Cliff erosion – mapping, causes and effects in the coastal zone near Cape Kaliakra (northern Bulgarian Black Sea)

The study covers the coastal slope in the Zelenka locality (northern Bulgarian Black Sea coast). This is a beautiful but also dangerous area due to constant sloping and falling of huge blocks of land on the shore. The slope is composed of Miocene sediments: diatomaceous clays (Euxinograd Formation), unconsolidated aragonite sediments with limestone interbeds (Topola Formation), and a steep limestone rock crown (Karvuna Formation). An assessment of the material eroded from the slope, composed of aragonite sediments of the Topola Formation, for the period from October 2018 to March 2019 was made. The quantities of this material were measured and laboratory tests were carried out on the aragonite sediments. The grain size and plasticity (classification characteristics) of the soil were determined. The surface of the slope is waterlogged (or wet), as water flows down the slope of the contact formed between the Topola and Karvuna formations. The geotechnical studies and mapping of the coastal slope revealed that the erosion processes can affect not only the slope stability, but also of the road integrity, and therefore may pose a real geological risk.