Morphotectonic control on drainage network evolution in the Perachora Peninsula, Greece

In tectonically active areas drainage systems are often influenced by the type, geometry, and recent activity of regional and local faults. In the Perachora peninsula, eastern Gulf of Corinth (Greece), most drainage networks are influenced by neotectonic processes and eustasy. Two major east–west trending fluvial systems (Perachora and Pissia) in the southwestern part of the peninsula are affected by faults of similar orientation. Detailed geomorphological mapping was performed focusing on knickpoints, gorges, planation and depositional surfaces, alluvial fans and talus cones. Longitudinal river profiles and hypsometric curves of their basins were constructed utilizing GIS technology. The two drainage systems exhibit opposite network asymmetries. The Pissia network is well developed south of the main channel while the Perachora extends to the north. The analysis of the longitudinal profiles of the main stream channels denotes that they exhibit different evolutionary trends. The Pissia stream has a “transverse” drainage crossing the active Loutraki fault, while the Perachora stream has a “parallel” evolution as it has the same orientation as the Loutraki fault. The drainage system of Pissia is much older than the Perachora as a large part of the latter was underwater in Late Pleistocene times. The combination of eustacy and vertical tectonic movements has led to the development of four marine terraces corresponding to previous high sea-level stands during Oxygen Isotope Stages (OIS) 5e, 7e, 9c and 11c. Following the analysis of the longitudinal profiles and the hypsometric curves two depositional surfaces were verified at Perachora village. The first surface at 280–360 m and the second one between 120 and 160 m are probably related to marine terraces 11c and 7e respectively. The development of the present drainage systems of Perachora and Pissia in the Late Quaternary depends mostly on the fault tectonism of the two main offshore fault systems of Xylokastro and Loutraki resulting in the uplift of marine terraces to heights of more than 300 m, but also due to the inland faults (Pissia and Alepochori) which created depositional surfaces and knickpoints. Sea-level changes have played a secondary role in the development of the drainage systems.