Evolution of the Białka valley Pleistocene moraine complex in the High Tatra Mountains

Abstract

Pleistocene moraine complexes with glacial deposits well beyond the last glacial maximum (LGM) limit are rarely formed and preserved in the face of small valley glaciers due to topographic, tectonic, and glacier-size-specific factors. Here, we show the results of detailed mapping of the Pleistocene terminal moraines in the Białka Valley (High Tatra Mountains, Western Carpathians) formed by a 13 km long valley glacier. To portray post-depositional denudation process in the moraines, we mapped the size distribution of moraine boulders and measured their weathering index using the Schmidt Hammer test. In the moraine complex, three morphological units were distinguished from the younger (inner) to the oldest (outermost): Łysa Polana (ŁP), Rusinowa Polana (RP), and Hurkotne (H). The ŁP unit (LGM) features hummocky moraine relief which does not occur on the two older units. In contrast, surface boulders occur on the ŁP and RP units, but they have been cleared from the oldest H unit due to long-lasting erosion. Consequently, the most weathered boulders occurred in the intermediate age RP moraine (~MIS 6). Our results show that in Central Europe, the persistence of surface granite boulders in the landscape cannot be much longer than that of the penultimate glaciation, which highlights the problem of exposure age dating of old moraines in this area. Both pre-LGM glaciations extended ca. 1 km beyond the LGM moraines, but in the case of the H glaciation, this length reduction (7%) was accompanied by a 220 m valley incision at the glacier front. Therefore, the Białka valley glacier was able to achieve a self-limiting effect even in an area of considerable tectonic uplift. We suggest that vigorous, wet-based glacier erosion occurred in areas with high rates of ice accumulation and mass turnover in the windward NW part of the High Tatras exposed to orographic induced precipitation.