Geomorphology research in Jeita cave, Lebanon : speleogenesis study for a scientific valorization of a touristic cave

Poster Session, International Congress on scientific research in Show Caves, Karst Research Institute ZRC Sazu, SloveniaJeita grotto is one of the longest cave in the Near-East region with more than 10 000 meters of underground network gallery. Situated 18 km north of Beirut, it holds the record of the longest stalactite in the world with 8.2 meters long. In 2011, Jeita cave was one of the 28st finalists for the selection of the new seven natural wonders of the world competition. It was the only cave site represented in this final list. Adding to these points, the touristic value of this site that makes Jeita cave the first visited site in Lebanon: explored totally by lebanese cavers in 1950's, it was opened to the public in 1958 and later on in 1969, after the discovery of the upper galleries. Jeita cave receives, in average, more than 280 000 visitors per year (Source: les sommets du tourisme, Chamonix, 2009). With all these natural and historical characteristics, most visitors do not know the scientific value of this site. Lack of visual and material information in the touristic path encourage the visitors to ask speleologists about the cave, when they are on site. One of these questions was about the genesis of the grotto: how this big underground canyon of 75 meters deep was formed? These informational requests encourage us to put up new challenges throughout our study on the cave geomorphology and speleogenesis. Therefore, a research project on Lebanon's karst geomorphology was carry out since 2009, by Saint Joseph University of Beirut in collaboration with EDYTEM laboratory UMR 5204-CNRS, France. These studies aims at reconstruct: i) speleogenic evolution of caves based on geomorphologic indicators, ii) karstogenesis reconstitution related with the downcutting of the Mediterranean hydrographic network (Antelias and Kelb river), iii) palaeogeographical reconstitution of these tow valleys. On of these cave was Jeita grotto located on the north side of Kelb river. We wanted to expose these results to the public concerning Jeita site, once the cave history uncovered. Our work consists at reconstituting the downcutting stages of Jeita underground canyon according to the karst base level, which is the kelb river. The methods used to our study were based on: i) completing a high-resolution geomorphology map of the cave combined with detailed cross-sections of the canyon and retrace paleohydrological records from sediments sequence. On one hand, six specific sites were selected in he upper and lower galleries and surveyed. The detailed map led us to complete an inventory of erosion processes (dissolution, fluvial, collapse) that participated in he cave formation. Adding to this method, 26 detailed cross-sections were completed and showed us the cave original morphology assigned to fluvial erosion of the underground river. While geomorphology map helped to understand the spatial distribution of deposits, cross-sections illustrated the erosion processes succession in the canyon and revealed common shapes and aspects on different sites. Combining these tow methods has lead to reconstruct four stages of the Jeita canyon history based on a relative chronology approach. On the other hand, tow in-fillings sequences in both upper and lower galleries were completed. A grain-size analysis has revealed the deposit dynamics and the palaeoflows of the underground river such as velocity variations and flows directions. The paleohydrological records contributed at the comprehension of Jeita Underground River. As these scientific results helped us to uncover the cave history, our suggestion is to respond on tourist's scientific curiosity by implementing educational boards in different locations, outside and inside Jeita cave. These backboards consist on showing specific cross-sections and exposing cave dimensions and its different genesis stages. A general scheme on Jeita canyon downcutting compared to Kelb valley could be added next to one of the cave entrances. Our duty as cavers and karst scientists is, not only to gather data (through photos, maps and description...) on caves and publish them in our bulletins, but also inform and instruct the public on the scientific value of Lebanon's underground natural heritage. Communicating science can be one of the best mean to preserve natural sites, such as Jeita cave