Geomorphosite Characterization Method for the Purpose of an Aspiring Geopark Application Dossier on the Example of Maritsa Cirque Complex in Geopark Rila, Rila Mountain, SW Bulgaria

Abstract

Rila Mountain in Southwest Bulgaria is the highest mountain on the Balkan Peninsula. During the Pleistocene ice ages, large ice shields covered higher parts of the mountain forming cirques and through glacier valleys. Maritsa Cirque Complex is the through head of one of the most powerful glaciers, carved out in the mountain. Since it was nominated for a geosite of esthetic and scientific value within Geopark Rila, in order to improve, precise, and unify the method of characterization and presentation of geomorphosites in alpine environment, it was chosen as an example description to serve as a model for characterization of the other geomorphosites in the geopark. Maritsa Cirque Complex is well outlined in its natural boundaries on an area of 5.29 km² including five composite cirques: Maritsa, Trionite, Preslap, Malak Bliznak, and Mancho. The cirque complex is incised in the Eocene granite of the Musala Body of the largest batholith on the Balkans – the Rila-West Rhodopes Batholith. The Maritsa Cirque is the deepest Rila’s cirque with a diameter of 1500 m and displacement of 572 m between its bottom and the highest peak Musala (2925 m). In the middle of it, a younger cirque is incised with a diameter of 700 m, in which two tarns (Maritsa Lakes) are formed. The other cirques are smaller and higher, hanging over the main valley. The glacial and post-glacial deposits are represented by bottom moraines and supraglacial scree slopes, representing clusters of angular granite blocks and boulders on the slopes of the cirques and glacier valley. There are large scree cones at the base of the avalanche furrows on the cirques walls which are the product of frost weathering in the active periglacial alpine belt of Rila. The cirque complex is deeply incised into the Early Miocene Kapatnik denudation surface, the highest Rila’s peneplain elevated at 2400 m above sea level, which shaped the rounded Rila’s ridge before the Ice Ages. The present slope of this surface in Zavrachitsa area shows that the highest peak of Rila during the Pleistocene was just above the Maritsa Cirque and the surrounding peaks – Musala, Maritsa Chal, Mancho, and Twin Peaks – were situated on its slopes. The reconstruction of the Pleistocene paleorelief based on a simple GIS analysis of the modern relief shows that the height of the dome-shaped Rila’s top peak Paleo Musala before the Pleistocene glaciations was more than 3000 m. Easily accessible and well-preserved glacial and post-glacial landscapes provide an excellent opportunity for demonstrating the geological processes and destructive glacial activity that shaped the highest mountain on the Balkans. The continental significance of this geomorphosite is complemented by the remarkable petrographic diversity of the granitoids of the Rila-West Rhodopes Batholith and metamorphic rocks contained therein, intersected by numerous pegmatite, aplite and quartz veins, vein-like granite bodies, diorite, and granite porphyry veins, suitable for illustrating crystallization process, magmatic/metamorphic structures, and textures and demonstrating the principle of the crosscutting relationships in geology. Standard geosite’s characterization in the form of scientific dossiers, including the most important information about the genesis and geoconservation features, will provide a reliable basis for estimation and comparison of their individual merits necessary for inclusion in the geosites inventory of Geopark Rila. It will contribute to the assessment and promotion of the geosites through development of itineraries linking geosites in alpine environment with appealing information panels containing well-interpreted scientific information directed to the general public.