March 21, 2012
New Research Shows Venice Is Now Slipping And Sinking
Once thought to have stabilized, new measurements reveal that Venice continues to sink slowly.
For a while, global rising sea levels were thought to be the cause for the growing waters in the famous canals.
Yehuda Bock, a geodesist with Scripps Institution of Oceanography at the University of California, San Diego, in La Jolla, California, said about the rising: “Venice appears to be continuing to subside, at a rate of about 2 millimeters a year.”
“It´s a small effect, but it´s important.”
Bock also noted that sea levels are not only rising in the canals, but also in the Venetian lagoon at the same rate. Given that the city is built on and around this water, the level at which it rises against the buildings will double relative to the elevation of the city. If Venice and its surroundings continued to fall at this rate, Bock predicts the city could be 3 inches lower in 20 years than it is today.
Working with colleagues from the University of Miami in Florida and Italy´s Tele-Rilevamento Europa, a company that measures ground deformation, Bock analyzed a combination of GPS and space-borne radar data (InSAR) to measure the levels of Venice and its lagoon. By comparing this data from a similar set of data taken a decade earlier, Bock and his team concluded that Venice was sinking at a rate of 2mm a year.
The team´s findings will be published on March 28th in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union.
“Our combined GPS and InSAR analysis clearly captured the movements over the last decade that neither GPS nor InSAR could sense alone” said Shimon Wdowinski, associate research professor of Marine Geology and Geophysics at the University of Miami.
The GPS and InSAR data revealed more than a 2mm subsidence per year. Bock and his team also discovered that Venice appears to be tilting as well, at the rate of about 1mm eastward per year. Because of this, the western sections of the city now sit higher than the eastern sections. Bock says the GPS data was beneficial in this part of the study, as InSAR only provides data about elevation relative to other sites.
More than a decade ago, the question of “Is Venice sinking?” became a major issue. It had been thought that groundwater pumping from beneath the city and hundreds of years of compacted ground were causing the city to sink. Scientists later said the city was only settling. This news didn´t stop city officials from ceasing all groundwater pumping, and in 2000, it had been thought that the city had stopped sinking.
“It´s possible that it was stable in that decade, and started subsiding since then, but this is unlikely,” Bock said.
This current slipping and sinking are likely due to natural causes, such as tectonic slipping.
As Venice nears a multi-billion-dollar effort to install flood-protection walls that can be raised to block against incoming tides, the frequency of floods in the city is growing. Bock´s research is important, if not controversial to the city, especially in regards to the construction of these walls.