If you’ve ever wondered whether the gaps between valley ridges were eerily even in their spacing, you’d have been right. Geologists have struggled to explain the phenomenon, or produce a predictive model to say how far apart those ridges will be over time.

Armed with some spectacular images like this one, (more below the fold) Taylor Perron at the Massachusetts Institute of Technology, Cambridge, US, has worked out what makes those ridges space themselves out so evenly. (press release). His research is published in Nature. It’s a combination of soil creep – which is the really slow downhill movement of soil that happens as gravity pulls soil and rocks into a more comfortable position – and the channels that streams cut into the sides of the valleys. These two processes do opposite things, the first smooths things out and the second chops them up.

The timescales that these processes work on are the key to the formula. When these two competing processes happen on the same timescale, there is a characteristic length scale for the valley ridge spacing.

Perron looked at five valley networks of different sizes – with spacing between valleys ranging from 30 to 320 metres. Using the formula he had come up with, he tested that it worked.

They also hint at why different-length spaces exist between ridges. This is affected by the soil and the climate – whether it is muddy and wet, or sandy and dry.

Images: Gabilan Mesa, California, Credit: Ionut Iordache (UC Berkeley) / Taylor Perron (MIT)