Djerdap Gorge (Iron Gates)
The geomorphological axis of the whole Djerdap area is the Djerdap gorge, formed along the Danube through the Southern Carpathians, between the Pannonian plain on the west and the Dacian plain on the east. With a length of over 100 km, this is the longest through gorge in Europe. The southern side belongs to Serbia, and the northern side to Romania. The gorge stretches from the rock Babakai, which protrudes from the Danube opposite to the Golubac medieval fortress, to the village Gura Văii in Romania. It actually consists of four gorge sectors and three basin-like wider parts, in this order: Gornja Klisura (Upper Gorge, Golubac Gorge), Ljupkovska Kotlina (Liubcova basin), Gospodjin Vir Gorge, Donjomilanovačka Kotlina (Donji Milanovac basin), Kazan Gorge, Oršavska Kotlina (Orşova basin), and Sipska Klisura (Sip Gorge). The name Djerdap was formerly related only to Sipska Klisura, but later on started to be used for the whole gorge. In the diverse geological composition, the rocks that dominate are schists, limestones and sandstones.
Erosional forms dominate in the fluvial relief, – river valleys (with river terraces or without them), while aggradational (accumulation) forms are present in a lesser extent – in the drainage areas of the direct tributaries of the Danube, due to slowing of water after the construction of the artificial lake. Geographer Jovan Cvijić detected a series of river terraces in the relief of Djerdap, which witness the phases of the Danube incision. Most of the terraces are visible only in segments, but in a systematic overview, their hypsometric positions show the sequence of incision. The highest terrace (at 430 m a.s.l, or 370 m above the original Danube level) is called the Kalfa terrace. The next one, at 260 m above the Danube, is the Kazan terrace. According to Cvijić, these two terraces are of Pontian age (Lower Pliocene). Further incision formed the terraces at 210 m, 150-160 m, and 90-115 m above the Danube level, which are related to the Upper Pliocene. Quaternary age is attributed to three lowest terraces, at relative heights 60-63 m, 27-30 m, and 10 m (Cvijić, 1921).