Sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as the Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky, an underground stream or river may be visible across its bottom flowing from one side to the other. Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or in other soluble rocks, such as gypsum, that can be dissolved naturally by circulating ground water. Sinkholes also occur in sandstone and quartzite terrains. As the rock dissolves,
Egma Sinkhole Egma Sinkhole EGMA Sinkhole (), a.k.a. Peynirlikönü Sinkhole, is a sinkhole and the deepest cave in Turkey. It is located at Sugözü village of Anamur, Mersin. The sinkhole is deep and long. EGMA stands for Evren Günay - Mehmet Ali Özel Sinkhole. Beginning in 1993, the cave was being explored by BÜMAK (Boğaziçi University Speleological Society). A flash flood caused Mehmet Ali Özel to lose his life inside the cave in 2001. In 2004, with the help of members of the Bulgarian Speleological Federation, the BÜMAK team recovered Mehmet Ali's body and also reached the deepest point of the cave.