Geomorphological Survey: July 9-18, 2008

While the geologists map the territory geologically and identify potential raw materials that could play a role in local craft production, the geomorphologists try to identify the formation and changes in the physical landscape over the last ten millennia (the Holocene). Their goal is to understand natural (climatic change, catastrophic events, landslides, earthquakes) and hu-man (man caused erosion, land use, deforestation, etc.) roles in all these events. From the very beginning of our research in 1990, this research has been directed by Etienne Paulissen (K.U. Leuven), working in close collaboration with palynologists Marleen Vermoere and David Kaniewski (CAS). In view of his approaching retirement in a couple of years, Paulissen has gradually ceded his role to Gert Verstraeten. During the first two weeks of the 2008 cam-paign, Gert, together with Bert Dusar, Jozefien Hermy, Martijn Claes, and Koen Vereycken, (all K.U. Leuven), continued working in the alluvial plain of the Büğdüz Çayı. It is one of the largest river catchments in the territory of Sagalassos and provides the shortest link between the site and the fertile plains around Lake Burdur. Since 2006, we have studied the sediments within this river catchment in order to reconstruct the river morphology in antiquity; quantify the total amount of sediment storage within this valley system for different time periods; and determine the sources of the sediment. In a later stage, spatial variability in sedimentation rates within the Büğdüz Çayı will be coupled with information on settlements patterns through time.

So far, we have performed 36 detailed sediment cores in the alluvial plain. This complements data from 75 sediment cores collected during the 2006 and 2007 field campaigns. For the middle part of the valley, several cores confirm the findings from last year: a braided river system characterised by coarse gravel deposits is covered here by 2-3 meters of fine sediment. Radiocarbon dating on charcoal fragments indicates that the braided river was active until at least 800 B.C., i.e. the Early Iron Age. The majority of the fine sediments, however, postdate A.D. 1000. Deforestation and intensive land use from the Hellenistic period onward seem to have initiated intense soil erosion on the hill slopes, resulting in major alluviation (up to 1.5 mm/year) so intense that the valley bottom got clogged with fine earth material creating the current landscape. These results are in contrast with findings obtained during previous years by Paulissen's geomorphology team in smaller catchments like Bereket and Gravgaz. In those catchments, high sedimentation rates during the prosperous Roman Imperial period declined sharply afterward, while in the Büğdüz River system they remained rather stable, illustrating the greater buffering capacity of larger fluvial systems in response to important human-induced land use changes since classical times. Nevertheless, these land use changes have brought about changes in the main sediment texture deposited (i.e. transition from gravels to silt) and river morphology (transition from a braided to a single-thread channel). In the lower parts of the catchment, however, sediment deposition is less important. This is because of the steeper river gradient (as a result of active tectonic movements) which prevents sediments to be deposited.