The Mountains of Dhoom are a chain of peaks created during the Breaking of the World. During the Breaking, the volcano of Shayol Ghul, then an island, became the epicenter for the destruction wreaked by the Hundred Companions after the Dark One tainted saidin. New landmasses arose, and the Mountains of Dhoom formed during this time. The Mountains of Dhoom appear to encircle the northern polar regions of the world, and stretch right across the Westlands, the Aiel Waste, Shara and Seanchan. It is believed they even continue underneath the waves.
The mountains appear to be black, jagged and lifeless, likely a result of the Blight that surrounds and corrupts them. They tumble into the sea in a confused morass of islands and cliffs. The waters north of the mountains in the Aryth Ocean are called the Dead Sea and are not hospitable. It is unknown if the same is true off the coasts of Shara and Seanchan.
In the Westlands there are numerous narrow passes through the Mountains of Dhoom, used by Shadowspawn to menace the Borderlands throughout much of history. With the expansion of the Blight, few of these passes are directly guarded. The largest and most significant such pass is Tarwin's Gap, north of the fortress of Fal Dara in Shienar. Given that the Trolloc Wars also ravaged the Aiel Waste and Shara, it can be assumed there are passes through the mountains there as well.
The Mountains of Dhoom in Seanchan were named by soldiers and sailors in Luthair Paendrag Mondwin's invasion force, who noted their identical appearance at the same latitude to the mountains in their homeland. It is assumed that the Seanchan patrol and guard any passes through the Mountains of Dhoom into their territory. However, the extent of such precautions given the extinction of Trollocs and Myrddraal in Seanchan is unknown.
The worldwide extent of the Mountains of Dhoom is made clear on the world and continent maps in The World of Robert Jordan's The Wheel of Time.