The phenomenon of land subsidence in Venice: a story of fragile equilibrium
- Claude Gauthier
- Dec 30, 2024
- 2 min read
The gradual subsidence of the Venetian soil, known as subsidence, is a complex process resulting from several natural and human factors that intertwine to slowly but inexorably alter the level of the city in relation to the sea.
For 150 years, the region has been sinking at a rate of 2.6 mm per year.
Venice is getting bogged down
The ground is subsiding, due to the movement of tectonic plates, the weight of the buildings that are supported by wooden stakes and the construction of channels and structures in clay soil. The city is subject to the influence of strong winds coming from the Sahara and blowing towards the north, increasing the amplitude of the tides. The general sea level is rising, a consequence of the accelerated melting of glaciers.
Historical tide level measurement
Measurements of tidal level variations began in 1871 on a scientific basis.
To better understand the extent of the flooding in Venice, tidal measurements taken before 1871 would be needed. Scientist Dario Camuffo (1941 - ), an expert in atmospheric physics, has been studying the magnitude of tides since 1969. To obtain ancient data, he studies 17th century paintings to assess the height of the tides.
He compares the water level that appears on the canvases, in relation to the current levels.
He used the paintings of Antonio Canaletto (1697 – 1768) and his student Bernardo Bellotto (1721 – 1780).
The particularity of these two landscape painters is that they used the camera obscura to reproduce the scene and trace with great precision the detail of the buildings. Dario Camuffo, author of the research of the sea levels of Venice
Their precision was such that they reproduced in paint every stone of the buildings and every detail of the structures.
When you look at the paintings, you can't tell if it was a high or low tide scene. You have to find a marker that is independent of sea level and that appears on the paintings. In fact, you find a biological indicator, which is the algae that appear on the buildings at a level where they are flooded daily by the sea.
By calculating the height of the green ring over the years, Camufo calculated an increase in the level
apparent sea level of 61 cm between 1750 and today, with an uncertainty level of 11 cm (digging of canals, appearance of motor boats, etc.).
The study confirms an exponential growth of the sinking rate of Venice.
Details, painting by Caneletto
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