[X] My Assistant

[ngunn]

The new 'looking ahead' with T39:
http://ciclops.org/view.php?id=4689

[Juramike]

Here are some graphics I whipped up of the T39 RADAR Swath section shown in PIA10219.



The first graphic shows estimated drainage pattern based on dendritic pattern orientation. Broadly, it is pretty much to the N, towards the Mezzoramia basin. But along the swath there are several drainage basin divides – almost like the surface shifted or dropped down into a series of puckers. Each pucker has its own little dendritic pattern. The broad patterns are indicate by the big blue arrows. The stream channels are indicated by red arrows. There is an orange area indicated that just doesn’t seem to fit in – more on this later.



The T39 Swath hit the SW section of Mezzoramia basin and the T7 Swath hit the N end of Mezzoramia basin. If the T7 Swath is turned upside down so that the drainage direction lines up, there are some similarities, as seen in the second graphic. One is that there are sediment filled puckers (or “dropouts”) like are seen in the T39 Swath. The only difference is that the puckers are filled with darker sediments in T7 and in the T39 swath they appear to have been subject to erosion so they have cute little dendritic patterns. Another similarity is that the RADAR bright sediment pattern near the basins appears simiar in the two swaths. This is seen in the following three slides:





The first slide shows the T7 bright pattern as one moves downstream near the basin (from left to right). The next two slides show similar patterns and are seen in the T39 Swath. The stream becomes bright on hitting the basin, then fans out and is criss-crossed by several dark lines. The RADAR brightness slowly fades on going further into the basin, possibly indicating sorting of materials over a very large distance. (Indicating extensive reworking?





The T39 RADAR Swath image shows a nice spectrum of different valley/ridge widths. An evolutionary sequence is shown in the graphic above. It all starts with an easily erodible upland, which is down cut into a karst-like terrain (image 1 and 2). The valleys perhaps hit a harder layer (maybe the erodible stuff is organic shizzle and the hard layer is “normal” crust/clathrate?) and then begins to widen (image 3). As the valleys widen, the ridges become sharer and narrower. (images 4 and 5). In image 6, very thin ridges remain which have been partially buried in infilled material. The locations where these images were plucked from is shown in the second graphic.




So presumably the thicker the intervening highland, the younger and less eroded the surface. Or, the thinner the ridges and broader the valleys, the older the surface. Since the “dropouts” or puckers seem to have only gentle alluvial networks, they seem to not have been heavily eroded. Perhaps they are made of different materials or they are much younger.


The last slide shows a zoom of the area around the orange indicated feature. Across the surface, there appears to be a uniform graduation of valley/ridge networks going from thin intervening ridges towards the south to thicker ridges (less eroded) towards the N central part of the image. The one exception seems to be where the orange-bordered terrain loos like it recently dropped out and filled in, messing up the uniform pattern. And perhaps that’s what happened. There was a slightly raised area that was subjected to erosion, then it suddenly collapsed and filled in. There does not appear to be any valley networks rushing into this new sinked area, although the bright line in radar indicates a substantial cliff. Other pucker areas seem to be located at drainage divides, thus the original surface prior to collapse must have been locally slightly higher. (Are these collapsed cryovolcano caldera??) This could be giving us a clue about the formation of at least the smooth type of lake, as well as some of the large dropout areas seen in W Xanadu, T7, and in the northern polar regions.

-Mike