Field excursions to the Jemez Mountains, New Mexico

Abstract

Published as public domain, therefore reproducible without permission. Source credit requested.iii Preface This bulletin has been compiled from the field guides for two complementary and somewhat unconventional trips offered as part of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) General Assembly in Santa Fe, New Mexico, in June, 1989. One, a Field Workshop of the IAVCEI Commission on Explosive Volcanism, was pre-assembly trip 11WA to study ignimbrites and calderas of the Jemez Mountains, New Mexico, and the San Juan Mountains, Colorado. Only the New Mexico part of the original Field Workshop Handbook has been rewritten and updated here for this publication. The original Workshop Handbook was not prepared as a standard geologic road guide but more as a series of volcanologic explanations of individual outcrops, showing how each contributes to the overall picture of ignimbrite eruption and caldera evolution in the Jemez Mountains. Some minor stop omissions, stop sequence changes, and simplifications from the original 11WA Workshop Handbook have been made in this version to improve the field guide's general appeal.The field guide for White Rock Canyon was prepared for a 1-day-long trip to look at maar volcanoes along the Rio Grande. It is an unusual trip in that travel is by rubber raft. There are no odometer readings or road signs-descriptions are linked to side canyons along the Rio Grande. If you have your own raft, kayak, or canoe and know how to use it, you are ready to take this trip, which begins at Otowi Bridge along NM-4 (a permit is required from the main office of San Ildefonso Pueblo) or from Buckman Crossing, which is reached from Santa Fe (no permit required). Most rafters continue through White Rock Canyon to the boat docks at Cochiti Reservoir, where you leave the river. Plan for a very long day or camp along the river overnight. If you want to take the trip and have no way to float down the river, several of the northern New Mexican rafting companies occasionally have float trips through White Rock Canyon.On the raft trip, if you leave White Rock Canyon via the Frijoles (Upper Falls) trail, you are in Bandelier National Monument. Take no samples and pay an entry fee at Monument Headquarters (if someone is picking you up, they will have already paid the fee at the entrance).A few points should be borne in mind when following these field guides. Both trips present some degree of physical challenge, as the rafting and scaling of ignimbrite cliffs, while not requiring special preparation or equipment, are perhaps a little more demanding than usual field trip routes. Weather is another consideration for these trips, especially in the higher elevations of the Jemez Mountains. Unless it is an exceptionally precipitation-free winter, snow and harsh weather conditions are likely to prevail between November and March at many of the stops in the multi-day field guide, and bad snow storms can close much of the area as late as May.Access for the geologist on foot a...

Decay of ignimbrite fairy chimneys of Arizona's Basin and Range Province, USA

“…Columnar jointing is thought to be a first key step in the development of a fairy chimney (Pallister et al, 1997; Self et al, 1996). As tuff cools, columnar joints develop at right angles to cooling surfaces from a decrease in volume due to cooling; this then generates tensional stresses (Hetényi et al, 2012).…”