SAGE update

Summer of Applied Geophysics (SAGE): Update

By Louise Pellerin
Green Geophysics
SAGE Codirector

The Summer of Applied Geophysics (SAGE) just celebrated its 35th year! Over this time, more than 900 students and faculty have been studying the structure of the Rio Grande Rift with funding from the National Science Foundation, the U.S. Department of Energy, and many friends in industry including ExxonMobil, Chevron, Zonge International, Sensors & Software, Geonics, and many others. Industry support is still strong and consistent, but in these changing times we need to adjust the SAGE program and develop new affiliations. We are planning a smooth and natural transition to SAGE 2.0, and as part of our new plan, I have accepted the position of codirector, replacing retiring codirector W. Scott Baldridge, Los Alamos National Laboratory, and will serve with ongoing codirector Lawrence Braile, Purdue University.

SAGE faculty have taken pride in the close collaboration among academia, government, and industry. This diversity has provided a strong base of financial support and also provides the students with exceptional opportunities to spend time with professionals from industry and government and gain insight that can help them make choices on their career options within geophysics. We wish to strengthen our ties with industry and nurture new relationships within the U.S. Department of the Interior. We are looking to our endowments and various foundations to fill the gap in our NSF funding. SAGE is grateful to have an endowment at AGU; growing the endowment will be critical to the future of SAGE. It is going to take heavy lifting to move SAGE to a new paradigm, but it will be well worth the effort. I have many times heard from former students, “SAGE changed my life!,” and have seen the growth that has accompanied the changes. The majority of students find out about SAGE from alumni at their university, while others stumble upon SAGE, drawn to the idea of working outside in the beauty of New Mexico and have found their calling in geophysics. Either way, the fieldwork, along with processing, interpretation, and presentation of the data and the breadth of technical exposure at SAGE, opens their eyes and helps to refine their interests.

Paul Bedrosian and Darcy McPhee, scientists from the U.S. Geological Survey, have joined the SAGE faculty in recent years. In 2016, SAGE was invited to work with the U.S. National Park Service (NPS) on the Tyuonyi Ruins in Bandelier National Monument in New Mexico. Growing our relationship with NPS, SAGE acquired gravity data in 2016 and transient electromagnetic (TEM) data in the adjacent Valles Caldera National Monument. We are planning another few years’ work in the Valles during which we will acquire additional geophysical data including seismic and magnetotelluric soundings of this igneous structure with the aim of publishing a definitive study of the Valles. After that, the plan is for SAGE to move to another national park for several years of study.

I am happy to present the Tyuonyi Ruins study data, thanks to the work of SAGE 2016 and 2017 students, in particular

  • Team Tyuonyi 2016
  • Team Tyuonyi 2017
  • Andrew Wilson, San Diego State University
  • Chelsea Sica, University of Texas at Dallas
  • Sam Taylor-Offord, Victoria University
  • David Graham, University of Texas at Dallas
  • Alejandro Rosado, UNAM, Mexico
  • Emily Peacock, University of Texas at Austin
  • Phoebe Ly, University of Texas at Austin
  • Conrad Suen, University of Texas at Austin
  • Josie Gonzales, NAS-Flagstaff

who worked under faculty advisors John Ferguson, University of Texas at Dallas; and Darcy K. McPhee, U.S. Geological Survey, Reston, Va.; along with support from Jamie Civitello, National Park Service, Los Alamos, N.M.; Jordon Jarrett, National Park Service, Los Alamos, N.M.; and Greg Johnston and Chris Martin, Sensors & Software, Mississauga, Ont., Canada.

The Tyuonyi Ruins at Bandelier National Monument

The Tyuonyi Ruins are located in Frijoles Canyon at Bandelier National Monument, ~35 kilometers from Santa Fe, N.M. The site contains nearly circular pueblo ruins, kivas (circular subsurface ceremonial rooms), and cliff dwellings that were occupied between 1350 and 1550 CE by the indigenous people of the Frijoles Canyon on the Parajito Plateau (Powers, 2005). The canyon was abandoned near 1550 CE and briefly reoccupied in the 17th century. The main plaza measures ~38.1-42.7 meters in diameter. The 1908-1912 excavation by Edgar L. Hewett and the School of American Archaeology exposed some 250 ground floor room blocks (Hewett, 1909) built with stone (Bandelier Tuff) and cemented with mud mortar. The NW section of the plaza was left unexcavated, and the spoil was piled on the NE periphery. The goal of the geophysical measurements were to

  1. Test the utility of seismic, ground-penetrating radar, magnetic, and electromagnetic techniques for subsurface
    mapping at the Tyuonyi site
  2. Determine whether the construction of a new pathway on the NE periphery of the ruins interferes with any potential archaeological features
  3. Locate an old road believed to be close to a proposed pathway
  4. Investigate the NW section of the plaza to determine whether room blocks lie close to the plaza underneath the mound

1.1 Geology

The canyon is embedded between the SE flank of the Jemez Mountains and the Rio Grande (Powers, 2005) and has been carved over the past 1.22 Ma by the perennial flow of the Rito de los Frijoles Creek, which passes SW of Tyuonyi. The Otowi Member (1.61 Ma) and the Tshirege Member (1.22 Ma) constitute the 274-meter-thick Bandelier Tuff that originated from the Jemez volcanic field. Alluvial and colluvial sediments compose the base of the Canyon (Reneau, 2000). Qbt (Bandelier Tuff)–welded to nonwelded rhyolitic ash flow tuff that incises easily at the base of Frijoles
Canyon. Qal (Quaternary Alluvium)–gravel, sand, and silt deposits originate from the Pajarito Plateau; includes stream terrace and canyon wall colluvium. The alluvial drainage network along the eastern edge of the Tyuonyi Pueblo has changed over time.

1.2 Magnetics and Electromagnetic Induction

Total magnetic field measurements were taken on a 30×30-meter grid overlapping both electromagnetic (EM) grids. The grid was sampled from east to west heading north with a Geometrics model G-858 cesium vapor portable magnetometer along survey lines spaced 1 meter apart. Field data were not drift corrected because there was little to no diurnal variation observed during the time the survey was made. Shallow to moderate depth anomalies were found. The increase of field strength from SE to NW is most likely due to spoil and arroyo deposit location and thickness. Magnetic anomalies could be associated with looter’s pits or fire pits. Room blocks are seen as a ring of high magnetic field, and the lineation of weak but shallow magnetic anomalies could be related to the old road.

Measurements were taken on two 30×30-meter grids with a Geonics EM-31 instrument using 2-meter coil spacing. The southern grid was sampled from east to west heading north, and the northern grid was sampled from NW to SE heading NE; all grid lines were spaced 1 meter apart. The high conductivity close to the room blocks is due to the high clay content used in their construction and conservation, while lower conductivity father from the ruins is due to the 1908-1912 excavations spoil.

1.3 Ground-Penetrating Radar (GPR) and Seismic Reflection

Two 30×30-meter grids of GPR data were recorded along 1-meter-spaced lines using the 250-MHz Sensors & Software NOGGIN(R) 250 Smart Tow and processed using the EKKO Project V5 program. Processing methods were applied using EKKO LineView to display drainage channel evolution of the subsurface (line y29). A small portion of the proposed Main Loop Trail will overlap part of this drainage network. Seismic refraction data were collected using a 48-channel Geometrics Strataview recorder and seven spreads with 0.5-meter geophone spacing, a 6-meter shot point interval, and a hammer source. Shot point offsets between 0.5 meter and 48 meters provided overlapping subsurface coverage. Seismic data from SAGE 2016 and 2017 were merged into a 168-meter-long profile.

1.4 Results

Some archaeological features identified with the geophysical survey relate to Hewett’s description of the site (1909).  GPR and seismic interpretation suggest that the room blocks on the north part of the plaza are buried under the spoil. Whether the plaza was closed on the north or had an alternate exit remains an open question. The old road was not fully resolved in the survey. EM, GPR, and magnetic data show reworking of near-surface soil and rock in the spoils pile north of the room block. The GPR images and seismic model are used to interpret the Quaternary geology of the site. These data trace incision of the Rito de los Frijoles into the Bandelier Tuff over several stages of the canyon development. The seismic model indicates a number of narrow, shallow channels carved into a broader strath. Holocene alluvial terrace deposits overlie the Bandelier Tuff surface, and the Tyuonyi Pueblo was constructed on top of the highest terrace. On the north side of the Pueblo, coarse colluvium from the steep canyon walls interfingers with the alluvial terraces. In addition, there is an anthropogenic debris layer that coincides with the colluvium. The magnetic and EM data corroborate this model. The
geophysical data show no distinct archaeological structures beneath the proposed new trail.

1.5 References

Hewett, E. L., 1909, The excavations at Tyuonyi, New Mexico, American Anthropologist, New Series, v 11, p 434-455.
Powers, R. P., 2005, A grand and isolated place, in Powers, R. P., Ed., The Peopling of Bandelier: New Insights from the Archaeology of the Pajarito Plateau, School of American Research Press, Santo Fe, NM.
Reneau, S. L., 2000, Stream incision and terrace development in Frijoles Canyon, Bandelier National Monument, New Mexico, and the influence of lithology and climate, Geomorphology, v 32, p 171-193.