The morphology of the land of sinkholes - a complete Mitzpe coast area

המורפולוגיה של ארץ הבולענים – אזור חוף מצפה שלם
The site is located on the shore of the Dead Sea on a soft plain of clay deposits that were exposed when the lake receded to the east. From this vantage point you can see high alluvial fans made of sand, pebbles and conglomerate next to the clay plains. The alluvium arrives and is stratified in the coastal area by the flood waters of the streams (steps, Hevar beds, etc.), while the clay that builds the clay plains sank directly from the lake water. The clay existed as a suspension in the lake water and sank from the water only in areas of still water and without agitation. Types of sinkholes The sinkholes that form in the clay plains are wide, open and usually flooded with groundwater. The sinkholes formed in the alluvial fans are usually dry and remain closed with a thin roof until the dramatic moment of collapse. After the collapse, they remain with steep sides, unlike the clay sinkholes whose sides are graded and moderate. Because of this, the fan sinkholes are much more dangerous than those in the clay plains. How were the sinkholes formed? On the bottom of the Dead Sea are constantly layers of sediments. Mostly it is clay, sometimes it is thin layers of limestone crystals and sometimes when the sea is very salty layers of salt sink. Drilling and simulations of seismic waves have shown that along the shores of the Dead Sea there exists within the clay layers at a depth of about 30 m a layer of salt about 7-10 m thick. A remnant of a short period when the lake was extremely salty. As long as the lake water level was high, this layer of salt was embedded in the salty groundwater and did not melt. As the lake level dropped, the saline groundwater level also dropped. They migrated following the lake to the east and their place was taken by fresh ground water that originates from the springs of the Coppice Cliff to the west. This fresh water flowed through long cracks that cracked the sequence of clays and salt. The water dissolved the layer of salt along the cracks creating a line of mass cavities. The spaces created along the cracks grew larger over time, the salt dissolved and flowed with the water while the ceiling of the space began to collapse inward until a thin ceiling remained that could collapse with weight loading. In the sinkholes of the clayey area, there is usually no ceiling left and the collapse is gradual.