Monday, January 11, 2016

Hoodoo you do? Tent Rocks, New Mexico


-Alison

If you are a nature or geology enthusiast and get a chance to go to New Mexico, I promise, you will not be without things to do and see. For many of us New Mexico is also a great place to eat yourself sick on chile (green, red, or both!) and sopapillas, but it is also home to some epic landscapes. I’ve been traveling to NM with my family for decades and we usually found a way to sneak in something scenic: Taos Gorge, lava tubes, White Sands and more. More recently I’ve been to NM for purely geologic reasons, hitting key volcanic locations like Valles Caldera and Ship Rock.

This last November I had the chance to hang out for a few days with a preeminent mapper of New Mexican volcanoes, and his equally impressive geochemist wife. I was there to look at pyroclastic rocks from the last ~1.6 million years and quarries that might let me get some of these rocks (in large quantities) back to New York. My colleagues and I at the University at Buffalo are in the early stages of doing some experiments on how pyroclastic flows behave and want to use natural volcanic materials. Some days it feels like I am trying to single handedly change the geology of western New York to be more volcanic… More on this in another post.
Pumice fall deposit between the two major units of the Bandalier Tuff. This was erupted through the Valles Caldera around 1.25 million years ago.  
Pyroclastic rocks are those formed by explosive eruptions (fire and fragments for a rough transliteration). In this case, the rocks I was interested in were pumice fall deposits that were formed when pumice rained down from a large eruption column at the beginning of a pretty big eruption. The eruption produced not only plumes, but also large pyroclastic density currents that formed thick deposits ash flow tuff or ignimbrite.  
Eruption of Cordon Caulle, Chile in 2011. This eruption column is full of ash, pumice, and other rock that was broken by the eruption (Wikimedia Commons).
In the area near Los Alamos these pumice beds are found at the bottom of eruption sequences that were sourced from the Valles Caldera including the Bandalier Tuff and El Cajete pumice. The pyroclastic density currents from these eruptions transported pumice, ash, and bits of rock over the landscape around the caldera filling in valleys and otherwise making a complicated landscape flat. Since then, the rivers have reestablished themselves leaving big bluffs of pink and white pumice and tuff.
The cliffs in the foreground are the Bandalier Tuff. They form flat plateaus that dominate the landscape. In the background is the edge of the Valles Caldera.
We drove around looking at the rock sequences and just drinking in the amazing landscape. After I learned what I needed to about the deposits themselves, my field assistant Robin and I headed to the Bandalier National Monument. Located just outside of Los Alamos the monument was set up to protect the landscape and the homes made by the Ancestral Pueblo people carved into the tuffs.

The dwellings, in what is now Bandalier National Monument, were multi-storied, had lots of interior decoration and would have been both well protected, and pretty well climate controlled (Photos by Robin Wham).
Even though I have been to many of these sites before, I never tire of seeing the desert light shift over the valleys and cliffs revealing new detail and reminding me how neat our planet is. This trip, however, I had enough time to add in a new stop on my itinerary: Tent Rocks.
Tent rocks are basically hoodoos, where the tough boulder protects the softer tuff (ironic naming huh?) and forms little tent shapes.
Kasha-Katuwe Tent Rocks National Monument is in central New Mexico, about an hour and a half north of Albuquerque. The cliffs are made up of layers of pumice, ash and boulders, which were emplaced by pyroclastic flows, and then redistributed by water and gravity. The rock still gets called a tuff, like the Bandalier rocks because they are made of mostly volcanic materials, but the Tent Rocks show lot of evidence of having been moved around after the eruption by water. Just imagine all the pumice and ash in the Bandalier Tuff, while some of it remains to make the bluffs and cliffs, a lot of it is missing. As the rivers reestablished themselves they moved large quantities of the ash, pumice and boulders downstream. Tent Rocks are only one of many examples of what downstream would have looked like. Since the material available to move was all volcanic, the river/debris flow/alluvial fan deposits downstream would be made up of nothing but volcanic rocks.
Tent Rocks are hoodoos, or eroded pillars of soft rock protected by a harder rock. In this case, the harder rocks are boulders that end up perched on top of soft tent shaped pillars of pumice and ash. The resulting shapes are pretty fantastic.
My favorite of the "Tents".
The main walking trail through Tent Rocks takes you through narrow gullies and puts you face to face with the rock. Robin and I spent a lot of time just staring at all the excellent structures preserved in the rocks.
 
My field duck provides scale next to a nice series of normal faults.

Erosive contacts between different units. This may have been a stream channel. (Photo by Robin Wham). 
 
The trees that make their home in the canyon are very committed.
The trail takes you to the top of the bluff where you get a 360 degree view of the Pajarito Plateau. In the distance to the north you can see the Jemez Mountains and the Bandalier tuff, and to the south Albuquerque.
Tent rocks in the foreground. The pink cliffs in the background are made of Bandalier Tuff and the snowy mountains are the Jemez Mountains.
The hike isn’t long, but requires some clambering and can be a bit narrow. I thought it was worth the few scrapes and scrambles and the non-geologists we chatted with on the trail seemed to think so as well.  
I do love me some volcaniclastic sediments.

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