Alluvial fans at Cala Gonone (Sardinia), a fast developing touristic village: origins, hazards and potential risks

Abstract

The study area of Cala Gonone in NE Sardinia (Italy) consists of a wide terraced re-entrance/valley crowned inland by carbonate hills and, near the coast bounded laterally and partly floored by thin basaltic lava lying over carbonate bedrock. In this re-entrance, several inland alluvial fans (500 m length by 700 m wide) have developed, and a local ~ 30 m high, about 10 m wide (thick), 400 m long scarp body-remnant of semi-consolidated alluvial fan deposits is exposed along the coast. The fans experience depositional events mostly developed during the late Pleistocene. They although nowadays dormant may be reactivated by major rainstorms during strong climate changes. In these last few decades, the touristic village of Cala Gonone has been rapidly expanding over the mid to lower parts of two coalescing alluvial fans (Stadium and Gustui) and along the coastal marine scarp edge (Palmasera alluvial fan system). The village thus may become exposed to natural hazards if extreme climatic conditions may re-occur. Moreover, rock falls and the instability of the costal scarp due to wave erosion may add addition hazards for habitations built near the scarp crest and visitors to the frontal replenished beach. As commonly occurring elsewhere since antiquity, the risk perception of such events is low because of the centennial, millennial of longer recurrence. Such perception does not negate the hazards but a long event recurrence may be accepted as a reasonable risk for the human’s activity. Nevertheless, serious consideration should be given to potential problems and plan and build for amelioration and defense. The evidence of what environmentally did and could still happen in the Cala Gonone and similar other area is in part clearly imprinted on the landscape: geology, geomorphology, and relative details in the stratigraphy and sedimentology of the deposits.

Paleoecological reconstruction during the Holocene in the Middle Branch of Bue Marino Cave (Sardinia, Italy)

“…The causes of this change may only be hypothesized through the results of this study and could be attributable to an increase of terrestrial contributions in the cave, possibly due to the climatic instability that followed the optimum climatic (Giraudi et al, 2011) and/or to the geomorphological changes occurred along the coast, with the progradation of alluvial fans (De Falco et al, 2022; Pascucci et al, 2022).…”

“…This karst system is formed by the combination of coastal processes (action of waves on structurally weak areas) combined with the dissolution of carbonates due to the mixing of fresh and salt waters (D’Angeli et al, 2015 and references therein). It developed within the Mesozoic Limestone, which suffered the Quaternary climatic and sea level fluctuation, which determined an intense erosion leading to the development of coastal apron-alluvial fan systems (Pascucci et al, 2022) and the formation of numerous underground cavities (Cabras et al, 2008).…”

“…Among all dating methods, luminescence dates the last exposition to the sunlight of minerals such as quartz and feldspar before burial and, thus, the deposition time (Lian and Roberts, 2006). The method has been successfully applied to Holocene to Middle Pleistocene Sardinian deposits using quartz and potassium-rich feldspar (K-feldspar) minerals (Casini et al, 2020;Cocco et al, 2019;Pascucci et al, 2014Pascucci et al, , 2022Sechi et al, 2013Sechi et al, , 2018aSechi et al, , 2018bSechi et al, , 2020Sechi et al, , 2023Zucca et al, 2014). Recently, Andreucci et al (2017) successfully applied the luminescence method to date wind blow sediment filling the Bue Marino cave, which is part of a vast karst complex of the Gulf of Orosei.…”