Sonar map reveals secret life of seabed
Haaretz May31th 2007
By Zafrir Rinat
Israeli scientists have been studying the seabed along Israel's coast for many years. But they've been groping in the dark, not entirely understanding its precise structure. Now, however, thanks to sonar technology, that is changing. High-quality sonar scanning is being used to produce maps more detailed than ever before. Practical applications include planning of ports and artificial islands, as well as monitoring greenhouse gasses and delineating marine nature reserves.
The new mapping project has been moved ahead in recent years by researchers from Tel Aviv University, the Israel Oceanographic and Limnological Research Institute (IOLR), and the Survey of Israel. The project focuses on the continental shelf - the area of the seabed up to a few hundred meters from the shoreline. One of its main results is detailed imaging of the northern seabed, from Haifa to Rosh Hanikra.
Arik Golan of the IOLR explains that the sonar system on the institute's research vessel was brought to Israel from the U.S. by Israeli geologist John Hall, and had been developed originally for the U.S. Navy. The mapping, which was led by Roni Sadeh of Tel Aviv University, was implemented by measuring 850 million reverberations from the seabed at depths ranging from eight to 900 meters, during voyages totaling 4,218 kilometers.
Surveys of the Tel Aviv beach area were also conducted, some of which examined the feasibility of building artificial islands, and some for Golan's research into the effect of the seabed's emission of methane, a gas that contributes to global warming.
Underwater wineries
Imaging of the Haifa Bay revealed the country's geological past. For the first time, the underwater calcareous sandstone (kurkar) ridges can be seen. Sitting parallel to the beach, these ridges show the location of coastlines dating back 10,000 years, when the level of the sea was lower. Calcareous sandstone hills are now to be found up to a depth of 40 meters below sea level. These ridges bear the remains of fishing villages from eras before the Neolithic period.
"Cisterns have been found at a depth of six to seven meters. They may have been wine vats," Golan says, adding that he has also found underwater water cisterns off the Tel Aviv coast using the same methods.
Near Haifa, the continuation of the Carmel range can be seen on the sea floor. A huge canyon was found off of Rosh Hanikra, created from past flows into the sea of the Kziv Stream. Sediment floating northward from the Nile Delta over thousands of years covered part of the seabed, but did not manage to cover the canyon. Between Haifa and Acre, the primordial stream beds of the Kishon and the Na'aman can also be seen.
Geological rifts were also found in a few places. Golan says there is a debate among scholars about the exact location to which the Carmel extended into the sea, and how active some of the documented rifts are.
"Without the information we are collecting now, projects like artificial islands could not be planned, nor could the environmental impact be understood of port construction, such as the blockage of sand flow and the future impact of changes in the level of the sea because of global warming," Golan says.
The imaging project will also allow biological data to be gathered, especially on the underwater ridges, where a varied population of marine animal and plant life thrives. According to the director of the Science Division of the Israel Nature and National Parks Protection Authority, Dr. Yehoshua Shkedi, the project is like topographical mapping on land, allowing us to understand habitats and decide where marine nature reserves should be established. |
