A vocabulary of landscape — a landscape of words
1367 entries
fin
A fin is a long, narrow, freestanding wall of rock, tall out of proportion to its thickness, standing in parallel with others like a set of blades. Fins form where a rock body is split by long parallel cracks and the softer material between them erodes out, leaving the slabs. In the sandstone country of southeast Utah, they are the necessary first stage of an arch: the rock has to be thin enough to be perforated before it can be spanned.
Etymology
The word is Old English for the fin of a fish, and geologists borrowed it for the shape. It is one of a long list of landform terms that are just body parts and animal parts applied to country, alongside hogback, saddle, shoulder, neck, spur, toe, and brow. Rock climbers use it the same way, and so do surfers and pilots.
Notes
The fins at Arches National Park are Entrada sandstone, cracked when salt beds far below flowed and bulged, and later exposed as the rock above them stripped away. The Fiery Furnace is a maze of them. Not every fin becomes an arch; most simply thin, undercut, and come down, which is why the two thousand arches in that park are the survivors of a much larger population of possibilities.