Lava Farms were areas worked by the Ta-Matoran in Ta-Wahi and Ta-Metru. When the Matoran lived on Metru Nui, objects could be crafted in Ta-Metru from piped-in molten Protodermis, then easily shipped into other districts for assembly and use. On the island of Mata Nui, things were not so simple owing to the number of Rahi serving Makuta who made the manufacture and transporting more difficult. Ta-Matoran began harvesting lava from the Mangai Volcano and cooling it down, then using tools to shape it into items that might be needed. These would then be shipped via underground tunnels to other villages. The Bohrok's initial attack on Ta-Wahi damaged some lava farms.
All of these on Mata Nui were destroyed by the Bohrok.