Holocene flooding and river development in a Mediterranean steepland catchment: The Anapodaris Gorge, south central Crete, Greece

Abstract

Many Mediterranean steepland rivers are flanked by extensive alluvial and colluvial deposits, but Late Quaternary histories of channel and hillslope behaviour remain poorly constrained, primarily because of the limited availability of material suitable for dating. Study of a 4.8 km long reach of the Anapodaris Gorge, located in the lower part of an ∼ 500 km 2 catchment in south central Crete, reveals a succession of well preserved, coarse-grained (predominantly cobble to boulder) and fine-grained (predominantly silt to sand) alluvial deposits that locally interfinger with, or are overlain by, coarse colluvial and tributary stream deposits. Detailed ground surveys, geomorphological mapping, sedimentological investigations, and geochronology (optically stimulated luminescence, radiocarbon, and lichenometry) have allowed detailed reconstruction of the timing and pattern of sedimentation and erosion over the mid to late Holocene. Widespread, coarse-grained aggradational episodes at c. 4.86–4.20 and c. 3.40–3.00 ka have been punctuated by incisional episodes and coarse sediment export, resulting in a suite of alluvial terraces. Comparison with other proxy Mediterranean environmental change records, particularly high-resolution marine and lake records, suggests that these aggradational/incisional episodes were primarily climatically driven, reflecting changes in the balance between hillslope/tributary sediment supply and high-energy flood events. By contrast, phases of widespread fine-grained aggradation at c. 1.90 ka, 1.13 to 1.10 ka, 0.85 to 0.70 ka and 0.21 ka provide evidence for decreases in flood competence, possibly coupled with up-catchment historical land use changes. Since the middle of the nineteenth century, several large floods have formed localised boulder berms and splays and have contributed to stripping of the fine-grained deposits from many parts of the gorge. The findings from the Anapodaris Gorge demonstrate the sensitivity of Mediterranean steepland catchments to rapid and/or short-lived Holocene climate change but also highlight the need for higher resolution data on historical and prehistoric land use changes.