Acting as a divide between Sicily and Calabria, the Strait of Messina is a maritime pathway that connects the Tyrrhenian Sea to the Ionian Sea. There's a potential for the strait to be bridged in the near future, with work planned to commence in 2024. The strait, not a channel, owes its name to the distinct chemical and physical compositions of the two bodies of water it connects. The strait is shaped somewhat like a funnel, measures approximately 33 kilometers in length, and varies in width from just over 3.1 kilometers to a maximum of 16 kilometers. The ferry ride across the strait, between Rada San Francesco (Messina) and Villa San Giovanni (Reggio Calabria), can take 20 to 45 minutes depending on the route.
The Strait of Messina is marked by strong currents and high-speed winds, coupled with depths varying from 60 to 100 meters, and significant seismic activity. These elements contribute to the complex engineering challenges involved in constructing the proposed "Strait Bridge." The bridge, once completed, will be a 3.3-kilometer long, single-span, cable-stayed suspension bridge, with an additional 300 meters of land sections, making it the largest of its kind. One anticipated construction hurdle involves setting the enormous foundations to support the bridge's piers.
Understanding the Formation of the Strait of Messina
Calabria and Sicily were once a single landmass, but intense tectonic activity involving three converging plates in the Mediterranean led to their separation over 125,000 years. This geological process created a vast underwater canyon. The National Research Center (NRC) refers to the Strait of Messina as a hub of active faults, making it "one of the most seismically active zones in the entire Mediterranean region."
This seismic activity, including the devastating 7.1 magnitude earthquake of December 28, 1908, has driven the separation of the two southern Italian regions. This earthquake, tied to the Messina-Taormina fault and followed by a tsunami, resulted in over 60,000 deaths and major destruction in Messina and Reggio Calabria. Despite the seismic challenges, the construction of a single-span bridge is a feasible yet significant challenge, as several bridges have survived earthquakes of magnitude 7.0 and above.
Exploring Beneath the Strait of Messina: Morphological and Geological Aspects
Nestled beneath the Strait of Messina is a colossal tectonic depression, within which lies a unique underwater mountain that peaks at the strait's shallowest point, the "saddle." Two slopes extend from this peak, one toward the Tyrrhenian Sea and the other toward the Ionian Sea. The Tyrrhenian slope has a gentler morphology, gradually deepening to 2,000 meters near the island of Stromboli, while the Ionian slope forms a steep decline, sinking hundreds of meters just a few kilometers from Gazirri and Punta Pezzo, the two settlements closest to the saddle.
The bathymetry is also quite variable in the central portion, where areas that reach even more than 1,200 meters deep alternate with the presence of striking submarine valleys characterized by steep slopes such as that of Scilla. The bottom of the depression is also covered with immense sand deposits, which accumulate due to cross currents from the two joined basins. Such a seabed, with a not inconsiderable depth even close to the saddle, can pose a significant problem because of the need to build exceptionally large foundations. The impact to the underwater environment and the ecological balances of the Strait's rich ecosystem would also be devastating. The interplay of currents fuels the phenomenon of "upwelling," which promotes a thriving biodiversity by transporting nutrients and plankton from the bottom to the top.
A dangerous stretch of sea due to currents
The currents in the Strait of Messina are considered particularly treacherous because of their ability to generate large eddies with a speed of more than 9 kilometers per hour, as explained by Professor Vittorio Villasmunta. In ancient times, these strong tidal currents-especially the Charybdis current-sucked boats, killing the crews. Mythology's giant sea monsters Scylla and Charybdis are said to have been inspired by this devious feature of the sea arm. The currents of the Strait of Messina are quite peculiar, and among the first to study them in depth was a team of scientists from the Institute of Geophysics in Trieste, who conducted analyses aboard a military ship in the early 1920s.
The most significant aspect lies in the fact that between the Tyrrhenian Sea and the Ionian Sea there is a difference in height (up to thirty centimeters) due to the discrepancy between the high and low tide phases. This causes water from one to flow into the other and vice versa. The waters of the Tyrrhenian Sea are less dense and lighter, while those of the Ionian Sea are heavier. Their interaction gives rise to various vertical and horizontal phenomena such as the aforementioned eddies, eddies and real waves, processes that can bring deep-sea creatures to the surface. The construction of an immense engineering project such as the Messina Bridge is likely to get in the way of these phenomena and create significant ecological imbalances.
The very strong winds that often blow across the Strait should also not be underestimated, so much so that the fluctuations that would result for such a bridge could lead to its temporary closure on very windy days. Engineers will have to strike a perfect balance between torsional rigidity and deformability of the structure without breaking legal limits (made even more stringent by the fact that high-speed trains would also have to pass over the bridge).
A risky crossroads of active faults
Beneath the Strait of Messina lies a large depression, the "Messina Valley," a veritable canyon technically known by the name of Graben. It is a strip of the earth's crust that is "open" due to the geological processes in place, related to the faults that converge here and have contributed to the separation of Sicily and Calabria for tens of thousands of years. That the two Italian regions were once united is also shown by the characteristics of the Aspromonte and Peloritani Mountains in northeastern Sicily, which are similar both lithologically and geologically. In practice, they were part of the same chain, but were separated by the aforementioned earthquakes.
A recent CNR study published in Scientific Reports showed that the Strait area is affected by "a complex fault system where different tectonic regimes coexist over short distances: extensional, transcurrent and compressional." This detail underlies the extremely violent earthquakes that have been released here in historical times. In addition to the catastrophic one of 1908, there is also the seismic sequence between February 5 and March 28, 1783 (which caused more than 30,000 deaths) and the earthquake of November 16, 1894. Basically, a huge catastrophe every 100 years.
High seismicity is a not insignificant problem for the construction of a gigantic infrastructure like the Messina Bridge, but bridges like the one in the 2011 project (very long and single span) have inherent earthquake-proof properties precisely because of their remarkable flexibility. Large earthquakes that have struck suspension bridges, such as the Akashi Kaikyo in Japan and the Golden State in the United States, for example, did not suffer significant damage precisely because of the oscillatory capabilities.
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