The Recipe for a Hoodoo
The otherworldly spires of Bryce Canyon are carved from the Claron Formation, a layer of sedimentary rock deposited in a system of ancient lakes between 30 and 60 million years ago. This formation is not uniform; it consists of alternating layers of different rock types, primarily limestone, mudstone, siltstone, and dolomite. This geologic layer cake is the key factor in hoodoo formation.
Two relentless processes work together to sculpt the rock: chemical weathering and physical weathering. Rainwater, which is naturally slightly acidic due to absorbed carbon dioxide, creates a weak carbonic acid solution. This acid slowly dissolves the calcium carbonate in the limestone layers, rounding the edges of the hoodoos and creating their lumpy profiles. The more dominant force is physical. At Bryce Canyon's high elevation of 8,000 to 9,000 feet, temperatures frequently swing above and below freezing. For more than 200 days a year, this freeze-thaw cycle drives a powerful process called frost wedging. Water from rain or melting snow seeps into vertical fractures in the rock, then freezes and expands by about 9-10%. This expansion acts like a wedge, exerting immense pressure and forcing the cracks wider, eventually breaking large sections of rock apart.