Italy experiences a complex environmental phenomenon often described as “sinking,” where its land surface lowers relative to sea level. This occurs due to natural geological processes, the effects of a changing global climate, and localized human activities. Understanding these influences is central to comprehending the challenges facing Italy’s coastal and low-lying regions.
Plate Tectonics and Natural Land Movement
Italy’s geological setting plays a role in its land movement, as the country is situated on the active collision zone between the African and Eurasian tectonic plates. The Adriatic microplate subducts beneath the Apennine Mountains, a process that causes both uplift and subsidence across the peninsula. This ongoing geological interaction results in a naturally dynamic landscape.
The Apennine mountain range, which forms the spine of Italy, is a direct result of these compressional forces. As the Adriatic plate dips beneath the Italian landmass, areas on the overriding plate can experience a gradual lowering. This natural subsidence, driven by large-scale tectonic movements, contributes a few millimeters of sinking per year in various regions.
Beyond large-scale tectonic forces, natural compaction of sediments also contributes to subsidence, particularly in low-lying coastal plains and river deltas. Over long geological timescales, the weight of overlying sediments naturally compresses the underlying layers of sand, silt, and clay, causing the ground surface to settle. This process is especially pronounced in areas like the Po River Delta, where thick accumulations of recently deposited material are present.
Rising Global Sea Levels
Global sea level rise is a distinct factor that exacerbates the perception of Italy “sinking,” especially along its extensive coastline. The primary drivers are the thermal expansion of warming ocean waters and the melting of glaciers and ice sheets worldwide. As Earth’s temperature increases, seawater expands, and meltwater adds to the ocean’s total mass.
Italy, with its roughly 7,600 kilometers of coastline, is particularly susceptible to rising sea levels. The rate of sea level rise for Italy has been estimated at approximately 1.64 millimeters per year since 1903. Projections suggest that by 2050, sea levels along the Italian coast could rise an additional 0.18 to 0.23 meters, depending on future emissions scenarios.
While global sea level rise does not cause the land itself to subside, it leads to a relative increase in sea level. This means that even if the land remains stable, higher water levels result in increased coastal inundation, more frequent flooding, and enhanced erosion, creating the appearance and impact of land sinking. The melting of glaciers, such as the Marmolada in the Dolomites, further contributes to this global trend.
Localized Human-Induced Subsidence
Human activities contribute to localized land subsidence in various Italian regions, often accelerating natural processes. A prominent cause is the excessive extraction of groundwater for agricultural, industrial, and urban uses. When large volumes of water are pumped from underground aquifers, the pore spaces within the soil and sediment layers can collapse, leading to the compaction of these layers and a lowering of the ground surface.
Historical practices, such as the extraction of natural gas or oil, have also been identified as causes of significant subsidence in specific areas. The removal of these subsurface fluids can reduce pressure within geological formations, prompting the overlying land to settle. While some of these practices have been curtailed, their legacy continues to affect land stability.
Heavy urban development and the construction of extensive infrastructure also contribute to subsidence. The weight of buildings and concrete structures can place additional pressure on underlying compressible sediments, leading to further compaction. Cities like Bologna, for instance, experienced substantial subsidence rates, reaching up to 55 millimeters per year before 2000, largely due to intensive groundwater withdrawals.
Vulnerable Coastal Regions
The combined impact of natural geological movements, rising global sea levels, and human-induced subsidence creates particular vulnerability in certain coastal regions of Italy. Venice stands as a widely recognized example, where multiple factors converge to make it exceptionally susceptible to inundation. The city is built on soft, compressible sediments within a shallow lagoon, which naturally subsides at a rate of about 1 to 2 millimeters per year.
Historically, Venice’s vulnerability was greatly exacerbated by extensive groundwater extraction in the mid-20th century, which caused significant additional sinking. Although groundwater pumping was largely halted by the late 1960s, the cumulative effects of natural geological subsidence, past human activities, and global sea level rise have resulted in a total relative lowering of about 23 centimeters over the last century. This ongoing process leads to more frequent and severe “acqua alta” (high water) events.
The Po River Delta, along Italy’s northeastern coast, is a highly vulnerable area. This region experiences both natural subsidence due to sediment compaction and anthropogenic subsidence, historically linked to gas and groundwater extraction. Subsidence rates in parts of the Po Delta have been observed to be as high as 10-15 millimeters per year, with some localized areas reaching up to 30 millimeters per year. Other Italian coastal areas, such as the plains of Sele and Volturno, also face subsidence challenges primarily from groundwater overexploitation for agriculture.