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.