Great Sand Dunes experiencing rare, natural phenomenon

Medano Creek at the Great Sand Dunes National Park is peaking this weekend.

Medano Creek at the Great Sand Dunes National Park is peaking this weekend.

It's flowing in braided channels - each about 10 to 40 feet wide and 1 to 20 inches deep, according to the National Park Service website.

Medano Creek is one of the few places in the world to experience "surge flow" - a stream, flowing in rhythmic waves on the sand.

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Three elements are needed to produce the phenomenon: a relatively steep gradient to give the stream some speed, a smooth creek bed with little resistance, and enough water to create surges.

In spring and early summer these three things combine to make waves at Great Sand Dunes.