The Pinacate Volcanic Field
Quaternary basalt volcanism in Northwestern Sonora, Mexico
Pinacate is the finest of the many monogenetic basalt volcanic fields in the Cordillera of western North America. The volcanoes are monogenetic, not the fields, each was built in one short eruption and is related to its neighbors only by its location and by the uniform processes of magma generation. Composite volcanic mountains created over long periods of time by sequential eruptions from evolving magma bodies also occur in many of these fields. Pinacate has Volcan Santa Clara, a rare Trachyte Shield Volcano (on the horizon). Magma interacted with water to create steam explosion hydro-volcanoes in some of these fields. Pinacate's steam explosion maar-calderas (Sykes Crater above) are the most spectacular of such craters outside of Africa. Pinacate may be close to an active plate boundary where mid-ocean ridge basalt is being generated, but its rocks are predominantly alkali-basalts, more akin to rocks from the other monogenetic fields rather than to rocks of the mid-ocean ridges.
This site build is preliminary and contains the introduction, the geologic setting, and descriptions of some volcanoes. Click on thumbnails that show the pointing finger cursor to access galleries of images.
Monogenetic basalt volcanism features many cones of different ages scattered apparently randomly across the landscape. This sunrise photograph from the space station shows Pinacate cones standing in sharp relief above their lava flows with the shield of Volcan Santa Clara standing above them all. Pinacate's three largest maar-calderas form a line down the middle of NASA image ISS004-E-12326.
The second photo in this gallery shows typical pyroclastic cones, best described as ordinary volcanoes.
A gallery of Pinacate images to entertain your curiosity. You can scroll through with your mouse wheel or click on the right to next, on the left to previous. The diagonal arrows on in the icon at the top will expand the image to its full size on your monitor allowing use of scroll bars to see detail.
Ask the expert: This website is Dan Lynch's Pinacate book. Color photographs look better on a screen than on a printed page and the price is right. I am telling the story of Pinacate geology in the photographs, their captions, and accompanying text. Click on the smaller images and most will expand to fill the browser window. Some are links to galleries of images. The double diagonal arrow in the icon at the top will expand the image to its full size (1200 px wide or 900 px high); you may have to scroll to see it all. Visit about for more information about the site. I hope I have layered this site appropriately for the geologists, volcano enthusiasts, and Pinacate people for whom it is intended. PLEASE - send me an e-mail and tell me how to improve it.
Biosphere Reserve: Pinacate and the surrounding Gran Desierto de Altar dune fields were given Biosphere Reserve status under the United Nations in 1993 and are now administered by the Comision de Areas Naturales Protegedas. Their headquarters is at Ejido Nayarit near the Highway 8 bridge over the Rio de Sonoyta and they have a spiffy new visitor's center, Schuk T'oak, on the Ives flow south of Sierra Blanca.
Pinacate is the black oval on the tan sand at the head of the Gulf of California. It was as obvious in the first picture of Earth from space made from a V-2 rocket in 1945. lavas and cinders are intermingled with sand from the Gran Desierto de Altar blown in from the Colorado River Delta by prevailing westerly winds. This links to its Geologic setting.