Origin of Cinders in Wupatki National Monument

Abstract

Sunset Crater is the youngest cinder cone in a cluster of Quaternary volcanoes at the northeastern edge of the Pliocene to Holocene (5 Ma to Recent) San Francisco Volcanic Field. Based on dendrochronologyspecifically the recovery of complacent tree-rings on several archaeological specimens from Wupatki Ruin-the eruption of Sunset Crater is dated at A.D. 1064 (Smiley 1958). The eruption may have continued episodically for approximately 100 to 200 years (Amos 1986; Champion 1980; Ulrich et al. 1989), although new paleomagnetic data suggests a shorter span, of perhaps 50 years (Duane Champion, personal communication 2001). However, the eight tree-ring samples used for the A.D. 1064 date are of unknown provenance, so it is not known if the complacent rings detected in the samples can, or should, be linked to the Sunset Crater eruption. Ceramic dates from archaeological contexts with and without volcanic ash suggest the eruption occurred between A.D. 1025 and 1150, and most likely in the mid-to-late eleventh century (Boston 1995; Colton 1945; Downum 1988). The eruption of Sunset Crater has played a very important role in Southwest archaeology, particularly in models explaining the dramatic growth in prehistoric settlem ent in the Flagstaff area and Wupatki National Monument in the late eleventh and early twelfth centuries. The earliest and most accepted model suggests that thinly deposited layers of cinder and ash (or tephra) from the eruption acted as a water-retaining mulch that allowed successful farming in areas that were previously too dry (Colton 1932,1946; Downum and Sullivan 1990). Alternative models suggest that large-scale climatic changes and the adoption of different land-use methods had a much more pronounced effect on increasing site density (Pilles 1979).