Tatvan lies on the southern shore of Lake Van, the largest lake in Turkey and the largest soda lake in the world. Because the lake lies 1648 meters above sea level, it is one of the largest mountain lakes in the world and with its depth of 451 meters also one of the deepest.

Its only outlet towards the Euphrates was blocked by the Nemrut volcano about a million years ago.

The volcano Nemrut Dağı (not to be confused with the famous mountain of the same name further northwest with the sanctuary of King Antiochos on its top) is 3050 meters high and erupted for the last time in 1881. 

The peak was completely blown away by a gigantic explosion during an eruption. The result was a huge crater basin with a diameter of almost 7 km. In the western half, one of the largest crater lakes on earth was formed.