ALAMOSA, Colo. – This is the best time of the year to experience a globally rare natural phenomenon at the sand dunes in the San Luis Valley, according to a Great Sand Dunes National Park and Preserve spokesperson.

Medano Creek is now approaching what’s called “surge flow,” a phenomenon where creek water flows in waves across the sand.

The combination of a sufficiently steep channel, a sandy creek bottom and plenty of flowing water only exists in a few places on Earth, according to the spokesperson, “and Medano Creek is considered the best place in the world to experience surge flow!”

Because of the unusually cold and wet conditions in May, peak flow is occurring a little later than average this year, the spokesperson said.

You can follow detailed creek conditions and forecast flow on the National Park Service website.

The video below, courtesy of the Great Sand Dunes National Park and Preserve, shows you exactly what happens during surge flow: