Problems of landslide chronology in the Mátra mountains in Hungary

Abstract. A detailed survey and mapping o f the landslide processes and surface forms in the volcanic middle mountains of Hungary formed in the Middle and Late Miocene was carried out in the past decade. As a result of investigations it can be stated that their occurrence is mainly confined to the areas as follows: a) marginal zones of volcanic mountains, b) steep inner slopes of the former calderas of eruption, c) valley slopes cut into stratovolcanic Structures. In their characteristic regions of occurrence landslide forms are important, in some places even determinant components of morphology. The overwhelming majority of the landforms are no more active and can be considered fossilised. Consequently, landslide processes used to play a significant role in forming slope morphology in previous stages o f geomorphic evolution. Research performed heretofore has provided only rather ambiguous answer to the question concerning the time of emergence of landslides on a theoretical basis. Due to the absence of young sediments traditional stratigraphic methods could not yield satisfactory results. The authors therefore attempted to determine the time of the upfilling of lakes or bogs located in undrained depressions clammed by slides and the minimum age of the landslides through the analyses of borehole samples. In the Mátra sediments upfilling of 7 such depressions were carried out. In several cases pollen diagrams were obtained and in two boreholes radiocarbon dating of samples were performed. The paper summarises the results of the borehole analyses and evaluates pollen records supported by C14 dating in detail. Analyses performed using various methods indicate a beginning of the bog formation in the Early Holocene, consequently landslides occurred presumably in the wake of the Preboreal or prior to that in a warm spell following the Late Glacial. Although these results cannot be extrapolated to all the landslides identified in the two mountains (their number is ca. 20) without more ado nevertheless they are orientating.