A recent video from the National Park Service explains the phenomenon, called surge flow, which occurs when melting snow from the creek’s nearby peaks cascades down onto the sand ridges, causing the sand to create underwater ridges which in turn produce waves that can occur as often as every 20 seconds during the spring and early summer.
According to Nicholas Scarborough, an educational ranger at the park, surge flow can only occur in places that have a sandy creek bottom free of any pebbles or stones.
The reason for this is because when the sand stands on its own, it begins to form antidunes when water cascades over it, creating little ridges below the surface where water pressure builds up that eventually create flowing waves when they finally release.
Since Medano Creek begins at snowfields that sit high in the Sangre de Cristo Mountains, when that snow begins to melt as temperatures rise, a surge of water kicks up in the shallow creek, making it an ideal location for activities like tubing and wakeboarding.
“It really looks like a beach party when you go down there,” Scarborough told Travel + Leisure. “People have tents set up where they’ll have picnics next to the creek, while kids splash around in the water and make sand castles and their own little dams out of the sand.”
That’s why rangers at the park refer to it as “Colorado’s natural beach,” with the base of the creek surrounding the park’s natural dunes creating quite the view.
Medano Creek is currently approaching its peak flow, according to Scarborough, and will dry up towards the end of July, giving you a bit more time to enjoy the fascinating natural effect in person.