Conditions and morphogenetic role of the 2018 and 2021 debris flows in Starorobociański Cirque, Western Tatra Mts.

Abstract

In this study we used geomorphologic mapping, precipitation analysis and archival photomaps to study debris flows in the Starorobociański Cirque, which were renewed in 2018 and 2021. Debris flow in 2021 was most likely the largest single flow recorded in the Polish Western Tatras in the twenty first century. It reached a length of about 870 m and it covered an area of ​​0.62 to 0.65 ha. We set July 14, 2021, as the date of debris flow initiation and 52.1 mm·d−1 as its threshold value. This is one of the lowest values provided in the literature for such flows in the Western Tatra Mts. On the contrary, debris flow which occurred July 18, 2018 was linked to threshold value of 150.5 mm·d−1. On the basis of former debris flow occurrence as well as precipitation analysis we interpret the appearance of debris flow in 2021 as an effect of short and intense rainfall.