The Use of Lichenometry for Assessment of the Destruction and Reconstruction of Buddhist Sacred Walls in Langtang Valley, Nepal Himalaya, Following the 2015 Gorkha Earthquake

摘要

Mani walls, Buddhist sacred walls constructed of carved blocks, are common in Langtang Valley, Nepal Himalaya. Fieldwork in 2009–2015 documented all 80 mani walls, including all occurrences of the lichen Rhizocarpon geographicum. According to local informants, the mani walls were constructed 400–600 years ago, and the original mani wall was in the village of Ghoratabela. Based on the indirect method, the oldest lichen on a mani wall dated only to 1942, which, within modeling error, was concurrent with the 1934 earthquake, the last major earthquake in Nepal prior to the Gorkha earthquake of 25 April 2015. In November 2015 it was found that 15% of mani walls could not be located and 20% were severely damaged. The original mani wall had apparently been reconstructed 170 m from its previous location. In two severely damaged and three fully intact mani walls, large lichens (12–49 mm) with unhealthy appearance were found that were not previously present. The most likely explanation was that the three intact mani walls had already been reconstructed using previously interior blocks as exterior blocks. This research raises the possibility that many Himalayan religious structures are not the original structures, but are replicates that are reconstructed after natural disasters.