fissure

Over the ages, powerful forces such as frost wedging and exfoliation will cause scales or sheets of rock to split away from the face of a cliff. Eventually these rock scales may become completely detached and fall to the ground, but before that happens they can remain partially affixed to even a very steep precipice for millennia. While still in situ they are known to climbers and geologists as flakes. Flakes can be as small as a dinner plate, or they can measure thirty feet thick and encompass as much vertical terrain as a basketball court. Sometimes particularly large or distinctive flakes are given names that gain wide usage; Boot Flake, for example, which is shaped like a huge gumboot, towers fifty feet from heel to cuff, and tenuously adorns the upper southeast face of Yosemite’s El Capitan.

Jon Krakauer