The Inactive Lava Zone is characterized by large, arching structures and walls of hardened lava with occasional steaming lava falls. It is composed of two distinct areas and can be found at 900 to 1300 meters down, well below the limit of a Seamoth (even when equipped with a Seamoth Depth Module MK3) - making an upgraded Cyclops and Prawn Suit the only vehicles to be able to navigate through it. The player must be extremely careful when navigating this biome, as touching the lava on the floor of the Inactive Lava Zone can completely deplete the player's health in seconds and the temperature applies constant damage unless the player has a Reinforced Dive Suit. It also contains the rare resource Kyanite, which is used in crafting some Prawn Suit and Cyclops modules.
The Inactive Lava Zone can be accessed through two entry points located in the western and eastern wings of the Lost River, being the Mountains Corridor and the Tree Cove, respectively.
There is an unidentified area below the Inactive Lava Zone accessed by a small hole/drop off. It extends from about 1300-1600 meters in depth, and small holes and drop offs extending down to about 1700 meters. It looks like a completely barren version of the safe shallows with no flora or fauna.
At the center of the Inactive Lava Zone is a large chamber, with occasional veins of lava and spires of hardened rock. Titanium, Copper Ore and Ruby can be found on these spires occasionally. Lava rivers can be found in narrow corridors around the area with Silver Ore, Crystalline Sulfur and Diamond found scattered around them. A large structure called the Lava Castle can be found in the middle of the chamber, with small, partially-collapsed volcanic domes scattered all over the floor of the chamber itself. These can have some Ruby, Magnetite, and Gold on them. Many skeletal remains of Reaper Leviathans can be found here due to the Sea Dragon Leviathans infrequently coming to the surface to hunt them and bring them to the central chamber to feast.
Near the Lava Castle, there are multiple lava falls, leading directly into the Lava Lakes. They can be found easily by following the streams of molten lava on the floor of the Chamber.
The Inactive Lava Zone Corridor is a small section of the region which links the Lost River and Inactive Lava Zone together. There is only one in the game, it is accessed via the Tree Cove. The other entrance is located in the Mountains Corridor which leads directly to the Inactive Lava Zone and then to the Lava Castle.
The Inactive Lava Zone Corridors are characterized by large cavernous corridors of hardened lava. Veins of active lava can be found regularly, sometimes ejecting molten boulders. The Corridors continue well below all other biomes and converge into a central chamber. Resources such as Nickel Ore and Crystalline Sulfur are frequent in this biome which comes in useful in the fabrication of certain vehicle upgrades.
The Lava Castle is a special area within the Inactive Lava Zone. The entrance located in the Lost River Mountains Corridor that connects to the Inactive Lava Zone can lead you here.
The Lava Castle is a huge structure of volcanic rock possessing a rather large interior cavern, obsidian pillars, and thermal vents. Various cave systems lead to the center of the castle, which is a large chamber featuring a lava pool with tall spires of rock around its edges. The structure seems to be the breeding grounds of Lava Lizards as it is the only place their eggs can be found.
The Alien Thermal Plant is found inside the Lava Castle.
The Lava Pit is a large pit found on the outskirts of the main chamber. The walls of the pit are covered in large grooves, at the northern edge of the pit one of the grooves acts as an entrance to the Lava Lakes The lighting in this area is much brighter than the surrounding areas of the Inactive Lava Zone. It resembles a volcanic dome and most of the resources contained within are Diamond, Gold, Lithium, Titanium, Quartz, Lead, Magnetite and Large Uraninite Deposits.
Raw Materials normally found in Harvesting Nodes in the area can be found naturally on the seabed of the region, this being the only circumstance for resources such as Titanium or Gold to be found in this state.
- There were once multiple corridors leading to the Inactive Lava Zone that were found in the Crash Zone, Deep Grand Reef, and the Dunes.
- The Inactive Lava Zone is the hottest and deepest biome to naturally support Flora.
- Some of the resources in this biome that are commonly found inside harvesting nodes (such as Titanium, Copper Ore, Gold, Silver Ore and Lead in the Lava Pit) can be found without being inside an outcrop.