The entrance to Antelope Canyon in northern Arizona; one of the most famous slot canyons in the Southwestern U.S. These nearly vertical, extremely narrow canyons have been carved by flash floods in the Navajo Sandstone found on the Colorado Plateau. Image credit: Bret Webster; Bret’s Facebook and Web pages
They’re fun to explore but can be deadly during the summer monsoon season because there are few routes that allow a quick exit in the event that a flash flood advances downstream. I think it’s fascinating how the flow patterns are reflected in the sandstone, revealing all kinds of fluid dynamic perspectives, including vortex shedding, boundary layer separation, turbulent flow, and laminar flow.