Abstract In the spirit of collaborative research, Glicken and Ford embarked on the problem of identifying the source of volcanic ash used as temper in prehistoric Maya ceramics. Verificiation of the presence of glass shards and associated volcanic mineralogy in thin sections of Maya ceramics was straightforward and pointed to the Guatemala Highland volcanic chain. Considering seasonal wind rose patterns, target volcanoes include those from the area of west and including Guatemala City. Joint field research conducted in 1983 by Glicken and Ford in the limestone lowlands of Belize and neighboring Guatemala, 300 km north of the volcanic zone and 150 km from the nearest identified ash deposits, was unsuccessful in discovering local volcanic ash deposits. The abundance of the ash in common Maya ceramic vessels coupled with the difficulties of long-distance procurement without draft animals lead Glicken to suggest that ashfall into the lowlands would most parsimoniously explain prehistoric procurement; it literally dropped into their hands. A major archaeological problem with this explanation is that the use of volcanic ash occurring over several centuries of the Late Classic Period (c. 600-900 AD). To accept the ashfall hypothesis for ancient Maya volcanic ash procurement, one would have to demonstrate a long span of consistent volcanic activity in the Guatemala Highlands for the last half of the first millenium AD. Should this be documented through careful petrographic, microprobe, and tephrachronological studies, a number of related archaeological phenomena would be explained. In addition, the proposed model of volcanic activity has implications for understanding volcanism and potential volcanic hazards in Central America over a significantly longer time span than the historic period. These avenues are explored and a call for further collaborative research of this interdisciplinary problem is extended in this paper.

In order to support the ashfall hypothesis, three major avenues of evidence need to be pursued: 1) petrographic analysis of Maya ceramics; 2) microprobe analysis of glass shards in the ceramics; and 3) tephra- and geochronological studies in the highlands. The first stage of verification is the petrographic characterization of the volcanic ash in the ancient Maya ceramics of the lowlands. The characterization of the major, minor, and trace elements composition of the volcanic ash together with the phenocryst assemblage could enable one to determine the general volcanic source of the ash. To a large extent, this has been accomplished (Ford and Glicken, 1987). After a review of thousands of ceramic pieces and hundreds of thin section examples of Maya ceramics from major lowland sites, we identified the types of ceramics that had volcanic ash tempering added to the clay paste and determined that volcanic ash made up more than 20% of the ceramic paste matrix of the ash tempered ceramic collections. The ash and assemblage of crystals (biotite, hornblende, hypersthene, and zircon) all are consistent with Guatemala Highland tephra (Drexler et al., 1980; Rose et al., 1981).

Among the biotite-bearing volcanoes, several are known to have been active in the period of 600 to 900 AD. These include El Chichon, Tajamulco, Acatenango, Atitlán, and Cerro Quemado. Cerro Quemado is known to have been quiet active at about 800 AD (Conway et al., 1992) and the area has a complex tephra stratigraphy which suggests that this activity could have continued for some time.

(Ford and Rose, in press)