GIS Use in Open-Air Rock Art Conservation: the Case of the Côa Valley, Portugal

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(1)CAA2010 Fusion of Cultures Proceedings of the 38th Annual Conference on Computer Applications and Quantitative Methods in Archaeology, Granada, Spain, April 2010 Edited by. F. Contreras M. Farjas F. J. Melero. BAR International Series 2494 2013.

(2) Published by Archaeopress Publishers of British Archaeological Reports Gordon House 276 Banbury Road Oxford OX2 7ED England [email protected] www.archaeopress.com. BAR S2494 CAA2010: Fusion of Cultures. Proceedings of the 38th Annual Conference on Computer Applications and Quantitative Methods in Archaeology, Granada, Spain, April 2010 © Archaeopress and the individual authors 2013. ISBN 978 1 4073 1108 1. Printed in England by Information Press, Oxford All BAR titles are available from: Hadrian Books Ltd 122 Banbury Road Oxford OX2 7BP England. www.hadrianbooks.co.uk. The current BAR catalogue with details of all titles in print, prices and means of payment is available free from Hadrian Books or may be downloaded from www.archaeopress.com.

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(602) Proceedings of the 38th Annual Conference on Computer Applications and Quantitative Methods in Archaeology, CAA2010 F. Contreras, M. Farjas and F.J. Melero (eds.). GIS Use in Open-Air Rock Art Conservation: the Case of the Côa Valley, Portugal Fernandes, A.P.B. Côa Park Foundation, Portugal [email protected]. The use of GIS space analysis tools will be examined in reference to the conservation of the Côa Valley rock art. It is proposed that, conservation wise, each outcrop containing rock art is differently affected by slope, aspect and solar radiation. Therefore, the accurate determination of the precise situation of each outcrop regarding the above-men tioned spatial distribution variables will be a valuable aid in the full characterization and assessment of the condi tion of outcrops with rock art. Keywords: Open-air rock art conservation, spatial distribution of rock art, Côa Valley, Portugal. 1. Introduction The Côa Valley Archaeological Park (PAVC, www.artecoa.pt), located in Northern Portugal, possesses an ex traordinary collection of ancient open-air rock art mo tifs. Prehistoric imagery ranges from the Upper Paleo lithic (Figure 1) to the Iron Age, and is located on the banks of the Côa and Douro Rivers and their tributaries (BAPTISTA, 1999). So far, around 40 different rock art sites possessing around 1000 engraved and painted out crops comprising a total of more than 5000 individual motifs were identified (Figure 2). Due to its signific ance, the Côa Valley rock art has been inscribed in the World Heritage List (UNESCO, 1999).. (FERNANDES, 2007). The first stages of research at tempted to holistically understand and characterize the origin and activity of the interconnected weathering dy namics that act upon the rock art outcrops (FERNANDES, 2006). Currently, undergoing research implies the creation of a method to systematically evalu ate the condition of the engraved outcrops, thus priorit izing future conservation work by establishing an ur gency intervention scale (FERNANDES, 2009). Within a total of 1000 rock art outcrops, it is essential to determine which ones are in more urgent need of inter vention. Therefore, the urgency scale is a vital tool to. Since 2000, the author has been developing a Conserva tion Program for the rock art at Côa Valley. Figure 1: Upper Paleolithic representation featuring a two-headed goat in Quinta da Barca rock 1. (Photo: BAPTISTA 1999). Analytical GIS (Short Paper). Figure 2: Location of the Côa Valley rock art sites..

(603) A.P.B. Fernandes / GIS Use in Open-Air Rock Art Conservation: the Case of the Côa Valley, Portugal. Figure 3: Schematic illustration of mechanical instability in the slopes caused by gravitational pressure aided by seis mic forces and rock expansion and retraction cycles.. wards informed conservation, and thus, in extending the ‘life expectancy’ of the rock art outcrops.. Figure 4: Location of Rock 16 from the Vale de José Es teves (16VJE) site.. 2.2. Slope. In order to establish which outcrops are in worse condi tion it was indispensable to identify evaluation paramet ers. Some have to do with geology (rock characteristics namely petrology, porosity, rock strength and so on) others with biology (such as lichen colonization). Once all active parameters were identified it is possible to compare the overall condition and situation of each out crop, thus ranking them regarding the urgency of per forming conservation work. Since there are almost 1000 outcrops that possess rock art motifs, a sample of 40 was chosen. These 40 outcrops will have their condition thoroughly characterized by examining each of the iden tified parameters.. It has been demonstrated that when slope angle in creases, the susceptibility for landslides or rock slope failure also increases (YALCIN et al., 2007; SUMMER FIELD, 1991). Slope dynamics play an important part in outcrop instability. Gravity itself will force different sized elements (from small soil particles to heavier loose rock blocks) to roll downhill which may result to serious damage to the outcrops located below. Furthermore, the hill itself applies great pressure to the outcrops located at its base. The hillsides are in a continuous process of trying to reach a more stable profile (in fact, to have less pronounced slopes). Therefore, the progressive disman tlement of the outcrops located at its base is a part of that process (Figure 3).. 2. Open-air rock art conservation oriented GIS spatial analysis. After calculating the slope for the entire area of study, and for the sites included in the sample (Figure 4), it is possible to accurately ascertain the slope of the hillsides where each engraved outcrop is situated (Figure 5).. Some of the identified parameters have to do with Geo morphology issues. Since the GIS ArcView 9.2 software suite offers a powerful spatial analysis tool, it was de cided to be used to determine aspect, slope, contour and solar radiation. The work base was a 10m resolution DEM of the area of the PAVC, supplied by Instituto Geográfico Português (www.igeo.pt) of which a TIN el evation model can be seen in Figure 2. 2.1. Location of the rock art outcrops Since the precise location of each rock art outcrop in the valley is known, it is possible to determine topographic al situation, namely rise. Using ArcMap statistics tool, it is possible to conclude that more than half are situated in altitudes between 110 and 218 meters, that is, at the foot of sharply inclined hills (see next subsection.). It is also possible to determine average (212 m) and median altitudes (190 m) of the Côa Valley rock art outcrops.. Figure 5: Location (regarding slope) of the rock art sites that have engraved outcrops included in the sample. CAA2010 Fusion of Cultures.

(604) F. Contreras, M. Farjas & F.J. Melero (eds.) / Proceedings of CAA'2010 Fusion of Cultures. 2.3. Aspect YALCIN et al. (2007) review the ways in which aspect can contribute to mass wasting events, all connected with meteorological phenomena: exposition to rainfall, wind and solar radiation. On the other hand, EGLI et al. (2006) have investigated the role of aspect in rock weathering, arriving to the conclusion that there is a marked difference in weathering between south and north facing rock surfaces (greater in north facing sur faces). Again using the DEM it was possible to determine as pect in the area of study. Following YALCIN et al. (2007), aspect was divided in 5 categories: Flat (-1º/0º), North (315º/45º), East (45º/135º), South (135º/225º) and West (225º/315º) (Figure 6). Specific aspect carto graphy of the rock art sites and outcrops in the sample was also produced in a similar fashion, as the maps shown in Figures 4 and 5. 2.4. Solar radiation It is known that rocks undergo expansion and retraction cycles. This behavior can be induced by solar radiation which determines temperature and moisture of any given rock surface (BENNIE et al., 2008).. Figure 7: Average solar radiation affecting 16VJE in 2009.. conclusions regarding the spatial positioning of rock art sites in the Côa Valley. For instance, after calculating the percentage of each aspect class within a rectangular river corridor where the huge majority of rock art sites are located, an even distribution of each class was ap parent with the exception of flat terrain that accounted for only 2.75% (N equaled 24.36%, E 23.33%, S 24.66% and W 24.86%). Previous estimation established that the great majority of all Côa rock art sites have an Eastern aspect (46,8%, against 29,8 for S, 14,9% for W and a mere 8,5% for N). Considering these discrepancies, one main explana tion arises. Differential conservation issues may have determined that less rock art outcrops situated in North facing slopes (thus exposed to harsher conditions) have survived until today but research is still ongoing regard ing this matter. Conclusion. Figure 6: Aspect in the study area with indication of 16VJE, located at the foot of a North facing slope.. Solar radiation was calculated in the area of study with the help of the previously mentioned DEM. It is pos sible, resorting to the raster calculator, to determine the amount of radiation each individual engraved outcrop endures (Figure 7).. 3. Discussion Beyond the primary goal of identifying parameters to distinguish the condition of different outcrops, GIS spa tial analysis has made possible to reach some interesting. Analytical GIS (Short Paper). GIS use in research and management of archaeological remains in general, or rock art sites in particular, is com mon. However, to the best of the author’s knowledge, this is the first time GIS methodologies are being spe cifically used in open-air rock art conservation. GIS spatial analysis within ArcView 9 is a powerful tool to obtain important statistical data, or to create suitable maps and models for illustration purposes (for instance, Figure 8). However, in Archaeology, statistical data and cartography are nothing if not used as an aid to interpret the past, or in facilitating the conservation and preserva tion of significant cultural heritage. The spatial analysis possibilities presented by GIS were essentially used towards the goal of devising methods to identify the conservation state of rock art outcrops. Rise, aspect, slope and solar radiation were the factors con sidered in present research. Preliminary consideration of the first results suggests that there is a clear pattern in the spatial distribution of (surviving) rock art outcrops.

(605) A.P.B. Fernandes / GIS Use in Open-Air Rock Art Conservation: the Case of the Côa Valley, Portugal. in the valley. However this pattern might be explained, the acquired data shows that only when GIS use goes beyond plain, ‘push-button’ solutions, spatial analysis does become a key element in, for instance, the creation of innovative archaeological data interpretation models, deriving pertinent background data useful in understand ing rock art weathering dynamics, or in planning, devis ing and implementing heritage conservation actions.. References BAPTISTA, A. M., 2009. No Tempo Sem Tempo: A Arte dos Caçadores Paleolíticos do Vale do Côa. Parque Arqueológico do Vale do Côa, Vila Nova de Foz Côa. BENNIE, J., HUNTLEY, B., WILTSHIRE, A., HILL, M., BAXTER, R., 2008. Slope, aspect and climate: Spa tially and implicit models of topographic microclimate in chalk grassland. Ecological Modelling, 216, pp. 4759. EGLI, M., MIRABELLA, A., SARTORI, G., ZANEL LI, R., BISCHOF, S., 2006. Effect of North and South exposure on weathering rates and clay mineral formation in Alpine soils. Catena, 67 (3), pp. 155-174. FERNANDES, A. P. B., 2006. Understanding an unique conservation work environment: The case of the Côa Valley rock art outcrops. In Rodrigues, J. D., Mimoso, J. M. (eds.) Theory and Practice in Conservation: A Tribute to Cesare Brandi, pp. 323-332. LNEC, Lisbon.. Figure 8: Location of VJE16 pictured in a 3D elevation model produced with ArcScene.. FERNANDES, A. P. B., 2007. The Conservation Pro gramme of the Côa Valley Archaeological Park: Philo sophy, objectives and action. Conservation and Man agement of Archaeological Sites 9 (2), pp. 71-96. FERNANDES, A. P. B., 2009. Conservation of the Côa Valley rock art outcrops: A question of urgency and pri orities. Antiquity 83 (319). Available from: http://antiquity.ac.uk/projgall/batarda319/. SUMMERFIELD, M., 1991. Global Geomorphology: An Introduction to the Study of Landforms. Longman, Harlow. UNESCO, 1999. Report on the twenty-second session of the World Heritage Commission. Kyoto, Japan. 30 November – 5 December 1998. Available from: http://whc.unesco.org/en/list/866. YALCIN, A., BULUT, F., 2007. Landslide susceptibil ity mapping using GIS and digital photogrammetric techniques: A case study from Ardesen (NE-Turkey). Natural Hazards, 41 (1), pp. 201-22.. CAA2010 Fusion of Cultures.

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