Sea of Liquid Sand
The Sea of Liquid Sand was a large area of quicksand located southwest of Vulcanus. Any creature foolish enough to wander into the region quickly found itself sinking into the mire, never to be seen again.
The Sea of Liquid Sand was a massive area stretching along the southwestern edge of the Bara Magna desert, occupying the area south of the Dunes of Treason. The dusty Skrall River and the Vulcanus Lava Flow emptied into this region. The villages of Tajun and Vulcanus were located along its edge.[2, 3]
The Sea of Liquid Sand was a dreaded mire of quicksand and was located to the south of Vulcanus. While there were safe paths through the sea, they were few in number and difficult to spot. Virtually anyone or anything that entered the region never emerged again.
If one went too far south of Vulcanus, one ended up in the Sea of Liquid Sand, a massive bed of quicksand few ever escaped.
Mata Nui's actions to restore Spherus Magna presumably stopped the Sea of Liquid Sand from encroaching on Bara Magna.