Wouldn't wind be a more likely culprit than water?

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þeodcyninga, þrym gefrunon,
hu ða æþelingas ellen fremedon.

There doesn't seem to be anything missing to me. Observe the large raised area just "south" of the Mons in the newer image. Compare its location to the so-called sister Mons in the Viking image, and I'd say that's your culprit. It's less striking because of the rather steep angle the Viking image appears to have been snapped at.

Okay, I think I've found this one as well.

Note, in the Viking images, that the gash appears some distance to the right of the small central Mons, the last in that crescent of mounts from the left of the images. If you trace the 'gash' downward, you come to a rather recognizable section of the canyons "south" of the feature. (To clarify, it's a circular canyon almost the shape of a human eye. Oh no! )

Now, examine the newer image. To the right of that mount, and above that same feature, you can make out a ridge, as if there's a sharp change in elevation between the "west" and "east" portions of the land. You can actually follow this ridge from A9 down to the 'eye' in D8. Then, follow the canyons to the left, and you'll see the ridge pick up again in E4, where it continues "west" into E3 and then "south" into F3, off the map.

I'd say what we're looking at is some kind of natural ridge, or other steep elevation change in the landscape, rather than an actual gash. If I had to guess (and it's a wild one), the "western" half of the image may have once been a sea bed, and the elevation change is either the shoreline or the 'continental shelf'. That's sheer speculation though.

Already pointed out as the 'eye' feature. It's not diminished at all, simply the Viking images have thrown shadow onto the feature enough to make it seem larger, as well as blurring the outline of the feature which makes it more difficult to objectively determine its size.

My personal theory (as a non-geologist) is that we may be looking at a coastline, accompanied by a river delta (the canyons in the lower-middle of the image). The Mons' would then be islands (or underwater peaks) in an ancient sea bed.

As I said, though, this is really just a layman's look. I see no evidence of major erosion between the two images, and any water that existed on Mars would have been gone long before even the first one was taken, in order to create such features.

This is the point I was "trying" to make in my post. Any "oceans" on Mars have been dried up for a long long time. Certainly oceans didn't "spring up" and then disappear between the time these two images were taken.

Thanks, Kesh for making it "a bit clearer"...and a belated welcome to the board!

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"The facts gentlemen, and nothing but the facts, for careful eyes are narrowly watching." Isaac Asimov

Kesh, look closer at my post.

The long ridgeline you describe is evident in both, and not the feature in question. Just to the left of the "eye" is a valley shaped like a boot. Looks kinda like Louisiana. Just above it the valley looks a bit like Arkansas. The left ridgeline of the valley is just about under the 7/8 line.

The "missing gash" is right through the middle of zone D7. In the Viking image there is a change from bright to dark. There appears to be a distinct ridge line.

In the MOC image there is not a distinct ridgeline like a cliff. However, elevation does not appear to be flat. I contend that the image quality of the Viking mosaic is too poor to make valid comparisons.

I changed the picture so it now has several possible areas of change that FieryIce and I have noted for starters. That should help keep down the future confusion.

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It's not what you know or don't know, but what you know that isn't so that will hurt you. Will Rogers
http://www.craterchains.com/ns/nspage.html

Here's my take on this "analysis." The whole comparison is ridiculous on it's face, since we are being urged to compare a low resolution, poorly controlled, hand-built photomosaic with a digital topographic relief basemap.

However:
A: Apparent ridge on Viking in Fortuna Fossae. Mostly an albedo feature. Visible on Themis basemap if you go to the site, click the map onto Albedo and zoom in a bit.

B: Ophir Chasma. No difference obvious. Zooming in both the Topo and Albedo Basemap
shows nothing you wouldn't expect from differing resolutions, illuminations and data types.

C: Duplicate Arsia Mons in Viking mosaic. Obvious mosaicking error. There are plenty of Viking era images of Arsia Mons and it's always been a single volcano.

D: Tharsis Tholus. No differences you wouldn't expect from different data sets.

E: Crater Fesenkov. Seen in Viking era. Likely off the Viking map shown.

F: Echus Chasma. No differences you wouldn't expect from different data sets.

G: Lunae Planum. Viking shows E-W albedo trends. Themis topo base map shows N-S structural trends. Themis basemap shows the E-W albedo markings also when toggled to "Albedo" intead of "Relief"

H: Kasei Valles. Valley with outflow channel landforms. No differences you wouldn't expect from different data sets.

I: Ceraunius Fossae. The N-S trending tectonic structure doesn't show particularly well in the low res albedo map, but does in the topomap, since they are primarily topo features. Viking saw the structure at higher.

J: Crater Poynting. A low relief crater, the Viking Mosaic does not capture it well, but other Viking imagery does.

Every single putuative difference pointed out is either no difference at all, obvious cartographic errors in older datasets, or misinterpretation of datasets which are meant to show completely different things.

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Irishman, I apologize. I must have misunderstood what you were pointing to. And it appears craterchains agrees with me as to the gash/ridge in my conclusion, as now the "gash" and the "ridge" are both labeled object F.

Though I have to admit, craterchains, I'm a bit upset. It's not cool to switch photos midway through the thread like that. And how did you manage that, anyway? Hosted on a site of yours?

Either way, could you put the originals back, and post new links to the labelled photos? That way, we can see clearly what this discussion is about.

That said, Irishman, I'm still not sure what object you're pointing out, if you're not referring to object F. I'll keep examining the original Viking photo, but I'm just not seeing it right now.

{Edit} Okay, I see what you mean, now. It appears to be the object craterchains has labelled A. Is that correct?

Thanks! I've been lurking for several months, and just recently decided to start posting. Wanted to get a feel for the board first.

Hopefully, I can make some good contributions to the board. I'm just a layman with some amateur experience and a few classes, but hopefully that's good enough I don't make a complete idiot of myself. 8)

Starting out a "tad" off topic, but I'll "tie" it back in...I promise.

I think you'll find that this is the best board on the web, IMO. (I was "lucky" in that this is the first board I'd ever posted to, and now I'm spoiled.)

That's the beauty of this board...we have folks here rangeing from interested pre-teens, to seasoned scientists...and though I'll offer my opinions, (at the drop of anyone's hat), the most important aspect of this board, IMO, is the fact that there is a lot of learning going on here. (I know I learn something new here "almost" every day).

Don't worry, I make an idiot of myself at least once a week. (HEY, you, in the back, stop laughing.)

And what is this board "about"?...I think that craterchains "case" is the perfect example. (See, I've "wandered" back on topic...told ya all I would.) He has proposed that there were "catastrophic" changes on Mars, taking place within a 30 year period. As "evidence", he provides 2 images. Yet, he doesn't seem to take into account the fact that these images were taken by spacecraft whose technologies are separated by 30 years.

It's just as Eye-Zee posted. We're being asked to compare 2 images of differing resolutions, etc. and make conclusions based on that. I'm beginning to wonder what we would see if we had sent another Viking to Mars, in the late 90's, and taken images of the same area. I'm willing to bet that they would look "essentially" the same. The "differences" in the images are "basically caused by" the "differences" in the spacecraft and differences in processing. There's really no mystery here...at least no "objective" evidence of one.

Everyone is welcome on this board...but...

If a person comes here, and has a "theory" that supposedly reflects reality, then the folks here are going to want to see some evidence that the "theory" isn't so much hot air.

IMO, craterchains has not been able to provide that evidence. His "imagined differences" in Martian geography are more than likely simple differences in resolution.

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"The facts gentlemen, and nothing but the facts, for careful eyes are narrowly watching." Isaac Asimov

Kesh, yep, point A. No problem, just keeping on the correct feature.

Eye-Zee, nicely done.

Sorry about the image change taking a few by surprise, for conservation of band width, both here and at our site, please download the photos to your desk top for perusal off line.
Here are a couple links that will help, and there are literally hundreds of photos available with searches for them. We only post a couple relevant ones for topic starters. We are not trying to lead anyone down any particular path, EXCEPT one of personal discovery. As stated, we are still acquiring and examining photos for relevant possibilities of changes. If any are interested in pursuing this, and not so lazy to search for photos instead of having it all handed to them on a silver platter with a silver spoon to eat with, they will find some great food for the mind and the satisfaction of self discovery.

I am in Seattle for a couple days working at a high-speed connection as at the boat in Tacoma I only have 26.4kbs speeds. Will adjust the photos when I get back to the boat and provide the first image set we put up. Please copy to your desktop, as we will be changing that one photo to a couple others as we progress with this investigation. No theory, no case, and questioning many things before anybody should state anything as yet. Agreed it could be just the differences between imaging techniques, could be. Or is it really a difference in actual changed image content? :-?

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It's not what you know or don't know, but what you know that isn't so that will hurt you. Will Rogers
http://www.craterchains.com/ns/nspage.html

Well, I've personally discovered that this thread is going "nowhere".

No, not really. You're "theory" just isn't that interesting.

Wait a minute...you've come here with a "theory"...it's up to you to prove it. We're not going to do your "work" for you.

Oh that's just great! So at any time you can change the images, to suit your whim? I don't think so.

Resolution!!

Well, or course the image content is "different", but that's not all you're saying. You're saying that there is actual geologic changes evident when you don't have the data to support that contention.

I liken it to myself...trying to read small print without wearing my glasses. Is the print on the page the same even though it "looks" out of focus to me?? Well, of course it is!

The same kinda thing applies here, IMO. It's your job, craterchains, to prove that "differences in resolution" can not be the cause of the "perceived differences". So far, you have not done so.

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"The facts gentlemen, and nothing but the facts, for careful eyes are narrowly watching." Isaac Asimov

My .02

There is no way to resonably compare the two images that isn't purest speculation. There is simply no way to differentiate between what might be compression artifacts, noise in the original image or who knows what. A cursory comparison isn't even really possible without the same picture geometry. They're not even the same type of image!

You might as well try to compare a polorid taken from a hot air baloon and a landsat near-infrared image, and try to find the "Changes", it's simply bad science.

Thank you all for your comments.
I have decided against further discussion until better image interpretation data can be obtained.

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It's not what you know or don't know, but what you know that isn't so that will hurt you. Will Rogers
http://www.craterchains.com/ns/nspage.html

Yes, nice. Of course, I get to see images like that (except farther east) at work "all the time." Animated, too! 8)

Darn. I guess I don't get to mention how much difference it made to our satellite interpretation techniques when the resolution was increased quite significantly when the latest GOES came on-line.

Or do I?

Hmmm... I see that "craterchains" has been banned. Oops....

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"I am Meteora, supreme goddess of weather" - Meteora, in The Unchained Goddess

One nice thing about being a meteorologist who also likes astronomy is that the sky is always interesting!

Well, his partner in these "investigations" and the poster who started this thread...fieryice is still here...maybe she'll be willing to discuss this "stuff".

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"The facts gentlemen, and nothing but the facts, for careful eyes are narrowly watching." Isaac Asimov