Sunday, August 23, 2009

Time Almost Beyond Imagining: Who Do the Magic that Hoodoo?

Sorry for the title. Sometimes such things are irresistable, and geology terms sometimes seem to lend themselves to parody: subduction, orogeny, bedrock, schist and gneiss. Just the same, today's post is about one of the stranger places in the Colorado Plateau country: Kasha-Katuwe Tent Rocks National Monument on the flanks of the Valles Caldera, site of the previous post on the latest part of the geological story of the Colorado Plateau. It's got a lot of unique scenery packed in a small area.

The Valles Caldera is one of the nation's active supervolcanoes, and over a period of more than six million years, the eruptions of the center have blanketed the region with rhyolite tuff and ash. If you look at a physiographic map of the caldera you can see that erosion has sliced into the flanks of the volcanic complex, exposing evidence of older eruptions. The scenery at Kasha-Katuwe is the result of this geologically recent erosion of the soft volcanic rocks.

Some of the layers on the flanks of the caldera contain river and mudflow deposits with boulders and cobbles of all sizes. The larger boulders protect the softer underlying rocks from erosion until the boulders stand at the top of tall pillars (see the third picture). These are hoodoos. Eventually the boulders topple, and erosion attacks the underlying rock, producing the strange conical spires that give the monument it's name (the English part anyway; Kasha-Katuwe refers to "white cliffs" in the Keresan tongue). The erosion of the soft rock by flash floods in this arid environment have also led to the formation narrow steep-walled slot canyons (the fourth photo).

The monument is a bit tricky to find; the park brochure and location map can be found here. The New Mexico Bureau of Geology and Mineral Resources has a nice review of the geology of the region. If you ever pass through the Sante Fe-Albuquerque region on a field trip, check it out!
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