Globally rare natural phenomenon at Great Sand Dunes this month

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GREAT SAND DUNES NATIONAL PARK AND PRESERVE, Colo. — While the dunes at Great Sand Dunes National Park and Preserve are the main event, the shallow creek at the base features a natural phenomenon rarely seen in any other part of the world.

It’s called surge flow, a stream flowing in rhythmic waves on the sand.

According to the park website, as water flows across sand on Medano Creek, sand dams form on the creek bed and gather water.

When the water pressure is too great, the dams break, sending down a wave about every 20 seconds. Waves can surge up to a foot high.

June is one of the best times to see this phenomenon, but expect long lines of traffic into the park, overflowing parking lots and booked campgrounds, park officials said.

Because of a cold and wet May, peak flow is happening a little later than average this year, park officials said.