[X] My Assistant

[Bob Shaw]

One of the pre-MOLA hot topics was the supposed discovery of ancient Martiian shoreline features of various forms in, for example, Viking images. Now we have accurate height measurements, high quality MGS images, MOLA, and THEMIS data, and the whole subject has gone rather quiet, despite MEX images which are allegedly of glaciation and the remnants of ice floes.

I drove today from Glasgow to Gourock and back, and saw a 20 mile long raised beach; where are the Martian raised beaches?

Bob Shaw

[Guest_AlexBlackwell_*]

From what I understand, Erin Kraal et al. have a paper, Quantitative geomorphic modeling of Martian bedrock shorelines, that should be published online in JGR-Planets early next week. Here's the crux from the abstract: "In light of these results and the difficulty of maintaining warm, wet climates on Mars, it seems unlikely that the putative shoreline features identified in images are a result of water wave erosion, and alternative hypotheses, such as ice cover, should be entertained."

[tty]

From what I understand, Erin Kraal et al. have a paper, Quantitative geomorphic modeling of Martian bedrock shorelines, that should be published online in JGR-Planets early next week. Here's the crux from the abstract: "In light of these results and the difficulty of maintaining warm, wet climates on Mars, it seems unlikely that the putative shoreline features identified in images are a result of water wave erosion, and alternative hypotheses, such as ice cover, should be entertained."

Floating ice can be a very powerful erosional agent. "Strandefladen", a characteristic bedrock platform along the Norwegian coast is thought to be largely due to ice erosion. Another characteristic glaciomarine erosion feature that might be worth keeping in mind on Mars is iceberg plowmarks which can be very large.

tty

[Bob Shaw]

Floating ice can be a very powerful erosional agent. "Strandefladen", a characteristic bedrock platform along the Norwegian coast is thought to be largely due to ice erosion. Another characteristic glaciomarine erosion feature that might be worth keeping in mind on Mars is iceberg plowmarks which can be very large.

tty

Google throws up zip on that one - any pointers?

Those scottish raised beaches are Late Glacial or Early Holocene, i. e. about 10, 000 years old.

tty

It's a bit more complicated than that, but yes, they're not very old. The raised beach I mentioned is generally agreed to have been created by isostatic uplift, post-glaciation, and is a dramatic 50 mile linear feature all along the Inverclyde coastline and down to Ayrshire. There are other Scottish raised beaches which have more specifically glacial origins.

Bob Shaw

[tty]

Google throws up zip on that one - any pointers?
It's a bit more complicated than that, but yes, they're not very old. The raised beach I mentioned is generally agreed to have been created by isostatic uplift, post-glaciation, and is a dramatic 50 mile linear feature all along the Inverclyde coastline and down to Ayrshire. There are other Scottish raised beaches which have more specifically glacial origins.

Bob Shaw

Sorry, it should be "strandflaten", I mixed up Norwegian and Danish spelling.

Raised beaches aren't created by isostatic uplift. They are upraised by it. There are plenty of them here is Scandinavia too, thanks to the postglacial isostatic rebound. There are presumably plenty of glacial beaches elsewhere too, but the postglacial transgression has drowned them.

tty

[Bob Shaw]

Sorry, it should be "strandflaten", I mixed up Norwegian and Danish spelling.

Raised beaches aren't created by isostatic uplift. They are upraised by it. There are plenty of them here is Scandinavia too, thanks to the postglacial isostatic rebound. There are presumably plenty of glacial beaches elsewhere too, but the postglacial transgression has drowned them.

tty

I think we know what we mean re the raised beaches - and presumably whatever uplifted Tharsis might have left some such, somewhere.

As for the strandflaten, I'm off to dig through my geomorphology textbooks - I'd always had the impression that skerries etc were features of glacial deposition rather than erosion, and yes, the effects of grounded sea-ice/glaciers *would* be impressive agents of erosion! Mr Holmes, where *are* you hiding?

Bob Shaw

[dvandorn]

Mr Holmes, where *are* you hiding?

Come now, Watson, you know my methods -- simply apply them.

First, we observe rocks on the surface, which have obviously been eroded by aeolian forces for millions, if not billions of years. Second, we see massive erosion of landforms -- upon which sit rocks which seem not to have moved for millions, if not billions, of years.

By process of elimination, we can see that aeolian forces, even over billions of years, could not have been the sole erosive force acting upon Martian landforms.

Whatever remains, however unlikely, must be the truth...

-the other Doug