The Source of Volcanic Ash In Late Classic Maya Pottery at El Pilar Belize and Guatemala

The appearance of volcanic ash in Late Classic (AD 600-900) Maya pottery is well documented in archaeological literature. The majority of archaeological studies have focused primarily on mineralogical composition through the use of the polarized light microscope. The purpose of this study is to surpass previous investigation to find the source of the volcanic ash using geologic techniques. Thin sections of Late Classic Maya ceramics containing ash from El Pilar, Belize, were made and basic mineralogy was identified. The volcanic ash within the Maya thin sections was analyzed using the microprobe to determine major element composition. The volcanic ash was found to be rhyolitic with an SiO₂ concentration of 78% wt. Potential source volcanoes in Mexico and Central America were located based on prevailing wind patterns, average wt % SiO₂, and eruption volumes. Geochemical data was obtained from possible volcanic sources for comparison to the Maya ash. El Chichon was chosen for analysis first as ash from the 1982 eruption fell at El Pilar. The Maya ceramics thin sections were sent out for IPC-MS to determine concentrations of trace elements and lead isotopes. Results were compared to data from El Chichon volcano and it was found that geochemical data did not support El Chichon as the volcanic source. Data from the Maya ceramics is now being compared to other potential source volcanoes in this same way. The other avenue that is being explored at present is the alteration of the volcanic ash due to the firing process. Experiments were done where Maya clay and volcanic ash from the Bishop tuff were mixed and made into briquettes and then fired at controlled temperatures and times. Analysis of the volcanic ash pre and post firing shows that alteration occurs to both major and trace elements due to low temperature ceramic firing.