Cool image time! The two images to the right, both cropped to post here, were taken six years apart by Mars Reconnaissance Orbiter (MRO) of the western lava slopes of the giant volcano Olympus Mons. They show the appearance of a dark dust avalanche during the interim. As noted by members of the MRO science team.
Dust avalanches create slope streaks that expose darker materials usually hidden below a lighter-toned layer. Cascading fine-grained material easily diverts around boulders or alters direction when encountering a change in slope. The dark steak … is approximately 1 kilometer in length that we didn’t see in a previous image. Past avalanche sites are still visible and fading slowly as dust settles out of the atmosphere and is deposited on the dark streaks over time.
We also see boulders and their shadows that are a meter or greater in size. Movement of any of these boulders down the slope could trigger future avalanches.
The appearance of these Martian dark streaks on slopes is actually not uncommon. As more pictures are taken of Mars scientists are beginning to accumulate a large number all across the Martian surface.
What I find fascinating is the wet look of these dark streaks. Below is a close-up of the new avalanche, near its head.
The avalanche itself is not wet, but in many ways it acts like it is. Underground ice might be involved in initiating events, but it is not water that is flowing downhill but dirt and dust. The theory is that the avalanche disturbs surface material, darkening it. Over time the darkening fades, as indicated by the other fading avalanches nearby. The close-up to the right, cropped to post here, shows this. Where large boulders blocked the flow downhill, the ground remained lighter.
While avalanches on Mars will function much like they do on Earth, the lighter gravity as well as the alien environment, will change things. These dark avalanches give us a hint of those differences.
Please consider donating to Behind the Black, by giving either a one-time contribution or a regular subscription, as outlined in the tip jar below. Your support will allow me to continue covering science and culture as I have for the past twenty years, independent and free from any outside influence.
Regular readers can support Behind The Black with a contribution via paypal:
If Paypal doesn't work for you, you can support Behind The Black directly by sending your donation by check, payable to Robert Zimmerman, to
Behind The Black
c/o Robert Zimmerman
Cortaro, AZ 85652