bouncing boulder

• by wassock moderator

  This is neat. In the greyscale .jpg image the dark streak runs horizontal at halfway down. You'll need to enlarge to see it - and it is pretty fab if you can use Hiview

  http://www.uahirise.org/ESP_014394_2045

  Posted April 29, 2014 11:17 PM

• by p.titchin

  At last! a long Mars boulder track! Great image. Nice to have a scale as well. A 6 meter boulder Quite an impressive bowling ball! Wonder what the gradients are. ~Pete

  Posted April 30, 2014 9:29 AM

• by JellyMonster

  What an amazing image!

  Posted April 30, 2014 4:13 PM

• by wassock moderator

  Must be pretty steep - the boulder doesn't look overly rollable ( though I guess it could be vaguely cubic) but from the scale on the greyscale .jpg it has travelled around 1500 metres.

  More sums for those of you out there who are so inclined - if you have the same lump of rock falling down the same slope , one on Earth and One on Mars, which travels furthest? I'm figuring that gravity will be the major thing which has an effect, obviously air resistance will be less on Mars but not sure that will make too much difference. Pondering along the lines of if gravity is less then acceleration down the slope will be less, but so will the friction from contact with the surface, so it will be slowed down less - does that mean they both still roll the same distance?

  Posted April 30, 2014 4:14 PM

• by Kitharode moderator

  Hmmm ... Might have a go at that when we've sorted the 'halfway' moon thingy. 😉

  Posted April 30, 2014 4:41 PM

• by wassock moderator

  And another thing - The area where the boulder has bounced along has very few craters in it whereas the mid to lower right of the image and to the left beyond the ridge are both quite heavily cratered. further down the image the cratered-ness comes up fairly close to the ridge.

  This implies that the scree (for want of a better term) slope that the boulder has rolled down is a younger surface than the cratered bits and also that erosion in the particular area has increased in rate comparatively recently and more so than at other points along the ridge.
  If erosion was constant then you'd see a gradation of age (as indicated by number of craters) as you move further away from the cliff (areas close to the cliff will be covered up by bits falling off quicker than those further away. In the rolling boulder area there is a step change from lots of craters to hardly any - so that whole area has been "screed upon" comparatively recently at an increased rate to what has gone before.

  I'm assuming that most of the area right of the ridge line is made of pretty much the same stuff as the streaks don't seem to care if the surface is cratered (old) or 'smooth' (young).

  Also there are quite a few boulders in the nearby area most of which appear to show a tail down slope, analogous to the break in the dark streak caused by the rolling boulder. Might this indicate that at some time all of them have had a streak flow around them?

  Posted April 30, 2014 4:56 PM

• by p.titchin in response to wassock's comment.

  I think I remember from the moon boulder studies that frictional angle of the surface soil had a big influence, though I think the researchers were using the boulder tracks in different sites to calculate the differing frictional angles, and thus the differing soil density at the different sites.To do that, I guess they had worked out the sums for the gravity etc, I think I'll try a trawl of their studies tomorrow. ( I like looking at their rolling boulders anyway!) 😃 ~Pete

  Posted April 30, 2014 8:30 PM