Bottom edge of Martian glacier?


Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

 
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit.

 
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"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs." --San Antonio Express-News

The foot of an inactive glacier on Mars
Click for full image.

Today’s cool image, taken on May 25, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), provides a nice example of the typical foot of an inactive buried glacial flow on Mars. The image to the right, rotated, cropped, and reduced to post here, focuses on the center of the full image. Uphill is to the right. The glacier’s edge runs down the middle left of the photo.

Scientists call this a lobate flow because its shape resembles a lobe, smooth and rounded as it comes down the slope. Located at 38 degrees south latitude to the east of Hellas Basin and just to the north of one of that basin’s major infeeding canyons, Harmakhis Valles, this flow comes down the west side of a large mountain. The overview map below provides the context, with the white rectangle indicating the photo’s location.

Overview map

Close-up of the glacier's bottom edge

The glacier here is not considered active. As planetary scientist Alfred McEwen of the Lunar & Planetary Laboratory in Arizona explained to me in a previous post about glaciers just to the south and east of this image,

These are remnant glaciers. Basically they form like glaciers form. They are not active or if they are they are moving so extremely slowly that effectively they are not active.

And as with the glaciers in that earlier post, the repeating lines in this lobate flow (as shown in the close-up of one section of the above image at full resolution to the right) suggest many repeated flow events, each separated by a period of retreat, with each subsequent flow failing to travel as far down the hill. This in turn suggests that each active period either had less snowfall or lasted a shorter period of time.

The craters in this image add weight to the buried ice glacier hypothesis. The football-stadium-sized crater near the top left appears filled with ice, while the two smaller holes to the right look like each impact hit soft slush that simply melted away as the bolide drilled itself down, leaving no rim. Why there is such a difference between the look of these impacts needs to be explained. The two smaller ones might occurred at the same time, when the condition of the ice was the same, but that’s only a guess.

Higher up the repeated flow events appear to be eroding away, with gaps and depressions between them, which also fits with the belief that these glaciers are presently either inactive or sublimating away.

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