I love Santa Fe, New Mexico, so when I had the opportunity to give a lecture on the Colorado River for Southwest Seminar, we spent an extra few days exploring the region. My colleague Kurt Kempter invited us to see firsthand the results of his pandemic project to create detailed maps of the maar volcanoes southwest of the city. These landforms form when magma interacts with groundwater to create steam explosions, forming shallow depressions after the explosions. The depressions fill with scoria (cinders) and lava flows, sometimes becoming lava lakes, and subsequent erosion can reveal the later volcanoes of the maar volcanoes. Maar formation creates depressions, but because the modern landforms are mountains (the filled lava is more durable than the surrounding material), it can be hard for beginners to understand.
Santa Fe’s historic plaza is located at the western end of the Santa Fe Trail. A wooden building visible in the center of the plaza conceals an obelisk and pedestal that was erected in 1867 to commemorate the survival of the Union after the Civil War. However, on one side of the obelisk, “THeroes who fell in various battles with the savage Indians in the New Mexico territory.In 1974,Barbarian” was chipped away by an unknown individual. On October 12, 2020, the obelisk was The monument was toppled, and the city began a community discussion about the monument’s future.
We always visit the little town of Chimayo to buy a year’s supply of red and green chili powder. The Virgil store shown here had a “For Sale” sign hanging in front of it. How horrible!
At Santuario de Chimayo.
On a lovely, clear day, Kurt took us to Diablo Volcano, southwest of the city, where he completed a detailed study of the volcano’s history and formation processes.This is a view looking west down the Diablo Canyon, carved out by the intermittent flow of the Cañada Ancha.
Google Earth image of the Santa Fe area. The city and Sangre de Cristo mountain range are on the right. The Cerros del Rio volcanic area and Diablo volcano are on the left. When I visited Santa Fe, I never explored the southwest part of the city. I’d been to the east, north, south, and west, but the hills to the southwest of the city always intrigued me. I’d also been intrigued as to why Santa Fe developed in the relatively featureless alluvial plain at the foot of the mountains, far from the Rio Grande. I’d always wondered why the Camino Real was off the river and up the alluvial plain (where important pueblo villages were located). But what was there between the city and the river? I soon found out.
A close-up of a Google Earth image. A broad alluvial plain is carved into the Tesuque and overlying Ancha formations. Notice how Diablo Volcano is partially bisected by Cañada Ancha, which is a big part of this story and will be revealed below.
Begin your trek to the volcano’s summit at Diablo Canyon Recreation Area, a popular spot for rock climbers who find the columnar joints in the canyon walls fascinating.
Along the way, volcanic bombs were scattered on the ground, proving that in this case the event occurred below the surface.
Western view of Lengua del Diablo (Devil’s Tongue). Note the bottom of Cañada Ancha on the far left, and Jemez Mountain and caldera on the horizon. The colorful rocks on the Lengua del Diablo ridge are composed of ash deposits from maar explosions (low greenish cliffs formed by phreatomagmatic explosions), overlain by dark basaltic lava, scoria, and ash (center of photo) that erupted after the maar formation. Note the vertical dyke within the phreatomagmatic explosion deposits. This dyke event actually fed the flow at the top of the cliff. Within the phreatomagmatic explosion deposits are very large chunks of the Tesuque Formation that were thrown outward by the phreatomagmatic explosion. One of these large pink pieces can be seen at the base of the green cliff and to the left of the dyke (partially hidden by a small juniper tree, a surprising exposure).
A large dyke (center) intrudes into the older scoria layer.
Complex interplay of maar ash (golden) and post-maar volcanic scoria and dikes.
A close-up of the previous photo, showing a dark basalt vein cutting through the old volcanic ash (golden in color).
From the top of the Marl, you can see the Jemez Mountains and Chicoma Peak to the west, with Cañada Ancha visible in the valley floor.
Panoramic view with Kurt Kempter pointing out features.
Another view of Lengua del Diablo. After a few hours of observing inside the volcano, I became interested in the circumstances of the eruption. Kurt explained that the age of the Cerros del Rio volcanic field is constrained to between 2.7 and 2.4 million years ago, straddling the Pliocene-Pleistocene boundary. Kurt further explained that the sequence of events was an initial phreatomagmatic eruption that formed a maar depression, which led to the formation of a scoria cone, which then led to the formation of fluid lava flows and a lava lake. In the back of my mind, I kept thinking, “Why are we higher than the surrounding terrain?” The answer, of course, was that 2.5 million years ago, the maar top was at the valley floor, and erosion of Diablo Canyon had not yet begun.
And this was clear when we went to the rim of Diablo Canyon. Beyond Diablo Canyon and Cañada Ancha is a detached section of lava lake basalt that once filled the central maar. It was separated from the foreland by river erosion. Diablo Canyon is therefore about 2.5 million years old.
Close-up of the far mesa. Note the small bump on the top of the mesa. It is made of rounded boulders and sand that were carried down from Cañada Ancha as it flowed over the lava lake. The flow did not know that it was on the edge of the lava lake deposits, and would not be deflected by the downward scraping. This is superposition in action. We are fortunate that these boulders remain on the high mesa for this interpretation.
From the top of Diablo Canyon, looking southeast and upstream to the bed of the Cañada Ancha River. Spectacular.
Quilt and his dogs look out over the Sanger de Cristo Mountains from the top of Maar Volcano.
Our group gathered at the end of the hike – Helen, Kurt, and John. Thank you Kurt for a great day and a wonderful site visit! Kurt will be publishing a paper on his research soon and will add an addendum to this post when it is ready.
