Casa del Samarín, una estación de grabados rupestres en deterioro. Documentación, análisis y diagnóstico en Los Llanos de Ifara, Granadilla, Tenerife

Abstract

<p class="VARAbstract"><strong>Extended Abstract:</strong></p><p class="VARAbstract">In the archaeology of the Canary Islands (Spain), there are many studies based on the usage of new technologies to contribute to the identification and description of rock art engravings through high-resolution digital models (<a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Mart%C3%ADn_2005">Martín, 2005</a>; <a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Mart%C3%ADn_2007">Martín, Velasco, González &amp; Ramírez, 2007;</a> <a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Senen_2016">Senén &amp; Cuenca, 2016</a>; <a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Navarro_2019">Navarro &amp; Cancel, 2019</a>). This paper is supported by these documentation techniques and digital analysis in order to deepen into the characterization of the damaged rock art station Casa del Samarín (House of Samarín), or Tagoro del Rey, in Los Llanos de Ifara, south of the island of Tenerife (Figs. 1). Twenty-one panels conserved in situ were documented (Fig. 6). Geometric-linear, geometric with an oval and rectangular trend and figurative ones can be distinguished. The blocks <a title="" href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#_ftn1">[1]</a> that compose the engravings station belong to a rocky basalt outcrop, to which other free-standing blocks are attached, forming a circle. The shape that describes this set of blocks is defined as a "cabin" or circular-shaped structure.</p><p class="VARAbstract">This set of engravings, made on a basalt rocky outcrop with a planar factory, show a tendency to suffer from exfoliation and are affected by internal stresses. The intrinsic characteristics of this stone support, together with their exposure to anthropic actions and strong insolation, condition its fragility, with the risk of losing part of the representations that it houses. Given the threat posed by its gradual deterioration, we seek to ensure its digital preservation through precision three-dimensional (3D) records, the engravings inventory, the record of their conservation state and the understanding of the degradation processes that are affecting the outcrop. What has been explained will be addressed quarterly, to observe the evolution of any material changes every three months.</p><p class="VARAbstract">The registration work consisted of taking four photogrammetric surveys in eight months; the surveys were georeferenced by means of a centimetric Global Navigation Satellite System (GNSS) and a total station. Structure from Motion (SfM) technology enabled the researchers to generate high-precision 3D models in an affordable way, not only in terms of cost but also ease of use. Digital copies with Geographic Information System GIS technology were extracted from them, being exportable in shapefile format (Fig. 7).</p><p class="VARAbstract">As regards the documentation of existing pathologies, assuming standardized lexicon and classification criteria (<a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#IPCE_2013">IPCE, 2013</a>), together with a rigorous information systematization, was key for achieving agile handling of the data collected and for facilitating monitoring tasks (Fig. 8). Damage maps were created for collecting the location and scope of the alterations. The complex volumetry of the outcrop and the varied orientation of the panels marked the need to resort to 3D editing so that all their faces could be properly registered (Fig. 10). This project was performed with a 3D design program, Blender®. </p><p class="VARAbstract">Thanks to an imaging analysis process, internal textures of 3D models also provided relevant graphic support for the pictographic content and the conservation state (Figs. 11 &amp; 14). DStretch® (<a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Harman_2008">Harman, 2008</a>), a plugin implemented in the scientific image processing software ImageJTM, was used for this purpose. To conclude, researchers relied on CloudCompare (<a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Girardeau_2015">Girardeau-Montaut, 2015</a>), an advanced 3D data processing software, to tackle a morphometric analysis that allowed us to detect the appearance of formal changes along with the recorded sequences (Figs. 12 &amp; 15). In this process, the distances between two records, taken after six months, were computed with the Cloud to Mesh (C2M) tool, based on the Chamfer distance algorithm (<a href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#Ruiz_2016">Ruiz et al., 2016: 120</a>).</p><p>Registration file cards and damage maps clearly highlighted the main conditions: material losses (shown in orange) and breaks (in green) have affected the outcrop in a generalized way. Furthermore, sedimentary deposits (blue) are concentrated in interstices; while lichen colonies (idem) do so in the least sun-exposed areas. The use of DStretch® highlighted modern excoriations of anthropogenic origin and contributed to distinguishing recent material losses from the older ones, already affected by an incipient patina. Finally, thanks to morphological analysis, a new detachment (Fig. 15b) and a generalized displacement of exempt elements (Figs. 12 &amp; 15) were detected. These displacements indicate outstanding manipulation, which could lead to decontextualizations or new fragmentations.</p><p>Regarding the archaeological interpretation, macroscopic observation of exempt blocks located in the vicinity of the station and the zenith representation of the immediate environment from photogrammetry, have shown that they are forming a set of attached structures (Fig. 13). The site redefinition and the diagnosis of its very weakened defensive system show the need to intensify the archaeological study of this area, so emblematic for the archaeology of the south of Tenerife, in addition to establishing preventive conservation measures that can contribute to its stabilization.</p><p class="VARAbstract"> </p><div><hr align="left" size="1" width="33%" /><div><p><a title="" href="file:///L:/PC%20Port%C3%A1til%20Poli/Mis%20documentos/VAR/En%20Curso/Revisi%C3%B3n/13810/13810-60985-2-CE_jll.docx#_ftnref1">[1]</a> Geological unit of size greater than 300 mm, term standardized by the USCS (Unified Soil Classification System).</p></div></div>