Late Spring

As thaw proceeds, the pit floors and surrounding level plateaux are defrosted first, while snowpack persists in the alcoves and on some sheltered slopes. Then, over critical period of a few weeks, dramatic changes occur:

While thick snowpack is still present in the sheltered alcoves, suddenly a series of dark threads or ribbons appears. These occupy the centres of channels and sprawl across the distributory fans in spidery networks. They are not the shadows of the channel walls, but are much darker and crisper features a few pixels wide in the exact centres of the channels. They are a few metres wide (given the pixel dimensions) and intensely dark. They superpose (are laid on top of), or cut through patches of clear white snow.

Note also that diffuse avalanching appears in the central portion of M0903898

Better images of these can be seen here:
M0903898 (Full image from Malin Space Science Systems - Here)
M0905128 (Full image from Malin Space Science Systems - Here)
M0906352 (Full image from Malin Space Science Systems - Here)

See also:
M1001115 (Full image from Malin Space Science Systems - Here)
 

Two interpretations are possible:

It may be that pre-existing dark streaks, which we see in the Summer images, have preferentially thawed through the overlying snowpack. However, one would expect this to occur in a patchy, blobby, inconmsistent pattern, working in from the edges of the snowpack - rather like this sort of feature which is often seen as snowpack melts in "normal" polar areas.

What I prefer as an interpretation is illustrated here: i.e. that a fresh flow has occurred down the channels, and has either bulldozed the snowpack aside, or carried it away downhill, or dumped debris on top of it - or probably a combination of these things all at once.

I recommend that you inspect carefully the images that show this phenomenon and make your own mind up about what you are seeing. I admit that the features are subtle but I suggest that the set of images as a whole are more suggestive of flow events than of defrosting of pre-existing channels.
 

So, having seen the images, and thought about the dark streaks. If they are active flows, then what conditions are they flowing under?
 

Read on...

      Created: May 2002
      Last modified: May 2002
      Authorised by:  Head, Earth Sciences

      Maintained by: Nick Hoffman
      Email: nhoffman@unimelb.edu.au