This blog is about hiking trips along the Valles Caldera Rim. For more information, see link for the Valles Caldera Rim Trail blog.

Saturday, May 30, 2009

Fraser Goff's Valles Caldera: A Geologic History

I appreciate Fraser Goff's book, Valles Caldera: A Geologic History. The book gives solid, science-based information on the creation of the Valles Caldera 1.25 million years ago as a result of the awakening of the Jemez Volcanic Field, at the intersection of the Rio Grande Rift and the Jemez Lineament. He gives reliable geologic dates for the creation of the Valles Caldera and the eruption between the resurgent dome and caldera wall of subsequent moat rhyolites, such as Cerro del Medio. (Quite interestingly, Goff says that Cerro del Medio, which erupted 1.23 million years ago as the first of the ten moat rhyolite complexes, may have been created in six different eruptions.)

Fraser's book, published May 2009, wasn't out when I posted a photo narrative on selected trail segments of the Valles Caldera Rim in late 2007 (see VCR Blog Archive, November 29-December 3, 2007). For geological dates, I relied on a publication of the New Mexico Geological Society, Geology of the Jemez Region II, Fall Field Conference, Volume 58, 2007 and any abstracts of geologic research papers that I could find online.

While I enjoyed immensely the opportunity to explore the Valles Caldera Rim, the fact remains that I'm no geologist. Frankly, unless it's painfully obvious, like a rockslide, I struggle with trying to understand the story behind the rocks and landforms I see. It's as though it is hidden from me albeit in plain view. Also, the geology research papers that I read, well, it's debatable how much I understand because of the technical language used. That's why it's such a delight to read Fraser Goff's Valles Caldera: A Geologic History because he intelligibly interprets the geological underpinnings of the landscape of the Valles Caldera yet doesn't over-simplify or over-whelm.

The beautifully designed book has 114 pages and 52 figures, including many attractive color photos taken by Fraser Goff, sketch maps, charts, etc.. The figures are plentiful and do a great deal to increase understanding. The book is information dense yet concise. Goff includes the most up to date geologic information on the Valles Caldera, including some of the research done since 2000 when the United States government purchased Baca Location No. 1 and it became the Valles Caldera National Preserve. A brief, helpful glossary of geologic terms used and a bibliography for those who want to read more is included.

Recent research highlighted in the book includes a study of South Mountain lake deposits in the Valle Grande that may help climate change researchers to better understand climate variability in the Southwest. Dating of the 2004 core sample of the lake deposits revealed that South Mountain Lake persisted in the Valle Grande for over 200,000 years and this period spanned "...two complete glacial-interglacial cycles in the late Quaternary."

Goff says that new geologic mapping of the four USGS topographic quadrangles that cover the Valles Caldera - Bland, Redondo Peak, Valle San Antonio,Valle Toledo - is being done and will be completed in 2009 or 2010. This was done at the behest of the Valles Caldera Trust, in cooperation with federal and state agencies. In addition to being useful to the Trust for planning purposes, the new geological mapping has revealed more information about lake history in the Valles Caldera. Goff outlines the various caldera lakes that existed over four periods, beginning immediately after collapse of the Valles Caldera 1.25 million years ago and up to the most recent, 55,000 years ago, a short-lived lake caused by the El Cajete pumice eruption that blocked the East Fork of the Jemez.

I haven't even begun to do this book justice. It's worth reading and rereading. Chapter titles like The Next Valles Eruption and Where Does the Magma Come From and Is There More? give an idea of just how intriguing the book is.

Basically, Goff's book, written by a retired Los Alamos National Lab geologist who is currently an adjunct professor in the Department of Earth and Planetary Sciences at the University of New Mexico, is an excellent source to find the most accurate, enlightening geologic information on the Valles Caldera, located in Valles Caldera National Preserve in northern New Mexico. To meet the man in person, sign up for a Valles Caldera National Preserve geology van tour, which Fraser gives, alongside his geologist wife, Cathy.

Under Acknowledgments, Goff thanks Robert Parmenter,Preserve Scientist, Dennis Trujillo, Preserve Manager, and "...other members of the Valles Caldera National Preserve for their support and funding on this project...". It's wonderful to have a book like Fraser Goff's Valles Caldera: A Geologic History that reveals some of the science that is taking place at the Valles Caldera National Preserve. The Valles Caldera Trust is to be commended for their role in helping Fraser Goff to bring this book to the public. It's especially valuable because it makes clear what a treasure we all have in the Valles Caldera National Preserve. Goff calls the Valles Caldera "...perhaps the world's best example of a resurgent caldera, a giant circular volcano with an uplifted central floor." The geological wonder of the Valles Caldera National Preserve rises far above any importance it may have as a mere cow pasture and working ranch.

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Los Alamos, New Mexico, United States