Hoodoo (geology)

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Thor's Hammer in Bryce Canyon National Park

Hoodoos are tower-like structures made of sedimentary rocks in western North America that were formed by erosion . They are relatively common on the Colorado Plateau and the Great Plains . Bryce Canyon National Park is considered the region with the largest number of hoodoos in a small area in the world .

Hoodoos are found mainly in arid and semi-arid climates. They can reach heights of 1.5 to 45 meters. Unlike normal rock needles, hoodoos have a characteristic "profile", that is, the circumference of such a more or less round rock tower increases and decreases at more or less regular intervals from foot to top. The resulting shape is reminiscent of a totem pole . The reason for this shape is the build-up of sediment layers of different hardness. The tip in particular consists of such a hard layer that largely protects the rock needle from erosion from above. Because different minerals are stored in the different layers, the color of the hoodoos also changes with height, usually between white and different shades of red.

Emergence

Hoodoo Formation.jpg

The plateau into which the Bryce Canyon was cut consists mainly of limestone , with intercalated carbonate siliciclastics and dolomite stone . They are petrified sediments from an extensive lake that covered a large part of Utah in the Eocene , about 40 million years ago . The sediment sequence is referred to as the Claron Formation (Wasatch Formation, the "Pink Cliffs" of the Grand Staircase ), the no longer existing lake as Claron Lake . The dry-fallen Claron Lake Basin was raised to the current level in the Miocene and Pliocene around 15 to 5 million years ago along with the rest of the Colorado Plateau. As a result, today's landscape emerged.

The formation of the rock towers from the sedimentary rocks of the Claron Formation occurs through physical and chemical weathering and the removal of loose material through wind and rain. It is of particular importance that the rock is criss-crossed by a network of cracks and crevices, so-called fissures . Around 200 night frosts per year ensure that water penetrating into fissures freezes, enlarges the crevices and increasingly weakens the rock ( frost splitting ). Rain by carbon dioxide uptake from the air slightly acidic is preferably dissolves the limestone and the carbonate , which the siliciclastic sedimentary rocks holds on. The starting point for the actual hoodoo formation are narrow protrusions in the plateau wall, called fins (literally “fins”) in English (referred to as “lamella” in the figure above). During the weathering and erosion of these protrusions, the decomposition of the rock progresses fastest at the fissures, which is particularly evident in the formation of ice windows (" ice windows "). With progressive weathering and erosion, such a protrusion is finally transformed into a row of free-standing pillars. The differences in the relative weathering resistance between pure limestones, the siliciclastics and the dolomitic layers ensure the development of the characteristic hoodoo shape on each of these pillars.

Capitol Peak in Palo Duro Canyon ( Texas Panhandle ) with hoodoo-like tower rock at the tip of its southern foothills, siliciclastics of the Quatermaster Formation (Permian) and Tecovas Formation (Triassic) of the Llano Estacado .

The most famous hoodoos in Bryce Canyon are "Thor's Hammer", "The Hunter" and "Queen Victoria".

literature

  • Frank DeCourten: Shadows of Time. The Geology of Bryce Canyon National Park. Bryce Canyon Natural History Association, Bryce Canyon 1994, ISBN 1882054059 .
  • Eugene P. Kiver, David V. Harris: Geology of US Parklands. 5th edition. Wiley, New York 1999, ISBN 0-471-33218-6 , pp. 522-528.
  • Douglas A. Sprinkel (Ed.): Geology of Utah's Parks and Monuments. Utah Geological Association, Salt Lake City 2000, ISBN 0-9702571-0-4 , pp. 37-59.

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