The Cerro Toledo Formation (CTF), a series of intracaldera rhyolitic dome complexes and their associated extracaldera tephras and epiclastic sedimentary deposits, records the dynamic interplay between volcanic, tectonic, and geomorphic processes that were occurring along the western margin of the Rio Grande rift between major caldera-forming eruptions of the Bandelier Tuff 1.65-1.26 Ma. The Alamo Canyon and Pueblo Canyon Members differ significantly despite deposition within a few kilometers of each other on the Pajarito Plateau. These differences highlight spatial distinctions in vent sources, eruptive styles, and depositional environments along the eastern side of the Jemez Mountains volcanic field during this ca. 400,000 year interval. Intercalated pyroclastic fall deposits and sandstones of the Pueblo Canyon Member reflect deposition with a basin. Thick Alamo Canyon Member deposits of block-and-ash-flow tuff and pyroclastic fall deposits fill a paleovalley carved into coarse grained sedimentary units reflecting deposition along the mountain front. Chemistry and ages of glass from fall deposits together with clast lithologies of sedimentary units, allow correlation of outcrops, subsurface units, and sources. Dates on pyroclastic fall deposits from Alamo Canyon record deep incision into the underlying Otowi Member in the southern part of the Pajarito Plateau within 100 k.y. of the Toledo caldera-forming eruption. Reconstruction of the CTF surface shows that this period of rapid incision was followed by aggradation where sediments largely filled pre-existing paleocanyons. Complex sequences within the upper portion of the Otowi Member in outcrop and in the subsurface record changes in the style of eruptive activity during the waning stages of the Toledo caldera-forming eruption.
Repeat aerial LiDAR imagery was acquired for the Frijoles Canyon watershed (~17.5 mi²) located within Bandelier National Monument in May 2010 and again in September 2013. This sequence captured landscape-scale changes that occurred as a result of the July 2011 Las Conchas wildfire which severely burned a majority of the upper watershed and left the area vulnerable to post-fire flooding. The largest flood occurred in response to an unprecedented multi-day precipitation event totaling ~8-inches (approximately one third of the annual rainfall), which generated a peak flow of ~9500-cfs on September 13, 2013. Numerous smaller rain events have also generated large magnitude runoff including a ~7000-cfs flood in August 2011 and a ~6000-cfs flood in July 2013. Erosional impacts include landslides, debris flows, scour of the main stem and tributaries, undercutting of canyon walls, development of rills on side slopes, and widening of the channel. Changes in drainage density, ruggedness, and gradient record the effect of reduced vegetative cover and elevated storm intensities on drainage morphology. Subtraction of the 2010 LiDAR grid from the 2013 LiDAR grid provides quantitative values for regions of scour and aggradation. Hydrographs, repeat photos, and footage of fire and floods complement the LiDAR imagery as a record of this sequence of catastrophic change.
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