30 December 2017
Flying from Albuquerque to Denver last summer, en route to Montana from the Earth Educators’ Rendezvous, I flew over a landscape that looked like the geomorphology was controlled by normal faulting. The view here is looking to the east, from a position in the air a bit north of Albuquerque:
…Zooming in closer on the set of parallel valleys that appear to be controlled by normal faulting:
Today, I was cleaning out my camera’s memory card in anticipation of next week’s Structural Geology and Tectonics Forum, and I saw these photos again. I considered them, noting the north-south trend of the faults, which struck me as likely to be controlled by tectonic extension along the Rio Grande Rift. I went to Google Earth to see if I could find the place, and sure enough, I was able to:
The arrows show my east-west extension hypothesis.
But the Google Earth view didn’t confirm for me that the cracks were faults rather than joints. I needed a geologic map for that.
Zooming in, you can see the little “lollypop” icons coming off the faults – this indicates normal faulting and tectonic extension:
The “lollypops” are on the down-dropped (hanging wall) side of the fault.
The NGMDB also allowed me to find a Geologic map of the Albuquerque – Rio Rancho metropolitan area and vicinity by S.D. Connell (2008), which labeled this faulted plateau as the San Felipe Volcanic Field:
The New Mexico Bureau of Geology and Mineral Resources labels the plateau itself as Santa Ana Mesa:
So it looks like crustal stretching east-west along the Rio Grande Rift opened up a series of north-south trending faults. This stretched the crust east-to-west, but also tapped into magma, which was brought to the surface and erupted as the San Felipe Volcanic Field. Additional later extension broke the volcanic rocks in more north-south trending faults, and then erosion etched out those, making a series of horsts and graben(s), and accentuating their parallelism into the surface of the Santa Ana Mesa’s land surface.
This to me is a very satisfying thing to be able to do: to notice something out an airplane window, then track down the details through a series of open-access publications on the web, and come to a better understanding of the place.