THE USE OF LICHENOMETRY FOR DATING BUDDHIST SACRED WALLS IN SOLO KHUMBU DISTRICT, NEPAL HIMALAYA

Mani walls, Buddhist sacred walls constructed of carved blocks with Tibetan letters and elaborate imagery, are common throughout the Nepal Himalaya. In a recent study in Langtang Valley, Nepal Himalaya, local informants were interviewed about the mani wall traditions and lichenom­etry was used to resolve discrepancies regarding the maintenance of the mani walls. An apparent growth curve for the lichen Rhizocarpon geographicum was developed using five sources of indirect data, including the foundation of one stupa (sacred monument), two locations of former ice cover, for which ages were obtained from local informants, and two debris ridges that had been dated by Be-10. Based on the growth curve, it was found that the mani walls are cleaned of lichens on a geomet­ric mean cycle time of 13 years. Moreover, by documenting mani walls and their lichens both before and after the earthquake and icefall-debris avalanche of April 2015, it was possible to show that 15% of mani walls could not be located, 20% were severely damaged, and at least four mani walls had been fully reconstructed since the natural disaster. The research in Langtang Valley raised the possibility that (1) many Himalayan religious structures are not the original structures, but are replicates that are reconstructed after natural disasters (2) Himalayan religious structures could be used to date natural disasters. The objective of this study was to carry out the same investigations in Solo Khumbu District, Nepal Himalaya, in order to (1) test the consistency of mani wall maintenance in Nepal Himalaya (2) create a baseline for comparison following a future natural disaster. It was found that R. geographicum did not occur in Solo Khumbu below 4165 m a.s.l. (below the village of Dingboche), in contrast to Langtang Valley where the species was present at 3532 m a.s.l. Sizes of R. geographicum on mani walls ranged from 14.99-73.01 mm, which was equivalent to ages (times since last cleaning) of 4-113 years, using the same growth curve that was developed for Langtang Valley. The geometric mean cycle time of cleaning was 16 years, which was remarkably similar to what was found in Langtang Valley. Some informants claimed that the mani walls were only 40-50 years old, as opposed to the ages of 400-600 years that were given in Langtang Valley. Further results will be reported at the meeting.