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USGS Geology in the Parks

Devils Postpile National Park Geologic Story

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leaning columns


In postglacial time the Devils Postpile has changed greatly. The huge talus pile of broken posts is evidence that the lava columns extended many feet in front of the present face after the last glacier melted. The prying action of water freezing in the cracks between the columns has probably been responsible for most of the fallen posts. The present rate of falling is sporadic and uncertain. A 1909 photograph showed three of the columns leaning far ahead of others in the formation. These were separated from nearby vertical columns by as much as 12 inches at the top. Although they appeared ready to fall, these three leaning columns did not topple even during the strong earthquakes in the summer of 1952.

During May of 1980, intense earthquake swarms occurred at an epicentral site about two miles southeast of the community of Mammoth Lakes. This eastern Sierra community and the surrounding area were shaken by an unprecedented series of earthquakes that included four of a Richter magnitude of 6.0 within a 48-hour period.

Lesser earthquake swarms accompanied by sporadic tremors continued throughout the summer of 1980. On July 7th the leaning columns tumbled down. Numerous other columns in the formation were cracked, and today rest precariously on their severed bases. Small earthquakes continue to contribute to the mechanical weathering process of the Postpile formation- columns continue to fall at an unpredictable rate. Columns that have fallen recently can be detected by looking for lighter shades of newly-exposed unweathered rock surfaces on the downed columns.

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Material in this site is adapted from a pamphlet, Devils Postpile Story, by N. King Huber, USGS, and Wymond W. Eckhardt, NPS. It is published by Sequoia Natural History Association, Sequoia Natural History Association, HCR-89, PO Box 10, Three Rivers, CA 93271-9792, Telephone (559) 565-3759.

 

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