Continental ridge
A mountain ridge that separates river systems is called a watershed or a drainage divide. This geographic feature determines the direction in which water flows, dividing the flow of water into different river basins.
Its the Danube river and Danube plain separates Romania and Bulgaria. There are no mountaneous border between the mentioned two countries. And Carpathian mountain range of Romnia or Balkan mountain range (most northern mountains of Bulgaria: none of them serves as border.
A mountain range that separates river systems traveling in opposite directions is called a "continental divide." This geographical feature delineates the watershed areas, where water on one side flows toward one ocean or sea, while water on the other side flows toward another. The most well-known example in North America is the Continental Divide of the Americas.
A deposit that forms where a river leaves a mountain range is called an alluvial fan. This fan-shaped deposit is created as the river slows down and deposits sediment and debris that it has carried from the mountains.
Alluvial fan.
The Continental Divide of the Americas is an example of a mountain ridge that separates river systems. Further examples include Northern Divide or Laurentian Divide.
It begins in the Caucasus Mountain Range
The Indus River begins in the Himalayas mountain range in Tibet.
Aral Mountains.......divide Europe and Russia
continmental dividecontinental divide
The Ural Mountains and the Caucasus Mountains both form separating mountain ranges between Europe and Asia.
Appalachian, the oldest mountain range in the US