Phases of alluvial fan development in a loess area, Lublin Upland, E Poland

Holocene alluvial fans are a record of the evolution of the environment and human impact over the last 10 000 years. The study presents the structure of fans at the mouth of gullies as well as their development in the loess areas of the Lublin Upland. Sediment-soil sequences of seven alluvial fans and the adjoining flood sediments and dry valley bottom sediments were studied in detail. The development of fans occurred in three phases: i) the Eneolithic; ii) the middle and late Bronze Age and the Hallstatt period and iii) the Middle Ages and the modern times. The middle phase consists of two sub-phases while last phase consists of three sub-phases: the early Middle Ages; the Little Ice Age; the 19th and first half of the 20th century. These phases were interspersed with longer or shorter periods of stabilization of the alluvial fan surface. The different course of land use changes in the catchments was the reason for this metachronous development of the alluvial fans. Our studies indicate that heavy and catastrophic rainfall and rapid thaw had a considerable role in the development of the alluvial fans. The establishment of roads along the axes of valleys and across the slopes had a key impact on alluvial fan development. The deforestation of the catchment was not an essential condition for the formation of gullies and alluvial fans.