IRIS PASSCAL Supports Fluvial Seismology Research in Grand Canyon
When and how do rivers transport sediment from eroding landscapes? New research by Brandon Schmandt and Karl Karlstrom of the University of New Mexico and Rick Aster of New Mexico Tech is shedding light on how seismology can address this fundamental problem. The PASSCAL Instrument Center provided several quick-deploy stations from its RAMP (Rapid Array Mobilization Program) pool in support of this innovative project. The panoramic view of the Grand Canyon above was taken during a December 2012 data recovery trip.
Constraining episodic and steady state transport of sediment is central to understanding how landscapes evolve and how to best manage water resources. Direct monitoring of riverbed processes is often impractical, but fluvial transport of water and sediment generates elastic waves in the solid Earth that can be monitored with seismograph stations outside the channel. To take advantage of a controlled flood from Glen Canyon dam through Grand Canyon during November 2012, short-period PASSCAL and NM Tech seismographs and infrasonographs sampling at 250 samples/s were deployed in close proximity to three stretches of the Colorado River. This flood event was part of a sequence of controlled episodes staged in recent years by water management and National Park authorities to redistribute sediment, including beach sand, throughout the Grand Canyon corridor for both natural habitat and recreational management. During November's flood the flow of the river was increased from approximately 8,000 to up to >45,000 cubic feet/s (224 to 1,260 cubic m/s) for several days.
UNM and NMT researchers and volunteers installed and recovered eight PASSCAL stations near Phantom Ranch, Hance Rapids, and Lee's Ferry. This effort required appreciable hiking, rafting, and engagement of the National Park's mule teams, but all was in place by the onset of the flood on November 18. The Lee's Ferry site was the only one that was accessible by vehicle; Hance Rapids seismographs were transported by raft and hiking, and Phantom Ranch sites were supported by hiking and mule train.
Initial analysis of seismographic and infrasonic data show very clear flood stage signals as well as pre/post flood changes in the river's seismic signals that offer unique opportunities to advance the nascent field of fluvial seismology. Understanding these signals and signal generation processes offer possibilities for studying flows that are too energetic to monitor by other means, or are hidden (e.g. in caves or below glaciers or ice sheets).
Acknowledgments. This project is a joint effort between the University of New Mexico and New Mexico Tech, with strong partnerships from Caltech, the Flagstaff AZ US Geological Survey Grand Canyon Monitoring and Research Center (GCMRC), and the National Park Service (NPS). Dirk Scherler (Caltech) is thanked for his vital contribution to the field deployment. Jack Schmitt, Carol Fritzinger, Nick Voichick, and Bob Tusso from the GCMRC are thanked for logistical support. Ellen Aster (University of Oregon) is thanked for assistance with seismograph recovery. Martha Hahn and Ronda Newton (NPS) made it possible to take advantage of this exceptional science opportunity in Grand Canyon National Park on short notice. Pnina Miller, George Slad and their colleagues at the IRIS PASSCAL Instrument Center are thanked for their efforts in instrument preparation, personnel training, and data recovery. The facilities of the IRIS Consortium are supported by the National Science Foundation under Cooperative Agreement EAR-1063471 and by the Department of Energy National Nuclear Security Administration.
Flow of the Colorado River at Lee's Ferry and Phantom Ranch (there is approximately 1 day of flow delay between the two sites), 10/21 – 12/19/12. Oscillatory variations reflect diurnal power cycling at Glen Canyon dam.
Panoramic view of Hance rapids showing flood remobilized debris fan from Red Canyon in the foreground.
Log-frequency spectrogram of vertical-component velocity power as a function of day-of-year for a station at Hance Rapids, showing multi-band and time-varying seismic excitation. River discharge is shown at right.
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