Situated in Italy by the seaside, it's hard to comprehend that our beach activities, whether laying a towel on the sand or playing a game of beach racquet, are taking place over the geological history of Italy. Beneath our soles and sun umbrellas could lie rocks that once formed the towering Alps, remnants from ancient volcanic eruptions, or golden stones washed down from the Apennines. This is because the beaches of Italy stem from its mountains.
These beaches are produced from the material eroded within river watersheds and transported downstream, with every part of Italy contributing, from the Alps to the Apennines. Just as the geology of Italy and its mountains is intricate, so is the composition of its beaches.
Embarking on a tour of Italy's beaches isn't just a scenic experience but a geological exploration. To identify the origins of these beaches, it's essential to trace the rivers. As Massimo Moretti, a professor of Sedimentology at the University of Bari, explains, rivers transport material from the rocks in their catchment areas, which are broken down by erosion.
In the marine environment, another transportation method comes into play: currents. Generated by waves, these currents transport sands towards and away from the shore and even along the coastline. This process, known as littoral drift, follows the prevailing winds and enables the sands to travel considerable distances along the coast.
Our journey starts with the Po and the northern Adriatic region. The Po carries materials from the Alps and the northern Apennines, leading to a diverse range of sediments that shape the nearby beaches. The grey sands of the Po, comprising materials from the Alpine mountains, are prominent along the northern coast of Emilia-Romagna. However, every river contributes, creating a mix of sand flows. In Rimini and the Romagna Riviera, sediments from the Apennines are driven north by wave-induced currents.
The rivers in the northern Adriatic, such as the Brenta and Piave, transport sediments from the Eastern Alps, originating from the light limestones of the Dolomites. The Tagliamento, for instance, flows into the beach of Lignano Sabbiadoro, a reservoir of golden sand. The light sands of the Marche and Abruzzo regions are sourced from the erosion of the Apennines, where limestone is prevalent. Hence, the beach is a fusion of rocks, explaining the variations in color between different sand grains.
Moving between Liguria and Tuscany, from the mouth of the Magra to Livorno, the Magra, originating from the Tuscan-Emilian Apennines, also brings sediments from the Vara to the sea. The Vara, rich in dark materials with greenish hues, originates from the Ligurian Apennines. These sands are swept southwards, reaching Marina di Pietrasanta, where they converge with the lighter sediments of the Arno, which are carried north and south to Livorno. As the sands shift, the coarser grains are left behind, resulting in the Marina di Pietrasanta convergence zone containing the finest sand from Bocca di Magra to Livorno.
We talked about transport via rivers and sea. Before continuing the tour, let's explain what happens upon arrival, where the sand settles forming the beach. Which is far more than the strip we frequent on vacation: the emerged part is only a fraction of that underwater. Waves and storm surges move sand, transporting it toward the coast or out to sea. There is more than just sand, then. There are gravel beaches, which often form near river deltas.
There are vast karst areas where much of the precipitation is swallowed into the deep water table without flowing to the surface. In the Ionian part of Salento, however, bioclastic beaches are created: these are those formed by fragments of shells and other marine organisms, broken by wave action. They consist almost entirely of calcium carbonate, the inorganic component of shells and other animal remains.
Calcium carbonate is white and gives the sands a snow-white color. These beaches actually depend on a plant: posidonia, which forms underwater meadows. "These shell organisms live in the posidonia and when they die their remains end up on the beach with those of the posidonia. This decomposes, the shell fragments remain. So posidonia is crucial in providing material for these particular beaches, as well as a natural barrier that limits coastal erosion: its remains should not be removed from beaches," Moretti concludes. And yet in general in beaches an organic component is always there.
Similar is the mechanism that created an extraordinary formation: the Pink Beach on the island of Budelli (SS), Sardinia. It is composed of shell fragments of Miniacina miniacea: it is a foraminifera, a protozoan that builds a pink-colored calcareous shell. It lives on posidonia and when it dies it arrives on the coast with the remains of the plant. Sands of biological origin can also be found in pocket beaches, the "pocket beaches." "These are those limited by two headlands, on which the waves, as they break, lose energy causing all the shells of organisms to be deposited in the bay between them," Moretti explains. "Normally, unless they are home to a river, pocket beaches have little terrigenous sediment (from erosion of older rocks, ed.). A very small part comes from erosion of the rocks of the headlands themselves. The rest, as in the pocket beaches of Puglia, comes from the shells of the many organisms that inhabit the seabed."
Some widespread minerals also create clear beaches. "One of these is quartz, which is transparent and is well present in our beaches because it is very abundant in the rocks. The same goes for other clear minerals such as feldspars. And clear can also be sediments that come from limestones," Moretti summarizes.
Let's delve into the mesmerizing world of mixed beach materials. The exquisite Is Arutas beach in Oristano, Sardinia is a natural spectacle crafted from quartz. Erosion has shaped the quartz granules into white and pinkish grains, sprinkled with hues of green. Similarly, the Cala Violina beach in Scarlino, Tuscany, is another quartz marvel. However, its uniqueness lies not in its color but in its musicality – it croons like a violin when walked upon. The resilience of quartz allows it to withstand erosion, unlike other materials, giving it its distinct sonic effect.
Switching from light to dark, let's explore the origins of darker beaches. Many owe their existence to volcanic materials, such as basalt. The Aeolian Islands' black beaches, including Sabbie Nere at Vulcano and Ficogrande at Stromboli, are products of active volcanoes. However, some dark sands are remnants of extinct volcanoes, such as the minerals from Mount Vulture in Basilicata that reach the Adriatic. These minerals, denser than quartz, are transported selectively, creating unique beachscapes between Margherita di Savoia and Otranto.
Common in magmatic rocks, minerals like amphiboles, pyroxenes, and magnetite are often found in these dark sands. Magnetite, an iron mineral found in basaltic rocks, boasts a high density and strong magnetic properties, making it easily attracted by a magnet.
The color palette of Italian sands doesn't stop at black. The Terranera beach on Elba Island, rich in iron ore, is a sight to behold. This dark, shimmering beach is studded with fragments of magnetite, hematite, pyrite, and iron ores, remnants of the island's mining activities. Meanwhile, the black beach of Cala Jannita in Maratea, Basilicata, owes its color to blackish limestones and dolomites that feed it, proving that not all limestones are clear.
Completing the spectrum are the red and orange sands of Italy. The beach at Porto Ferro in Sardinia showcases a vibrant orange hue, thanks to the iron oxides present in its sandstones. Indeed, the place where we lay our towels for a day at the beach deserves more than just a cursory glance.
Post a Comment