Boarder Blake Nielson was shredding at Big Cottonwood Canyon in Salt Lake City, Utah when an isolated wind slab broke loose above and below him ... which knocked him to the ground and "took me for a ride."

Nielson -- who says he tested the Kessler Peak area for instabilities before his run -- was able to stay above the surface as the snow shot him down the slope ... using swimming motions with his arms and kicking his board to keep from going under.

In the video, Nielson is heard yelling over the radio to his partner ... saying, "Logan, I'm sliding!! ... I'm staying on top, but I am sliding!!"

Nielson predicts he was swept about 300 feet before he was able to come to a complete stop ... and the slope slid around 1,300 feet.

In Nielson's report of the incident, he says it's imperative to respect the wind.

"Even a small 'manageable' wind pocket can break and carry you a long way in steep terrain with long runouts," Nielson told the Utah Avalanche Center.

He also learned cross-loading is something to look out for ... as he did not expect it to be that big of a problem.

Nielson also suggests making a ski cut ... saying had he done so, he could have decreased some hazards.