Hydrothermal(Volcanic) Vents

In 2013 James Cameron also stated that the style would be influenced by the master navigator culture of the small pacific civilizations of Micronesia. He was exposed to these cultures during his time on these islands during preparation for his dive in the Marianas Trench.[13] 
Not long after KRZ had been in Development at Lightstorm, Cameron went to the Marianas Islands and a deep sea dive to the Marianas Trench where he was captivated by the Hydrothermal Vents there. He gave a TED talk on his experience in 2010.
https://james-camerons-avatar.fandom.com/wiki/Avatar_2