Shiprock, New Mexico

September 15, 2012

Shiprock2012IMG_1253a (2)

: Dr. Jack B. Share 
Summary Author: Dr. Jack B. Share

September 2012 Viewer's ChoiceShiprock gives the impression of having been volcanically thrust out from the sands of the Mancos desert, but this isn't the case. Shiprock is indeed a volcano but of a class called a diatreme, having formed explosively from gas-charged magma escaping at great velocity. It possessed a crater at the surface called a maar, but erosion has long since removed it along with much of the sedimentary strata through which it erupted. What we see now is the solidified plumbing that remains called a neck and its system of magma-radiating conduits called dikes. Thus, Shiprock is a partially-exhumed, erosionally-sculpted diatreme.

The entire Shiprock volcanic complex emplaced between 28 and 19 million years ago during the Late Oligocene to Early Miocene. Its maar crater is estimated to have been located 3,250 ft (991 m) above the present day land surface of the Mancos Shale. That means Shiprock erupted through most, if not all, of the Late Cretaceous Western Interior Seaway’s sandstones and shales as well as some overlying Tertiary sandstones. The tectonic forces that created the uplift of the Colorado Plateau were likely responsible for the diatreme’s placement within the Navajo Volcanic Field and its subsequent exhumation and erosion. Photo taken on July 5, 2012.

Photo Details: Camera Maker: Canon; Camera Model: Canon EOS 7D; Focal Length: 69.0mm; Aperture: f/8.0; Exposure Time: 0.0040 s (1/250); ISO equiv: 100; Software: Adobe Photoshop Elements 5.0 Windows.