Introduction

Mani walls, Buddhist sacred walls constructed of carved blocks with Tibetan letters and elaborate imagery, are common above Ghoratabela in Langtang Valley (Nepal Himalaya), and especially between the site of the former Langtang Village and Kyanjin Gompa (Figs. 1–5). Although mani walls are prominent features of the landscape in the Bhutan, India, and Nepal Himalaya, were described by early traveling scholars in the Himalaya (Pranavananda, 1939; Hamond, 1942), and are widely photographed in the tourist literature, the scholarly literature on mani walls is still amazingly sparse. Recently, Ardussi (2004, 2007) produced the first translations and interpretations of the carved inscriptions on a mani wall in Bhutan.The geologic interest in mani walls was awakened by the suggestions of Weidinger (2001a, 2002) that the mani walls were constructed as landslide warnings, which is consistent with their location and alignment downslope of and parallel to the distal edges of prominent landslides. Stolle et al. (2015) found that two-thirds of the mani walls in their study area in the Trans-Himalayan Ladakh and Zanskar Ranges (northwestern India) were oriented perpendicular to river channels. Moreover, during the catastrophic debris flows of August 2010, many of these mani walls acted as local flow barriers that deflected and diverted the debris flows.

Bunds et al. (2010) and Emerman et al. (2016) began a program of lichenometry in Langtang Valley with the objective of dating GLOF (glacial lake outburst flood) deposits. Because lichen growth rates are variable, it is necessary to calibrate lichen growth rate of a selected lichen species for each study locality by measuring the growth rates of individual lichens over a period of years (called the direct method) or by measuring the maximum (or other statistical measure) of lichen diameters on surfaces for which age is known from independent evidence (called the indirect method) (Innes, 1988). Gravestones have often been used as surfaces of known age.There have been only a handful of lichenometric studies in the Himalaya, partly due to the lack of gravestones that can be used for calibration. Although it may be possible to calibrate lichen growth rates based on the British cemeteries in the Hill Stations of the Indian Himalaya, this approach has not yet been pursued. Vohra (1981) and Srivastava et al. (1995) mentioned lichenometric studies on moraines of the Gara and Gor-Garang Glaciers in the India Himalaya, but did not present the results. Sah (1995) discussed the prospects for lichenometry in the Himalaya. Srivastava et al. (2004) and Awasthi et al. (2004) used lichens to date the moraines of Gangotri Glacier in the India Himalaya. In those studies, lichen growth was calibrated by measuring lichens on boulders of two moraines whose ages were known from prior fieldwork early in the 20th century. Gupta (2005) carried out relative dating of portions of a major landslide in Himachal Pradesh (India Himalaya) using percent lichen cover without regard to lichen species. Ibetsberger (2005) measured the diameters of Rhizocarpon geographicum on moraine boulders in Langtang Valley (Nepal Himalaya). Since there was no local calibration of growth rates, the interpretation was only qualitative and was used to distinguish between Holocene and Little Ice Age moraines. Chaujar (2006) calibrated the growth of R. geographicum at four sites in Himachal Pradesh using dated monuments. Most recently, Chaujar (2009) calibrated the growth of R. geographicum in the Garhwal Himalaya by monitoring the diameters of seven lichens over a fouryear period and using the absence of R. geographicum on a dated bridge to establish a minimum time for initial colonization of the surfaces by lichen (called the colonization delay). Chaujar (2009) used the results to date the moraines of the Chorabari Glacier. Yang et al. (2008) has used the maximum diameter of R. geographicum growing on a fan formed by a GLOF of known age to date moraines on the Tibetan Plateau. We are not aware of any lichenometry that has been carried out anywhere in the Bhutan, Nepal, or Pakistan Himalaya aside from Ibetsberger (2005), Bunds et al. (2010), Carlson et al. (2012), and Emerman et al. (2016). Even the description of lichens in Nepal could be regarded as in its infancy. R.geographicum, which was used in this study, was not reported by Sato (1962),Awasthi (1988, 1991), or Sharma (1999), but was mentioned by Miehe (1990) and Bamya et al. (2010). Recently, Olley (2008) reported on a lichen-collecting expedition to the Langtang Himalaya and Olley and Sharma (2013) produced a preliminary list of species.

FIGURE 1.

Buddhist sacred walls, called mani walls, are common in Langtang Valley (Nepal Himalaya) and especially between the site of the former Langtang Village and Kyanjin Gompa.This mani wall is adjacent to the monastery in Kyanjin Gompa (mani wall no. 80 in Table 1b). The mani wall suffered no apparent damage from the 2015 Gorkha earthquake, although the monastery was heavily damaged.

FIGURE 2.

Many of the mani wall blocks include carved text in Tibetan letters (mani wall no. 80 in Table 1b, Fig. 1). According to local informants, the Tibetan writing does not state the dates of construction or cleaning of the mani walls. Note that the apparent jagged edges of the block are simply shadows.

FIGURE 3.

Many of the mani wall blocks include carved imagery (mani wall no. 80 in Table 1b, Fig. 1). Note that the apparent jagged edges of the block are simply shadows.

FIGURE 4.

The 2015 Gorkha earthquake caused massive landsliding in Langtang Valley, resulting in loss of life and the destruction of villages and cultural artifacts.

FIGURE 5.

Out of 80 mapped mani walls in Langtang Valley, 12 (15%) were completely destroyed and 16 (20%) were severely damaged. The remainder suffered no apparent damage, although there was evidence that at least four had been rebuilt.

It was hoped that the inscriptions on the blocks of the mani walls (Fig. 2) would date the mani walls and act as the independent evidence required by the indirect method. However, it became apparent from interviews with local informants that the inscriptions, in fact, did not date the mani walls. On the other hand, some of those same informants were able to identify and provide dates for two positions of former ice cover and for a stupa (sacred monument) in the vicinity of Kyanjin Gompa (Figs. 4–5). In the same vicinity, Barnard et al. (2006) had carried out ¹⁰ Be dating of two debris ridges.The maximum diameters of R. geographicum were measured on boulders at the four geologic sites and on the carved blocks of the foundation of the stupa in 2009 and 2014, and were used to construct an apparent lichen growth curve for use by the indirect method of lichenometry (Bunds et al., 2010; Emerman et al., 2016). In addition, lichen diameters measured on 20 boulders in 2009 and 2014 were used to compare the results of the direct and indirect methods (Emerman et al., 2016). An earlier version of the apparent growth curve that did not include the stupa was used by Carlson et al. (2012) to date terrace evolution and incision rates along the uppermost Langtang River.

Since the mani walls could not be dated by their inscriptions and since an apparent lichen growth curve was developed from other geologic and cultural features of known age, the objective of the research program changed to using the lichens on the mani walls to date the mani walls themselves. Benedict (2009) has reviewed the application of lichenometry to archaeology, and Winchester (1988) also used lichenometry to date stone monuments. Fieldwork in 2009,2011, and 2014 involved mapping and photographing all mani walls in Langtang Valley, measuring and photographing all occurrences of the lichen R. geographicum on the mani walls, and interviewing local informants regarding the history and traditions of the mani walls.The local informants agreed or did not disagree regarding the following:

However, there was considerable disagreement as to whether the mani wall blocks have ever been re-cut and whether, when, and how the mani walls (besides the mani wall near Ghoratabela) are cleaned, especially as to whether they are cleaned with an iron brush that would remove crustose lichens (Emerman et al., 2016). From this standpoint, the age of a mani wall, as determined by lichenometry, can be regarded as the time since the mani wall was last cleaned of R. geographicum, which would represent the most intense level of cleaning with an iron brush.

Using the apparent growth curve, Emerman et al. (2016) found the geometric mean age (time since last cleaning) of the mani walls to be 13 years with geometric standard deviation range of 4–38 years. The best estimate for the earliest date of thorough cleaning of any individual mani wall was 1942. Out of the 12 lichens on mani walls that were measured in 2009 and re-measured in 2014, five had decreased in size. Moreover, three lichens measured in 2009 had disappeared by 2014. Based on the above results, Emerman et al. (2016) concluded that it is very likely that the mani walls in Langtang Valley are occasionally thoroughly cleaned to the extent that the crustose lichen R. geographicum is removed. Further evidence for cleaning of the mani walls was the appearance of the mani wall near Ghoratabela (Figs. 4–5), which the majority of informants called the original mani wall, which was never cleaned. In contrast to every other observed mani wall in Langtang Valley, this mani wall was almost entirely covered by mosses and surrounded by many fallen blocks, which is consistent with several centuries of lack of maintenance (Emerman et al., 2016). To the best knowledge of the author, the study of Emerman et al. (2016) was the first use of lichenometry to resolve discrepancies in oral histories. The discrepancies could be further investigated by comparing lichen sizes (reflecting time since last cleaning) with relative amounts of rock weathering (reflecting time since last cutting). However, any investigation of sacred objects would need to be carried out in a non-destructive manner.

On 25 April 2015, Nepal was struck by an earthquake of moment magnitude 7.8 with epicenter 21 km NNE of the city of Gorkha (Fig. 4; Collins and Jibson, 2015; Kargel at al., 2015). The death toll of ~9000 was accompanied by massive destruction of the temples, monuments, and other religious and cultural heritage of Kathmandu Valley (Hossain et al., 2015). An icefalldebris avalanche triggered by the Gorkha earthquake completely buried Langtang Village, killing at least 350 people (Figs. 4–5; Fukuoka and Bhandary, 2015; Miehe and Weidinger, 2015; Lacroix, 2016). The avalanche accumulated 6.95 × 10⁶ m³ of deposits in the valley with thicknesses up to 60 m, and an additional 9.66 × 10⁶ m³ on the glaciated slopes above 5000 m a.s.l. (Lacroix, 2016). On 12 May 2015, Nepal was struck by another earthquake of moment magnitude 7.3 with epicenter 21 km SW of Kodari (Fig. 4; Collins and Jibson, 2015; Kargel at al., 2015).The second earthquake caused 157 more fatalities in Nepal, India, and Tibet, but only relatively minor additional landsliding in Langtang Valley (Hossain et al., 2015; Kargel et al., 2015).

After learning of the tragedy in Langtang Valley, it occurred to the author that the date of the earliest mani wall was, within modeling error, concurrent with the 1934 earthquake, the last major earthquake (moment magnitude = 8.0) to strike Nepal prior to the 2015 Gorkha earthquake (Hossain et al., 2015). (The error in lichen ages was almost entirely due to the misfit of the five data points to a power-law curve, as opposed to the error in measuring individual lichens [Emerman et al., 2016].) The concurrence of dates led to the following questions:

The latter question is related to the new field of archaeoseismology, in which damage to archaeological sites is being used to date earthquakes, thus far, mostly in the Mediterranean and Near East (Sintubin et al., 2009; Niemi et al., 2013).

The objective of this study was to repeat all fieldwork in Langtang Valley, including mapping and photographing mani walls, measuring the lichens on mani walls, and interviewing the local residents, in order to assess the destruction and possible reconstruction of the mani walls following the 2015 Gorkha earthquake. In contrast to the previous paper that reported on only the mani walls that hosted lichens (Emerman et al., 2016), this paper reports on all mani walls in Langtang Valley and, thus, is the first systematic compilation of mani walls for any part of the Himalaya. This study has built upon the impressive body of work carried out on the geomorphology and hydrology of the Langtang Valley since the 1980s, including, in addition to previously cited work, Heuberger et al. (1984), Ono (1985,1986), Fukushima et al. (1987), Shiraiwa et al. (1990), Shiraiwa and Watanabe (1991), Watanabe (1994, 1998),Weidinger and Schramm (1995), Weidinger et al. (1996,2002), Bäumler et al. (1996,1997), Heuberger and Ibetsberger (1998), Schramm et al. (1998), Watanabe et al. (1998), Weidinger (1997, 1998, 2001b), Abramowski (2004), Ibetsberger and Weidinger (2004), Takagi et al. (2007), Owen et al. (2008), Kemp et al. (2012), Nuimura et al. (2012), Miles et al. (2016), and Wilson et al. (2016).

Materials and Methods

All post-earthquake fieldwork was carried out from 18 to 25 November 2015, almost exactly six months after the earthquake. All field measurements were made without reference to previous notes to avoid any biasing of measurements or documentation. Additional interviews with local residents did not follow a fixed set of questions, but concerned the history and traditions of the mani walls, the maintenance and cleaning of the mani walls, the damage caused by the 2015 earthquake, and any previous damage to the mani walls (Appendices A-F). With the exception of the last interview, which was carried out in English (Appendix F), all interviews were conducted in Tibetan, and were translated by Lhakpa Tsering Sherpa, who was fluent in both English and Tibetan. The Tibetan writing on the mani walls could not be read by any of the informants, the author, or the translator.

Damage to mani walls was assessed in the four categories (1) none, (2) slight, (3) severe, and (4) destroyed. No damage meant that no blocks were apparently out of place. Slight damage meant that one or more blocks had slipped out of place, but it was fairly obvious how to reconstruct the mani wall. Severe damage meant that so many blocks had fallen that it was not clear to a layman how to reconstruct the mani wall (Figs. 6–7). A mani wall was classified as destroyed if it could not be located at all. The location of each mani wall was measured in the middle of the mani wall using the Garmin eTrex 10 GPS Receiver. There are minor discrepancies with the locations reported by Emerman et al. (2016) since those studies reported the location at the position of the largest lichen on each mani wall.

This study followed the same lichen measurement procedures as Emerman et al. (2016). Lichens that met the description of Purvis et al. (1992) and St. Clair (1999) were assigned to Rhizocarpon geographicum, the most common lichen used for lichenometric dating (Bradwell and Armstrong, 2007).These lichens may have included species of similar appearance within Rhizocarpon subgenus Rhizocarpon, but precise identification to the species level was unrealistic in the current absence of a Rhizocarpon taxonomy for the Himalaya. Even when taxonomies have been developed, the lumping of species of similar appearance into R. geographicum (sometimes referred to as R. geographicum agg.) is a common practice in lichenometry (Benedict, 1988, 2009). (Since no other lichens were studied, R. geographicum and “lichen” are used interchangeably throughout the remainder of this paper.)

FIGURE 6.

Mani wall no. 60 (Table 1d) was classified as “severely damaged” because it was not obvious how to reassemble the fallen blocks. Although the largest lichen found in 2014 was 22.91 mm, no lichens were found in 2015. Most likely, the earthquake damage buried the block that hosted the lichen.

Care was taken to measure thalli only of individuals, as opposed to composites that form when two or more individuals grow together. Discrimination between individual and composite thalli used the following criteria: approximate circular to smoothly elliptical shape (Ellis et al. 1981; Proctor, 1983), sharp margins, well defined hypothallus, and homogeneity of color and texture within the thallus. In addition, the presence of numerous much smaller thalli in close proximity to each other around an anomalously large thallus was considered sufficient evidence that the large thallus may be composite and such thalli were not measured. The single lichen with the largest diametrical axis (including the hypothallus) on each mani wall was measured six times with a digital calipers with graduation of 0.01 mm. The major source of measurement error was the difficulty in repeatedly placing the calipers in the same position on a rough rock surface. The standard error of the mean of each lichen size averaged over all lichens in this study was ±0.16 mm. As in previous fieldwork, all occurrences of R. geographicum on mani walls were photographed, although only the largest lichen was measured.

FIGURE 7.

Mani wall no. 64 (Table 1f) was classified as “severely damaged” because it was not obvious how to reassemble the fallen blocks.The largest lichen found in 2015 (49.05 mm) was much larger than the largest lichen found in 2014 (22.82 mm) and was not the same lichen. Most likely, the earthquake damage exposed a larger lichen on an interior block.

Results

Additional interviews did not change the four areas of general agreement among the informants that were listed in the Introduction (Appendices A-F). However, one of the informants (Appendix F) said that the structure at Ghoratabela (Figs. 4–5) that was referred to as the original mani wall by other informants was not a mani wall at all, but a chorten (a word used to describe conical-shaped sacred monuments in this region). Based on appearance, the word choice of the informant (Appendix F) seems reasonable by comparing other structures that other informants described as chortens (Fig. 8, parts a and b),the structures that informants described as mani walls (Fig. 1), and the structures that other informants described as the original mani wall (Fig. 9, parts a and b). On the other hand, the structure at Ghoratabela had been described as the original mani wall by the lay lama at the monastery in Kyanjin Gompa in addition to other informants (Emerman et al., 2016). The distinction is not simply a matter of vocabulary, but a question as to whether the structure at Ghoratabela serves as an artistic ancestor to the other mani walls. For completeness and because there was disagreement, the structure at Ghoratabela is included in the list of mani walls (mani walls nos. 4–5 in Table 1a; see further discussion below).

FIGURE 8.

(a) Mani wall no. 77 (Table 1d) was mapped in 2009 and 2014, but could not be located in 2015. In its place stood a conical structure (called a chorten) that had been apparently constructed out of the scattered blocks, (b) This is a close-up of Figure 8, part a. The broken block with carved Tibetan letters on the top of the chorten was probably a remnant of mani wall no. 77 (Table 1d).

On the other hand, additional interviews showed the same disagreement as in previous fieldwork (Emerman et al., 2016) regarding whether the mani wall blocks have ever been re-cut and whether, when, and how the mani walls are cleaned, especially as to whether they are cleaned with an iron brush that would remove crustose lichens (Appendices A-F). The range of disagreement in this study was even greater since one of the informants (Appendix B) stated that the original mani wall at Ghoratabela had been cleaned in the past with a brush and chisel, and that even the lichens had been cleaned off. There was also a range of disagreement as to whether the mani walls had ever been damaged or repaired in the past. The oldest informant would have been born in 1935 (Appendix C), so that no informants would have had a personal memory of the 1934 earthquake (but see discussion of memories from ancestors in the Discussion).

FIGURE 9.

(a) The appearance of mani wall no. 4 (Table 1a) near Ghoratabela, as seen in 2014, was consistent with the oral tradition that this was the original mani wall (constructed 400–600 years ago) and had never been cleaned, (b) Mani wall no. 4 (Fig. 9, part a; Table 1a) could not be located in 2015. However, mani wall no. 5 (Table 1a) with a similar appearance was found in 2015 and was also referred to as the original mani wall.

Out of the 80 mani walls in Langtang Valley, it was found that 12 mani walls (15%) were completely destroyed and 16 mani walls (20%) were severely damaged (Figs. 5–7, Tables 1a–1f). It is certain that the damage was caused by the Gorkha earthquake and the resulting landslide and airblast (Kargel et al., 2015), since no damaged mani walls were seen during any previous fieldwork. The 12 destroyed mani walls included the five mani walls that had previously been present in Langtang Village and which were completely buried by the landslide (mani wall nos. 9–13,Table 1a). At the sites of the remaining seven destroyed by landslides, nothing could be seen that resembled a mani wall. However, at each of three sites of former mani walls (mani wall nos. 67, 76, and 77,Table 1d), a chorten was found that was topped by what was apparently a broken, carved block of a former mani wall (Fig. 8, parts a and b). This combination of a chorten topped by a mani wall block had never been seen by the author before anywhere in the Nepal Himalaya and could be regarded as a form of post-disaster religious art. It is important to note that there were no cases of slightly damaged mani walls and no transition zones between areas of undamaged and either severely damaged or destroyed mani walls (Fig. 5). It is most likely that the mani walls had already been repaired in cases where it was obvious how to put the blocks back into place.

The original mani wall in Ghoratabela could not be found among the scattered boulders and fallen trees at the location where it had been previously mapped (mani wall no. 4 in Table 1a, Figs. 5, 9, part a). However, a similar structure that had not existed prior to the 2015 Gorkha earthquake was found 170 m to the northeast of the previous original mani wall and closer to the trail that passes through Ghoratabela (mani wall no. 5 in Table 1a, Figs. 9, part b, and 10). The structure shown in Figure 9, part b, could be regarded as a postearthquake memorial structure similar to the chortens shown in Figure 8, parts a and b. However, the structure shown in Figure 9, part b, was repeatedly referred to as the original mani wall by one of the informants (Appendix B) during an interview that took place within site of the structure. The most likely interpretation is that the original mani wall had been rebuilt in a more convenient location. The easiest mani wall to replicate would be a mani wall that looked as if it had received no maintenance for several centuries (Fig. 9, parts a and b), as opposed to replicating the intricate design of the maintained mani walls (Fig. 1). Note that the list of 80 mani walls counts the two original mani walls as separate mani walls (mani wall nos. 4–5 in Table 1a).

All 80 mani walls were placed into six categories depending upon the nature of the occurrence of R. geographicum on the mani walls:

The six tables have a common numbering system that numbers all mani walls from west to east. Note that this differs from the numbering system of Emerman et al. (2016), which included only mani walls with R. geographicum.

In all cases in which there was either an increase or decrease in the size of the largest R. geographicum between 2014 and 2015 (Tables 1b and 1c), comparison of photographs verified that the same lichen was measured in both years. The geometric mean growth rate of 0.64 (0.34– 1.21) mm yr^-1 (Table 1b) was similar to the geometric mean growth rate of 0.47 (0.27–2.76) mm yr^-1 that was obtained by Emerman et al. (2016) using the direct method. (The lower and upper range is the geometric mean divided by and multiplied by the geometric standard deviation, respectively. The use of geometric means was justified in Emerman et al. [2016].) There were four mani walls on which the largest lichen decreased in size during the 18-month period from 2014 to 2015, three on undamaged mani walls, and one on a severely damaged mani wall (Table 1c). By comparison, during the fiveyear period from 2009 to 2014, lichens decreased in size on five mani walls (Emerman et al., 2016). A decrease in size of an individual lichen is mostly likely due to cleaning with an iron brush without a commitment to completely remove a crustose lichen during each cleaning episode (Emerman et al., 2016). In that case, there seems to have been extra attention paid to the partial scrubbing of crustose lichens during the post-earthquake period. The geometric mean removal rate per lichen was 1.88 (0.48–7.36) mm yr^-1 from 2014 to 2015, which was comparable to the geometric mean removal rate per lichen of 0.99 (0.35–2.80) mm yr^-1 from 2009 to 2014.

There were eight mani walls on which R. geographicum was present in 2014, but on which R. geographicum could not be found in 2015 (Fig. 6, Table 1d). Four of these cases are probably irrelevant as the mani walls themselves could not be located (Table 1d). Two of the mani walls were severely damaged so that the block that hosted the lichen was most likely buried by other blocks, leaving two undamaged walls on which formerly present R.geographicum was no longer present (Table 1d). By contrast, three mani walls had the crustose lichen completely removed between 2009 and 2014 (Emerman et al., 2016), which again suggests extra attention to the cleaning of mani walls during the post-earthquake period. Of those three mani walls, which still had no lichens in 2015, two were destroyed and one was severely damaged (Table 1e).

TABLE 1a

Catalog of mani walls in Langtang Valley, 2009–2015. Absence of Rhizocarpon geographicum.

Continued

TABLE 1b

Catalog of mani walls in Langtang Valley, 2009–2015. Growth of Rhizocarpon geographicum from 2014 to 2015.

TABLE 1c

Catalog of Mani Walls in Langtang Valley, 2009–2015. Decrease in size of Rhizocarpon geographicum from 2014 to 2015.

Continued

TABLE 1d

Catalog of mani walls in Langtang Valley, 2009–2015. Rhizocarpon geographicum present in 2014 but missing in 2015.

TABLE 1e

Catalog of mani walls in Langtang Valley, 2009–2015. Rhizoarpon geographicum present in 2009 but missing in 2014 and 2015.

TABLE 1f

Catalog of mani walls in Langtang Valley, 2009–2015. Largest Rhizocarpon geographicum in 2015 not present in 2009 or 2014.

The most challenging observation is the existence of five mani walls on which the largest R. geographicum in 2015 was not even present during any previous fieldwork (Table 1f, Figs. 7, 11–13). In one case, there was a lichen present in 2014, but it was much smaller (22.82 mm) than the lichen present in 2015 (49.05 mm) and, by a comparison of photographs, was not the same lichen (mani wall no. 64 in Table 1f, Fig. 7). In the other four cases, no lichens at all were present in 2014, and even the smallest previously unseen lichen was too large (11.59 mm) to have colonized the mani wall and grown to its measured size over an 18-month period.Two of the mani walls were severely damaged, but the other three appeared to have suffered no damage at all (Table 1f, Figs. 7, 11–13). The challenging question is: Where did these previously unseen lichens and the mani wall blocks that hosted them come from? In previous fieldwork, no mani wall blocks were seen that were not part of a mani wall and there were no suggestions from any of the informants that any unattached mani wall blocks existed. Moreover, any freshly carved mani wall block would have hosted lichens no larger than a few millimeters.

The only plausible explanation for the post-earthquake appearance of previously unseen lichens is that mani wall blocks that were formerly interior blocks were present on the exterior. All of the previously unseen lichens were heavily bleached with a strong color contrast from white to pale yellow (Fig. 14), as opposed to the bright yellowish-green of healthy R. geographicum (Purvis et al., 1992; St. Clair, 1999).These lichen colors were consistent with a previous history as an interior block, where only diffuse light with a strong spatial heterogeneity of light intensity would be present. (Note the open spaces that would allow some light penetration in the apparently undamaged mani walls [Figs. 1, 11–13].) These previously interior blocks were present on the exterior either because the mani wall had been severely damaged (mani wall nos. 48 and 64 in Table 1f, Fig. 7) or because the mani walls had been severely damaged and then rebuilt in a way that was not an exact replication of the previous design (mani walls nos. 44 and 53–54 in Table 1f, Figs. 11–13). The three apparently reconstructed mani walls were all within 195 m of one another in the village of Mundu (note the houses in the background of Figs. 11 and 13).At the time of the fieldwork, aside from yak herders living in temporary dwellings above Ghoratabela (Appendix B), Mundu was the only inhabited village in Langtang Valley between Rimche and Kyanjin Gompa (Fig. 5), as all other villages were heavily damaged and still abandoned. It seems reasonable that an inhabited village would be one of the first places where mani walls would be reconstructed.

Discussion

There are five lines of evidence that, within six months of the 2015 Gorkha earthquake, at least four mani walls had been reconstructed in a manner similar to, but not identical to, the original designs:

FIGURE 10.

The original mani wall was apparently rebuilt 170 m to the northeast and closer to the trail that passes through Ghoratabela. The background aerial photo is a Google Earth image dated 8 November 2014 (before the 2015 Gorkha earthquake). In November 2015 all buildings in Ghoratabela were still heavily damaged and there were no residents.

FIGURE 11.

Although mani wall no. 53 (Table 1f) had no apparent damage, the largest lichen in 2015 was 43.42 mm, although no lichens were present in 2009 or 2014. The most likely explanation is that the mani wall had already been reconstructed in such a way that a formerly interior block was placed on the exterior of the mani wall. The mani wall was in the village of Mundu (Fig. 5), which was inhabited at the time of the 2015 fieldwork (note house in background).

FIGURE 12.

Although mani wall no. 54 (Table 1f) had no apparent damage, the largest lichen in 2015 was 37.80 mm, although no lichens were present in 2009 or 2014. The most likely explanation is that the mani wall had already been reconstructed in such a way that a formerly interior block was placed on the exterior of the mani wall. The mani wall was in the village of Mundu (Fig. 5), which was inhabited at the time of the 2015 fieldwork. Mani wall no. 54 is only 9 m east of mani wall no. 53 (Fig. 11).

FIGURE 13.

Although mani wall no. 44 (Table 1f) had no apparent damage, the largest lichen in 2015 was 38.28 mm, although no lichens were present in 2009 or 2014.The most likely explanation is that the mani wall had already been reconstructed in such a way that a formerly interior block was placed on the exterior of the mani wall. The mani wall was in the village of Mundu (Fig. 5), which was inhabited at the time of the 2015 fieldwork (note house in background).The three reconstmcted mani walls (nos. 44, 53, 54) are within 195 m of one another.

The last two observations would not constitute evidence for reconstruction by themselves, but they help to support a pattern of extra attention paid to the mani walls after the earthquake. It should be emphasized that the count of four reconstructed mani walls is an absolute minimum. Any apparently undamaged mani wall could have been reconstructed with no evidence as long as there were no previously unseen lichens and the mani walls had been reconstructed in a manner indistinguishable from the previous design, for a total of 47 possible reconstructed mani walls.

FIGURE 14.

The lichens found on mani wall no. 54 (Fig. 12) were heavily bleached with a strong color contrast from white to pale yellow, as opposed to the bright yellowish-green of healthy Rhizocarpon geographicum. The lichen colors were consistent with a previous history as an interior block, where only diffuse light with a strong spatial heterogeneity of light intensity would be present.

There are three lines of evidence that reconstruction of mani walls may have occurred after the previous major earthquake in 1934.

It is now appropriate to reconsider the hypotheses mentioned previously, namely, the hypothesis of Weidinger (2001a, 2002) that the mani walls were constructed as landslide warnings, and the hypotheses of this study that many Himalayan religious structures are not the original structures, but are replicates that are reconstructed after natural disasters, and that Himalayan religious structures could be used to date natural disasters. The locations of mani walls are not necessarily the sites of actual landslide danger, but are the sites of the local perception of landslide danger at the time of construction. Both the reality and the perception of landslide danger could change with time due to, for example, glacial retreat. On that basis, a fascinating exercise would be comparing a mani wall map (Fig. 5) with the various models regarding the evolving geomorphology of Langtang Valley over the past few centuries (Ono, 1985, 1986; Shiraiwa et al., 1990; Shiraiwa and Watanabe, 1991; Bäumler et al., 1996, 1997; Heuberger and Ibetsberger, 1998;Watanabe, 1998; Ibetsberger and Weidinger, 2004; Ibetsberger, 2005; Barnard et al., 2006; Bunds et al., 2010).

The hypothesis that many Himalayan religious structures are reconstructions has been strengthened and may be helpful in the emerging field of scientific study of ancient Himalayan religious structures (Bhatnagar and Singh, 2003). Moreover, the hypothesis may lead to a new context and set of questions for Himalayan oral history. For example, according to recent fieldwork in the Solo Khumbu District of Nepal Himalaya, many informants stated that the mani walls were only 40–50 years old, which were much younger than the ages reported in Langtang Valley (Goldsberry et al., 2016). The last hypothesis that Himalayan religious structures could be used to date natural disasters is probably not yet realistic until there is an improvement in the precision of lichenometry or some other method. For the same reason, the use of lichenometry for relating the GLOF and glacial cycles in Langtang Valley has not yet been successful (Bunds et al., 2010; Emerman et al., 2016).

Conclusions

This study has used lichenometry, as well as location and photographic records, to show that at least four mani walls in Langtang Valley, Nepal Himalaya, had been reconstructed within six months of a major earthquake and landslide that completely destroyed 15% of the mani walls and severely damaged another 20%. These reconstructed mani walls included the original mani wall at Ghoratabela and three mani walls in the inhabited village of Mundu.The reconstructed mani walls did not follow exactly the same design as the previous mani walls and, in the case of the original mani wall, the reconstructed mani wall was not in the same location. In terms of understanding the cultural and geological significance of the mani walls, it would be very worthwhile to document the continued reconstruction of the mani walls through time. However, regardless of what happens in the future, it is important to note that, with all of the pressing needs in the months following the tragedy of 25 April 2015, and the preparations for the winter of 2015–2016, the residents of Langtang Valley did not delay in the reconstruction of the religious and cultural heritage of the valley.