In his opinion, the case before us is classically suitable for the definition of a sinkhole, since the pool was built above an ancient underground cave in chalk soil, whose opening had previously been blocked by filling with clay and stones without engineering control. Continuous and significant water penetration from the pool leak over the course of two years caused the filling material to drift downwards into the cave, until the fill roof lost its stability, collapsed and caused a sudden collapse of the pool floor.
Prof. Friedman clarifies that sinkholes are not unique to the Dead Sea; while in the Dead Sea they are formed by the dissolution of salt layers due to the drop in water level, natural sinkholes are known worldwide in areas of carbonate rock (such as limestone and chalk) due to prolonged water penetration that creates karstic caves. In addition, many sinkholes are formed around the world as a result of human activity over existing caves, and the professional literature documents many cases of sinkholes that developed under leaking swimming pools that accelerated underground erosion.
- The two experts were questioned about their opinions and their opinions were discussed.
First, because the case does not geologically fit the definition of a sinkhole, and geologically it is the mass of limestone or salt, and in the Land of Israel there are sinkholes only in the Dead Sea area (Dr. Yarkoni). The second is that a sinkhole is not only the mass of limestone or salt, but can also be on top of a cavity created by the collapse of the ground surface on top of an existing cave or other cavity (Dr. Friedman).
Dr. Yarkoni clarified that the type of rock in the settlement of Karmei Yosef and the surrounding area is not suitable for the production of sinkholes that are formed over millions of years (even if they can be accelerated by humans, such as in the Dead Sea). Because there is a fundamental difference between piping - which can also be caused by a structural failure of one kind or another, or even due to heavy rain than a sinkhole that is located underground, and melts over a certain period of time (p. 35 of the protocol).