August 19, 2009

A Rille That Doesn't Know What To Do with Itself

image from LROC Browse Gallery, ASU and NASA

Lavas flow downhill, but sometimes they don't seem to be in a hurry. This 600-700 m wide rille twists and turns like a kid told to go to bed. On Earth many rivers (of water) do the same thing when they flow across very gentle slopes. With such slopes downhill is well defined from a distance, but on the surface, minor deviations in topography swing the flowing liquid helter and skelter. Water flowing around the outside of a bend goes fast and erodes the bend. Over time adjacent bends intersect, cutting off a loop which becomes an ox-bow lake. Meanders in rivers take time to develop, but in the completely different case of lava flows can develop almost instantly. This rille is the famously illusive one on the floor of Schröter's Valley, the biggest rille on the Moon. Rilles within rilles occur a few places on the Moon, and it seems that the inner one is usually tightly meandering. Presumably the inner rille forms from a later eruption that sends lava flowing down the gently sloping flow surface of the first channel.

Chuck Wood

Technical Details
Moreinterpretation of this rille.

Related Links
Rükl plate 18

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