Several forces of nature have played a hand in the formation of Bryce Canyon’s horseshoe-shaped amphitheaters, and other similar formations in the surrounding region. While much of the landscape is the result of millions of years of changing climates and shifts and uplifts of the Colorado Plateau, the hoodoos that stand sentry in Bryce Canyon today are largely the result of a combination of wind, water, and ice erosion.
Bryce Canyon’s unique geologic history dates back to the Cretaceous Period, more than 100 million years ago when a shallow sea, along with ancient lakes and streams that later covered the region, deposited layers of shale and sandstone sediment. The colorful deposits are visible today in the Claron Formation showcased throughout much of Bryce Canyon. The Pink Member of the Claron Formation, highlighted in Bryce Canyon’s colorful hoodoos, is largely composed of limestone, a soft sedimentary rock that is particularly subject to erosion.
The primary force behind Bryce Canyon’s formations is ice erosion, in a natural phenomenon known as frost wedging which occurs when rain or melting snow seeps into the limestone’s crevices and freezes. The expanding ice widens the vertical joint planes found in the Pink Member of the Claron Formation. Freeze/thaw cycles occur hundreds of times each year in Bryce Canyon, constantly changing the shape of the formations.
Chemical weathering is another force that shapes the hoodoos. It occurs when water such as rain or melting snow naturally mixes with carbon dioxide to form carbonic acid, which shapes and smoothes the formations. Wind has played a smaller part in Bryce Canyon’s erosional formation in comparison to the dramatic effects of water and ice.
Additionally, a mixture of mudstone and silt inside the limestone affect its horizontal erosion (as well as providing fertile ground for trees to take root, appearing to grow out of the rocks). These horizontal layers are more resistant to the effects of carbonic acid and dissolve at a slower rate, eroding in phases of fins, then windows, until hoodoos are all that are left standing. Some hoodoos are covered in dolomite, a more durable magnesium-rich limestone that protects the softer sediment beneath it.
The phenomenal forces of erosion that have shaped Bryce Canyon’s magnificent hoodoos will also destroy them someday; the hoodoos erode about two to four feet every century.