This guide will let you know where to find Lava Geysers in Subnautica, and it will provide you with the best Thermal Power farm locations.
Starting from the coral tube sticking up out of the water, you will need to make your way north or one bump to the left or right of the north until you reach the underwater islands.
You will need to have a sea moth with at least an Mk2 depth module for both locations. It is highly recommended to have a perimeter defense, and hull reinforcement since creatures at both locations will attack you.
The main threat you will encounter in the underwater islands is the bone shark which will try to attack you whenever you get near it. So you have to avoid them, but if they start to get close, you can use perimeter defense to get them to go away for a short time. They also do decent damage to your vehicle; that’s why you need to have hull reinforcement and a repair tool.
Once you reach the underwater islands, you will need to head straight down until you reach the bottom of the underwater island. Then continue straight, and you will eventually come across an area with some holes that are lava geysers in the biome and a few bone sharks that linger around the geysers.
Another good place to make a thermal plant farm is in the inactive or active lava zone/lava lakes.
Again starting from the coral tube that sticks up out of the water, you have to head about 2-3 bumps to the right of southeast until you reach a hole in the ground that leads to the jellyshroom caves.
The main threat you’ll encounter in the caves is the crab snake, which will attack you if you get near them, so you have to avoid them as best as you can. But if they get near, then you can use perimeter defense against them to get them to back off.
Once you are in the jellyshroom caves, you will need to look northwest and head about 1-2 bumps to the left of the northwest. You have to keep moving until you reach a mini entrance that leads to another large opening.
Once you’ve gone through the mini entrance and reached the opening, you have to head west or 1-2 bumps to the right of the west until you eventually come across lava geysers.