The Shiprock of New Mexico

Aug 7, 2015 0 comments

Shiprock or "the winged rock" in Navajo, is a monolith composed of resistant volcanic rock that rises nearly 500 meters above the high-desert plain of the Navajo Nation in San Juan County, New Mexico, United States. The monolith is the remnant of an ancient volcano that became extinct about 27 million years ago and has eroded away leaving a rocky stump exposed at the surface. The stump represents the neck of the volcano, the central feeder pipe through which the magma erupted, now solidified. This neck was probably 750 to 1000 meters below the land surface at the time it was formed, and has since gained its prominent form due to erosion of surrounding rocks.


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A striking feature of Shiprock are the dikes, or wall-like sheets of lava that radiate away from the central neck. These formed as magma rising upward from the underling magma chamber filled cracks in the ground during a period of eruption. Having cooled and crystallized in the fissure, the resulting rock structure formed a dike. Like the neck, these hard rocks are also relatively resistant to erosion, and thus stand above the horizon as massive walls of lava. There are at least six dikes that radiate away from Ship Rock.

Shiprock is composed of an unusual, highly potassic magma composition called a "minette", which is believed to result from extremely gradual melting of mantle rock. This is a material composed of smaller rock fragments cemented together, similar to conglomerate but with sharper, more irregular pieces. The jagged fragments hint at the explosive nature of the eruption that created Shiprock.


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Shiprock from about a mile away. Photo credit


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The rock walls on the left of Shiprock is part of a dike. Photo credit


Dikes radiating from Shiprock. Photo credit


Dikes radiating from Shiprock. Photo credit


Aerial view of Shiprock and the dikes. Photo credit


Aerial view of Shiprock and the dikes. Photo credit


Dikes from the distance. Photo credit


Dikes from the distance. Photo credit


Close-up of a section of the dikes. Photo credit


A section of a dike. Shiprock is seen in the background. Photo credit


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Sources: Dr. Vic Camp (San Diego State University) / New Mexico Bureau of Geology & Mineral Resources / Lawrence Kuss (Emporia State University)


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