Dendritic ridges self-organize on an undercut barchan dune slip face

Dendritic ridges

I came across a beautiful barchan sand dune at Ocean Beach in San Francisco after a very windy period.

Diagram of a barchan sand dune

The slip face of the dune, being at its angle of repose, had formed a gorgeous slump — a most successful failure! — which can be seen left of center in the first photo below.

After photographing the slump, I began to experiment with slightly undercutting small portions of the base of the barchan dune slip face.

This would cause sand to avalanche from the upper edge of the disturbance, producing a mesmerizing effect: gullies such as in the lower center would slowly migrate to the top of the slip face, as can be seen to the left and right.

When the sand settled, often taking many minutes, dendritic ridges remained.

(Click on any photo to enlarge. Lighting is from the left.)

Self-organizing dendritic ridges on the disturbed slip face of a barchan sand dune.

Could undercut slip faces be an earthly explanation for how dendritic ridges formed on Mars?

The Dendritic Ridges of Valles Marineris

The Dendritic Ridges of Olympus Mons

The Dendritic Ridges of Olumpus Mons 2

Dendritic Ridges — Eye of the Beholder

The Thunderbolts Project is even offering cash prizes for experimental electrical demonstrations of the formation of Martian dendritic ridges.

Solving the Mystery of Dendritic Ridges — Innovative Experiment Prize

Natural Philosophy Alliance > Solving the Mystery of Dendritic Ridges

I started a thread at the Thunderbolts Forum proposing a simple, non-electrical explanation of the formation of Martian dendritic ridges:

Recreating “Martian dendritic ridges” here on Earth?

You decide. Below are more photos of dendritic ridges on the San Francisco sand dune. (Click on any photo to enlarge. Lighting is from the left.)