Published in enviro.philica.com
Here we investigate in satellite image time series of Google Earth a phenomenon linked to the decreasing level of the Dead Sea, the appearance of sinkholes. Keywords: Satellite Image Time Series, Google Earth
Sinkholes of Dead Sea in Satellite Image Time Series
Amelia Carolina Sparavigna
Department of Applied Science and Technology, Politecnico di Torino, Italy
Abstract: Here we investigate in satellite image time series of Google Earth a phenomenon linked to the decreasing level of the Dead Sea, the appearance of sinkholes.
Keywords: Satellite Image Time Series, Google Earth
The Dead Sea, also called the Salt Sea, is a salt lake between Jordan and Israel, which lies in the Jordan Rift Valley, having as main tributary the Jordan River. It is a hypersaline lake, with 34.2% salinity (in 2011) , being then 9.6 times as salty as the ocean . The name of the lake comes from this salinity which does not allow life to flourish in it.
This Sea had a great importance for the local history and environment: it was a health resort for King Herod the Great, and, in the past, it had been the supplier of products such as asphalt for ancient Egyptian and potash for fertilizers . Today, its salt and minerals are used to create cosmetics.
In 1930, its surface was 1,050 km2 and its level was 390 m below sea level. From this year, the Dead Sea has been monitored continuously . In recent decades, the Sea has been rapidly shrinking because of diversion of incoming water from the Jordan River. The southern end of the Sea is fed by a canal maintained by a company which is converting the sea's raw materials. To preserve the Sea, in December 2013, Israel, Jordan and the Palestinian Authority signed an agreement for laying a water pipeline to link the Red Sea with the Dead Sea . In January 2015 it was reported that the level of water is now dropping by three feet a year .
The Dead Sea level drop is causing the appearance of large sinkholes along the western shore. It is linked to freshwater that dissolves salt layers, creating subsurface cavities that collapse forming the sinkholes . In Ref.6, it was told than in 2006, more than a thousand sinkholes had developed along the western coast of the Sea since the early 1980s, all occurring within a narrow strip less than 1 km wide. The researchers observed that the appearance of sinkholes was a highly dynamic phenomenon that was accelerating in the recent years of their observations. The sinkholes had been produced by the salt dissolution by groundwater, a cause evidenced by direct observations in test boreholes. However, as told in , the entire phenomenon was involving the Sea is a hydrological chain reaction, which "starts by intensive extraction of fresh water upstream of the Dead Sea, continues with the eastward retreat of the lake shoreline, which in turn modifies the groundwater regime, finally triggering the formation of sinkholes".
The sinkholes of the Dead Sea are the subject of several researches, among them [8-13]. In 2015, in , the authors tell that more than 4,000 sinkholes have formed since the 1980s (four times the number given in 2006). Their formation rate accelerated in recent years to > 400 sinkholes per year. Moreover, an association between sinkhole sites and land subsidence is revealed by interferometric synthetic aperture radar (InSAR) measurements .
The highly dynamic phenomenon of sinkhole, such as the drop of the dead Sea level can be easily observed in the satellite images of Google Earth. In fact, this virtual globe is offering for some large areas of the Dead Sea, several images with high resolution, arranged in SITS (a SITS, Satellite Image Time Series, is a set of images taken from the same scene at different times). SITS offers opportunities for understanding how a location is changing, and, in some cases, also predicting the future changes. Therefore, it is a fundamental tool for environmental monitoring and analysis of land-cover dynamics, such as for monitoring the land use by human activities [14-17]. In some previous papers, for instance, we have shown examples of SITS to investigate the motion of sand dunes [18-22].
Let us consider here some sinkholes near Ein Gedi, as given in SITS by Google Earth. Ein Gedi is an oasis, near Masada and the Qumran Caves. The series is given in the Figures 1-4, from May 2002 to July 2010. Note that the edge of the sea moved of about 145 meters in eight years.
We can also use the images of May 2002 and July 2010 for having a composed image for an easy comparison (see Figure 5). The image had been obtained using GIMP, the GNU Image Manipulation Program. In it, it is impressing how the edge of the Sea moved. However, the drop of the Sea is continuing. In the Figure 6, we can see in a HERE map, a more recent image (2014) of the same location.
Fig.5: Using Figs.1 and 4, combined by means of GIMP, the GNU Image Manipulation Program, we can easy see how the edge of the Dead Sea moved in eight years.
Fig.6: A HERE map gives us a more recent image (2014) of the same location of Fig.5.
The satellite images are clearly showing that the Dead Sea is drying up. Of course, it is also evident from them, that the number of sinkholes is rapidly increasing, making the shores of the Sea a more dangerous place today than in the past. If the satellite images had a high enough resolution, a monitoring of sinkholes could be made precisely and directly from local population, through services such as Google Earth. Shores of Dead Sea then are places where a direct monitoring from above of the local environment could help in a safe management of human activities.
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Sparavigna, A. (2016). Sinkholes of Dead Sea in Satellite Image Time Series. PHILICA.COM Article number 575.