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A cliff face of volcanic erosion on Mars

A cliff face of volcanic erosion on Mars
Click for full image.

Today’s cool image is a variation of yesterday’s, showing another area on the edge of Mars’ largest volcanic ash field, dubbed the Medusae Fossae Formation and about the size of India. This time however the edge is an abrupt cliff, not the slow petering out of wind-shaped mesas.

The picture to the right, cropped, reduced, and sharpened to post here, was taken on August 27, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what I very roughly estimate to be a 1,500 to 2,500 foot high cliff that appears to delineate the edge. To the north we have a plateau of intersperse layers of flood lava and ash. To the south those layers have eroded away, leaving a rough lava plain with a handful of scattered wind-sculpted mesas.

The overview map below, by providing a wider view of his region, makes its nature clearer.

Overview map

The white cross marks the location of today’s photo. The inset provides a more detailed view of this region. As with yesterday’s cool image, this photo shows a spot near the northern edge of the Medusae Fossae Formation. Here however the ash field is eroding away not like a dune field but in chunks, producing distinct but randomly distributed canyons. Based on the shape of the few mesas, the prevailing wind here appears to come from the southeast.

The central geological question is this: Why did the erosion in this part of the Medusae ash field produce such an abrupt cliff, and not a more gradual change as in yesterday’s image? The canyons and cliffs suggest a faster and more violent cause for the erosion, which further suggests that while wind played the dominant role in yesterday’s picture, in today’s image we could be seeing evidence of either glacial or liquid erosion.

As always, I am as an uneducated tourist merely guessing. The cause in the difference could also simply be a difference in the nature of the ash and lava. Yesterday’s ash could be more like sandstone, and thus break up more easily by the wind. Today’s ash might be stronger structurally, with solid layers of lava holding it together. Thus, wind still does the job, but it only erodes the ash when a large piece breaks off, rather then when tiny sand particles are blown away.

Conscious Choice cover

Now available in hardback and paperback as well as ebook!


From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


All editions are available at Amazon, Barnes & Noble, and all book vendors, with the ebook priced at $5.99 before discount. The ebook can also be purchased direct from my ebook publisher, ebookit, in which case you don't support the big tech companies and I get a bigger cut much sooner.


Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95; Shipping cost for either: $5.00). Just email me at zimmerman @ nasw dot org.

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