84 Geoclimbing at La Pedriza del Manzanares (Madrid, Spain). Natural and anthropogenic weathering processes García-Rodríguez M. 1,* , Fernández-Escalante E. 2 1 Universidad Nacional de Educación a Distancia (UNED). Esparta Avenue, s/n. 28232 Las Rozas-Madrid, Spain. *corresponding author email: 2 Tragsa R&D, 58 th Maldonado Street, 28006, Madrid, Spain *Corresponding author: manu.garo@ccia.uned.es Introduction La Pedriza del Manzanares (Madrid, Spain) is one of the most important granitic landscapes in Europe. Its geomorphological worth poses a global reference to the study of granite reliefs. Additionally, it functions as a natural laboratory for examining physical and chemical weathering processes. This geomorphological weald entails a high value from a scenic and sporting point of view, particularly for climbing [1]. La Pedriza del Manzanares is the main climbing school in the Madrid region. It is listed as a Site of Geological Interest (LIG) in nearly all existing inventories and was declared a Natural Site of National Interest in 1930. In 1978 it became part of the Cuenca Alta del Manzanares Natural Park, reclassified as a Regional Park in 1985. In the 1990s it became a UNESCO Biosphere Reserve. In 2013, the creation of the Sierra de Guadarrama National Park, which included La Pedriza del Manzanares, was approved. This article is within the framework of the UNESCO International Project IGCP 714 - 3GEO: Geo-Geoclimbing & Geotrekking in Geoparks, which aims to promote the dissemination of geosciences [2,3]. Climbing in natural environments is a sporting activity of great interest for understanding the forms and processes that shape rocks. The weathering processes observed on rock slabs vary based on their orientation, allowing us to identify distinct patterns and characteristics. Natural disturbance processes Rock surfaces show a wide variety of textures and shapes related to surface alteration processes, sometimes initiated under burial conditions. Their texture and morphology depend on intrinsic and external factors. Intrinsic factors are: mineralogy, mineral size, the presence of open and closed fissures, dykes and their mineralogy, flow and orientation structures formed during the magma cooling process, laxities parallel to the wall surface, etc. External factors generally relate to the climatic and environmental conditions to which the rocks are exposed. Other factors related to environmental conditions and which also affect the morphology of the outcrops are: the presence of lichens and mosses, and the existence of patinas with calcifications and other chemical precipitates. The primary weathering processes affecting granitic rocks are hydrolysis (which transforms potassium feldspars into kaolinite), oxidation (which significantly impacts biotites), crystallization of salts (which contributes to the separation of mineral grains), and temperature fluctuations. Furthermore, the presence of lichens and mosses plays a role in the processes of alteration and/or stabilization of the rock. The geomorphological features of the walls that influence climbing (Figure 1) vary greatly in shape and size [1,4]. Minor shapes range from a few millimetres to several centimetres. The most common features include micro-roughness, micro-sheets, hardened surfaces, micro-dikes, and xenoliths. Larger forms encompass morphologies typical of granitic modeling, such as tafoni, piles, dykes, fractures, and grooves.