Coastal types of graben: the Gulf of Gokova, Mugla-SW Turkey

Abstract

Grabens are formed under the influence of extensional forces in a normal fault system. The Gulf of Gokova is an active graben located in SW Turkey. Active grabens such as the Gokova enclose highly faulted rocky coasts. Despite the existence of these rocky coasts, examination of google earth images, field studies, DEM analysis and previous studies in the Gulf of Gokova graben revealed that there could be different types of coasts in the region. In this study the factors causing the occurrence and potential environmental effects of the diverse coast types are evaluated. By using the Fairbridge (2004) coastal classification system, the coast types identified in the Gulf of Gokova graben can be classified as; A. Soft-less consolidated-erodible; A1: relatively Insoluble: detrital and loose beach, A2: soluble: beachrock and eolinite B. hard-cliffed-rocky, B1: longevity of hard-rock coast and B2: fault controlled cliffs. The percentages of these classes generally decreased from B1 (79%), A1 (12.4%), B2 (8.3%) and A2 (0.3%) in the study area. As a result of longshore currents, A1-type coasts usually develop as large plain adjacent streams and also in pocket beaches as narrow-long strips near rocky coasts. A2 type is observed in one location within the Gokova region, possibly due to local environmental conditions. However, B1 type developed in peridotites, cherty limestone and cliffs probably because of the active fault system and where the fault plane cut the coast, B2 type occurred. Possible threats to the Gokova region can be attributed to sea level rise owing to tectonism and global warming. It is anticipated that inundation, coastal erosion and salt water intrusion may also affect it.