Rocky coast geomorphology and erosional processes: a case study along the Murgia coastline south of Bari, Apulia – SE Italy

Many sites along the Apulian coast (SE Italy) are composed of weathered and fractured carbonate rocks affected by intense erosion and the development of slope instabilities. Here, coastal morphology was mostly produced by Quaternary tectonics, the severe and selective action of modern erosion by sea waves, and locally, was strongly conditioned by human influences. In addition, due to the carbonate nature of rock masses, the role exerted by karst processes has to be considered. This paper provides a critical review of the common eroding processes and factors affecting coastal morphology in a typical Mediterranean coastal carbonate environment. A stretch of the Murgia coastline south of Bari (between San Vito and Polignano a Mare) made up of cliffs and shore platforms interrupted by small pocket beaches was considered. For qualitative and quantitative assessment of shoreline recession, the coastal stretch was monitored by means of field surveys between 1997 and 2003. Furthermore, a comparison of vertical aerial photographs covering the period 1966–1997 (scales 1:33,000, 1:10,000 and 1:5000), topographic maps (scales 1:5000, year 1987, 1:2000, year 1982), and archival terrestrial photographs taken since the 1930s was also employed. In some zones, characterised by a gently sloping shore platform, a significant shoreline retreat was calculated at about 20 m in the last 100 years (0.2 myr− 1), which was caused, above all, by human activity. Here, in fact, the presence of small ancient coastal quarries and artificial salinas is widespread; they are located where soft and porous calcarenites crop out. The cliffs are characterized by different types of landslides, with various complex mechanisms of rock slope failure. Cliff recession is episodic and discontinuous in time and space, and occurs in response to single large sea storms, such as that which occurred in January 1999. Between 1997 and 2003, the cliff retreat rates vary within a range of 0.01–0.1 myr− 1 and, in general, decrease where the coast is composed of fine-grained limestones and increase where medium-grained biocalcarenites crop out. Examples of erosion hazard indicators and mass movement typologies are illustrated.