Wind eating away the Martian terrain

Week Four: Ninth Anniversary Fund-Raising Drive for Behind the Black

The fourth week of my annual anniversary fund-raising campaign for Behind the Black has begun.

I once again must thank the many readers and listeners who have generously donated this month. Right now there is a chance this will be the best fund-raiser ever, though only if a lot of people donate during the month's last ten days. If you want to help me continue my reporting, you can give a one-time contribution, from $5 to $100, or a regular subscription for as little as $2 per month.

For one time donations via Paypal, click here:

To pick a subscription option via Paypal, click here:


If Paypal doesn't work for you, you can still support Behind The Black by sending your donation by check, payable to Robert Zimmerman, to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

Yardangs on Mars

Cool image time! The Mars Reconnaissance Orbiter (MRO) image on the right, cropped and reduced in resolution to post here, shows the transition zone between the lower flat plain to the north and the higher but rougher region to the south. What makes it interesting is the north-south aligned mesas. These are yardangs, a geological feature that actually acts like a weather vane.

Yardangs are composed of sand grains that have clumped together and have become more resistant to erosion than their surrounding materials.

As the winds of Mars blow and erode away at the landscape, the more cohesive rock is left behind as a standing feature. (This Context Camera image shows several examples of yardangs that overlie the darker iron-rich material that makes up the lava plains in the southern portion of Elysium Planitia.) Resistant as they may be, the yardangs are not permanent, and will eventually be eroded away by the persistence of the Martian winds.

For scientists observing the Red Planet, yardangs serve as a useful indicator of regional prevailing wind direction. The sandy structures are slowly eroded down and carved into elongated shapes that point in the downwind direction, like giant weathervanes. In this instance, the yardangs are all aligned, pointing towards north-northwest. This shows that the winds in this area generally gust in that direction.

Crater splash

The wind comes from the southeast and blows to the northwest, and is slowly wearing down the southern rougher terrain. Why some of these yardangs are surrounded by dark material remains a mystery, as noted I noted in a previous post.

Meanwhile, the northern plain is not as boring as it seems. Only a short distance to the north is an unusual crater, cropped from the full image to show here on the right. To my eye, when this impact occurred it literally caused a splashlike feature of compressed and more resistant material. Over time, the prevailing wind has eroded away the surrounding less resistant regolith to better reveal that splash, leaving behind a mesa with a crater in its center.

Why the impact created this splash tells us something about the density and make-up of the plain. It suggests to me a surface that was once muddy and soft that over time has hardened like sandstone.


Leave a Reply

Your email address will not be published. Required fields are marked *