The southern regions of the Matoran universe were largely unexplored by the Matoran, and the farthest south anyone had ever been was the volcanic island of Artidax. Whatever lay beyond it was a mystery. Artidax was the third in a long chain of twelve islands that ran from north to south down the western leg of the Matoran universe.
[Artidax] was a volcanic island far south of anything on any chart.
Artidax loomed out of the mist and was an island of black sand and jagged rock, volcanic peaks and strange Rahi arcing and wheeling through the sky. Despite the bright light that played off the waters around it, the island seemed to be in perpetual shadow. Its shore consisted of black sand. Krika rigged the sands to react to the presence of a Makuta by dragging him down into the ground. This was to keep Miserix from escaping or another Makuta from finding him and finishing him off.
The whole island was volcanic. It had minor eruptions over the years, but nothing major. Tahu and Kopaka quelled these eruptions.
Artidax had multiple volcanoes.
The Great Beings' scroll instructed the Toa Nuva to quell the volcanoes on Artidax because the Great Beings knew that they would potentially be active if Mata Nui fell asleep.