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Eruptive history in Rio Grande del Norte National Monument

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NMBGMR graduate student Jacob Gehrz inspecting a basalt sample in the Rio Grande gorge northwest of Ute Mountain, near the Colorado border. Jacob is standing on a clay-dominated paleosol that was buried by the lava flow to his right. By dating that lava flow (a piece of which is in his hand), Jacob will be able to constrain the time at which the soil was forming. While the gorge here is much shallower than it is farther south, we still don't want to pack out unnecessary or potentially contaminated samples (in addition to the 8-pound sledgehammer at his feet), hence Jacob's close inspection of this specimen before it passes muster.
(click for a larger version)
Kevin Hobbs

Taos County, NM
— September 23, 2021

In 2013, President Barack Obama invoked the Antiquities Act of 1906 to create the Rio Grande del Norte National Monument in Taos County. Part of the wording of this 115-year-old act allows for the protection of features of "scientific interest that are situated upon the lands owned or controlled by the Government of the United States", of which there are many in the Rio Grande gorge and surrounding canyons and volcanoes. Since 2017, I have collaboratively studied sediments in between lava flows in the gorge. With help and expertise from colleagues from UNM, UC Boulder, and the NMBGMR, we are working toward better understanding of the paleoenvironmental conditions that existed during the ~2 million-year-long eruptive history of the Taos Plateau Volcanic Field during the Pliocene Epoch. We're also refining the timing and duration of individual eruptions, as well as gaining insights into the fluvial evolution of the Rio Grande, Red River, and alluvial fans draining the Sangre de Cristos and Tusas Range.

Kevin Hobbs, Field Geologist, NMBGMR

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UNM Earth and Planetary Sciences Professor Karl Karlstrom, NMBGMR student Jacob Gerhz, and NMBGMR Senior Geochronologist Matt Heizler at an enigmatic intertrappean deposit of basalt cobbles in the Rio Grande gorge near Questa. The team had just collected sands from this deposit for detrital sanidine age dating, a specialty of the NMBGMR Geochronology Lab.
(click for a larger version)
Kevin Hobbs
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A 6 meter thick intertrappean deposit near Cerro Montoso. NMBGMR graduate student Jacob Gehrz is taking in the view atop a rockfall boulder in the center of the frame. This light reddish-brown sediment deposit is observed in the walls of the gorge for over 8 km, from near Cerro Chiflo to at least the Red River confluence. Jacob and I were at the site to describe the sedimentary and pedogenic features within.
(click for a larger version)
Kevin Hobbs