To the Cape! (part 2), For real this time! Options

[Tesheiner]

This is a navcam mosaic taken after driving during sol 1559.


Mmm, remember the name of this thread?
To the Cape! Yeah!

[Shaka]

Ultimately, these questions all hearken back to the formation of the cape-and-bay crater rim. Why are the bays eroded down the strata at a 20 - 30 degree angle, while the capes are cut down more or less vertically. I can't believe that this is due to a more resistant sediment formation in the capes, neatly interspersed with less resistant strata in the bays. Until somebody lays out a plausible hypothesis for the formation of Victoria's sinuous rim, I don't think this little microcosmic curiosity at the base of one cape can be understood.

[ElkGroveDan]

Why are the bays eroded down the strata at a 20 - 30 degree angle, while the capes are cut down more or less vertically.

Primarily: Capes have greater exposure to the prominent erosion forces - prevailing winds. As a result they are in a less stable vertical condition. The bays are set back and more sheltered from the prevailing winds so they are older and have had time to slump. As an example go dig some holes in your yard, one each month. After a year see what the sides of the holes are like. The newest holes will have the steepest sides, the older holes will have slumped in on themselves.

Secondarily: The capes by virtue of their recessed shape are traps for the heavier particles that the winds are unable to lift from the crater.

This back and forth of capes and bays likely occurs in a manner analogous to a meandering stream. Over the eons the shapes will migrate back and forth as bays fill up and capes are eroded away...and the crater grows ever larger (assuming some external condition doesn't cause it to become filled in by migrating sand dunes or such.)

[PaulM]

This back and forth of capes and bays likely occurs in a manner analogous to a meandering stream. Over the eons the shapes will migrate back and forth as bays fill up and capes are eroded away...and the crater grows ever larger (assuming some external condition doesn't cause it to become filled in by migrating sand dunes or such.)

The problem with this argument if I understand it correctly is that the capes consist of ancient undisturbed strata and not the recent deposits you would see on the bank of a river. I think that the argument only works if Victoria crater is getting bigger at the same sort of rate that the capes are moving. Then there would always be a supply of fresh undisturbed strata from which to carve out the new capes.

[ElkGroveDan]

The problem with this argument if I understand it correctly is that the capes consist of ancient undisturbed strata and not the recent deposits you would see on the bank of a river.

It's not true that the deposits on the banks of a river are necessarily recent. Rivers cut through some very, very old layers just as the wind on Mars is doing. Take a trip to the bottom of the Grand Canyon. There are entire banks in places made of Vishnu Schist which is 1.7 billion years old. The same is true the world over. In fact the best way to locate old layers is to examine the banks of a river (when there is no convenient road-cut nearby.)