Geothermal springs form where magma heats underground water to extreme temperatures. This hot water periodically erupts at the surface, collecting into pools of heated water of varying temperatures. In some cases, the resulting hot springs are relatively harmless, and communities often pop up nearby, as the therapeutic nature of the spring attracts visitors. But in some cases, geothermal springs are heated to the boiling point or hotter, or they might pose other dangers to the unwary.
GMs should feel free to modify the damage amounts and saving throws of a geothermal spring to take into account the spring’s size and water temperature.
Fumarole (CR 1): Fumaroles occur when the groundwater is boiled away before reaching the surface, so when it erupts from vents in the ground, it does so as steam, often carrying toxic gases along with it. The type of gas released by a fumarole depends on the composition of the surrounding ground. Some fumaroles, referred to as solfataras, emit dangerous levels of sulfuric gas. The eruption rates of fumaroles vary from every few minutes to every few hours.
A creature within 5 feet of an erupting fumarole must succeed at a DC 15 Reflex save to avoid the eruption. On a failed save, the creature takes 2d6 points of fire damage from the scalding steam. If the fumarole emits sulfurous gases, each creature within 30 feet of the erupting fumarole must succeed at a DC 20 Fortitude save or take 1 point of Constitution damage and become nauseated for 1d4 rounds. On a successful save, the creature negates the Constitution damage and is sickened for 1d4 minutes instead of nauseated. This additional effect is a poison effect.
Geyser (CR 3): Geysers form when surface water seeps down into the earth and meets rocks heated by the proximity of magma. The pressure created by the boiling water causes the water to erupt on the surface. The rate, frequency, and length of eruption vary from geyser to geyser. Some issue a single, sustained geyser at a regular interval. Others go through a series of short eruptions, lasting only a few seconds each for hours at a time, and then go dormant for several hours or even days. The jets of water from erupting geysers also vary in height, with some erupting upward of 100 feet in the air.
A creature within 5 feet of an erupting geyser must succeed at a DC 15 Reflex save to avoid the eruption. On a failed save, the creature is knocked prone and takes 2d6 points of fire damage. Creatures immersed in the geyser’s jet each take 5d6 points of fire damage and must succeed at a DC 15 Reflex save or be forced out of the geyser’s jet and knocked prone. Creatures within 10 feet of a geyser (but beyond 5 feet) each take 1d6 points of fire damage from the boiling hot spray falling on them.
Hot Spring (CR 2): Common hot springs contain pools of warm water, but in some, the water is heated to nearly boiling. Exposure to this water deals 1d6 points of fire damage per round. Total immersion deals 5d6 points of fire damage per round; damage continues for 1 round after total immersion, but this additional damage is 1d6 points of fire damage.
Mud Pot (CR 1): Mud pots are springs that mostly contain hot bubbling mud instead of water. The mud’s color depends on the amount and type of minerals in the mud. Mud pots range widely in size and depth, with many found in clusters. Gases from within the earth can cause mud pots to boil over or shoot mud a short distance into the air. Exposure to a mud pot deals 1d3 points of acid damage and 1d3 points of fire damage per round of exposure. Total immersion in a mud pot deals 1d6 points of acid damage and 1d6 points of fire damage per round; damage continues for 1 round after total immersion, but this additional damage is only 1d3 points of acid damage and 1d3 points of fire damage. Moving through a mud pot is like moving through a bog.
Pathfinder Roleplaying Game: Ultimate Wilderness © 2017, Paizo Inc.; Authors: Alexander Augunas, John Bennett, Robert Brookes, John Compton, Dan Dillon, Steven T. Helt, Thurston Hillman, Eric Hindley, Mikko Kallio, Jason Keeley, Isabelle Lee, Jason Nelson, Stephen Radney-MacFarland, Alex Riggs, David N. Ross, David Schwartz, Mark Seifter, Jeffery Swank, and Linda Zayas-Palmer.