and their assiciated “gullies” shows several clouds of dust at the lower end of at least two “gullies.” The image in question is PSP_002904_1255 acquired on March 10, 2007. They are not as clear as the polar examples but still they look pretty interesting.
March 11th, 2008 at 7:47 am
Are these necessarily avalanches, or could we instead be seeing sublimated CO2 gas flowing down the cliff and kicking up dust at the bottom, like a waterfall? The evidence against this idea is that if it were so, one would expect to see the effect along the entire length of the bluff, all other things (solar exposure, e.g.) being equal.
March 12th, 2008 at 8:56 am
[...] seems the landslides in PSP_007338_2640 have caught a lot of [...]
August 7th, 2009 at 8:52 pm
While the landslides are interesting, I find the geyser like feature at pixel 120353,30593 to be even more interesting…