A.D. 1064? A Pilot Study Of Archaeological Tree-Ring Samples To Search For Visible Evidence Of The Eruption Of Sunset Crater Volcano, Northern Arizona

Summary

The tree-ring dating by Terah Smiley in 1958 of the eruption of Sunset Crater Volcano to the year A.D. 1064 was crucial to the interpretation of the archaeology, geology, and paleoecology of Wupatki and Sunset Crater Volcano National Monuments and the northern Southwest United States in general. Significantly, this was also the world's first calendrical dating of a prehistoric volcano eruption, creating a new application for tree ring data. The dating of the Sunset Crater eruption was based on the observation that tree-ring growth on several beams used in the construction of the prehistoric Wupatki Pueblo was first suppressed and then complacent following A.D. 1064 (Smiley 1958). This date has since become highly entrenched in the archaeological and geological literatures, as well as in popular accounts of the eruption. It is safe to say that the great majority of school-aged children in the Southwest United States know, without a doubt, that Sunset Crater erupted in A.D. 1064.

However, recent archaeological research, combined with increasing scientific sophistication, suggests that A.D. 1064 may not be accurate because: (1) Smiley based his A.D. 1064 date on changes in tree-ring samples from eight beams used in the construction of Wupatki Pueblo, a 100+-room masonry pueblo located approximately 20 km north of Sunset Crater. A reexamination of Smiley's samples indicates that most are duplicates from the same tree, with only three samples (two Douglas-fir and one ponderosa pine) actually showing ring suppression at A.D. 1064 (Elson et al. 2002, 2005, 2006, 2008; Ort, Elson, Anderson, Duffield, and Samples 2008; Ort, Elson, Anderson, Hooten, Champion, and Waring 2008; Robinson et al. 1975). Today, such a small sample size would be considered inadmissibly weak evidence for a scientific determination of this magnitude; (2) the original source area of the three Wupatki tree-ring samples that show this pattern is unknown because the site is situated around 20-30 km north of the nearest pine and fir trees; and (3) this unique tree-ring pattern of suppressed followed by complacent rings has not been observed again in any other sample and is distinct from tree-ring patterns caused by historic or modern volcano eruptions (see Boston 1995; Elson et al. 2005; Sheppard et al. 2005, 2008, 2009).

The pilot study undertaken here intensively examined 39 prehistoric dendro-archaeological samples from Wupatki Pueblo and the Sunset Crater area to determine whether there were visible signals in ring morphology that could be used to support, refute, or refine the A.D. 1064 date. Significant advances in tree-ring analytical methods since 1958 make this re-analysis feasible. Thirty-nine samples are an acceptably sized data set for scientific publication, and provide sufficient evidence of whether volcanoes can be dated using visible ring-widths and other signs of tree-trauma, either alone or in concert with modern chemical techniques.

Significantly, our research suggests an eruption date for Sunset Crater Volcano of sometime between A.D. 1085 1090, and not A.D. 1064 as Smiley (1958) previously determined. Additional data from two other research projects, one supported by the National Science Foundation (Sheppard et al. 2004, 2008) and the other by Western National Parks Association (WNPA Grant #2005-14; Elson et al. 2009), provide additional supporting evidence for the results of this study. However, as discussed in greater detail below, it is important to note that the data are not entirely conclusive and more research needs to be undertaken before this issue can be resolved with certainty.

This Resource is Part of the Following Collections

• Desert Archaeology DAHA Resources   •
• Digital Archive of Huhugam Archaeology (DAHA)

Keywords

Temporal Coverage

Calendar Date: 1080 to 1090 (Tree ring narrowing dates in 24 out of 26 samples)

Calendar Date: 1060 to 1070 (Tree ring narrowing dates in 8 out 26 samples)

Spatial Coverage

Individual & Institutional Roles

Contact(s): Desert Archaeology, Inc.

Prepared By(s): Desert Archaeology, Inc.

Record Identifiers

Technical Report No.(s): 2009-03

Western National Park Association Grant(s): 06-10

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