Fall of Mount Gundabad
This article describes a concept which is mentioned in J.R.R. Tolkien's works, but was never given a definite name.
The Fall of Mount Gundabad, took place shortly after Eregion was destroyed.
After the doors of Khazad-Dûm were shut, Orcs, reinforced and commanded by the servants of Sauron, invaded Mount Gundabad and drove the Longbeard Dwarves from their holy site and dwelling. As a result, the Grey Mountains were infested and communication between Khazad-Dûm and the Iron Hills was cut off.