Fire geysers are holes protruding from the floor, pointing up, that occasionally spit out columns of fire. Unlike regular geysers, fire geysers are harmful to the leaders and Pikmin that are not Red Pikmin or Bulbmin. Leaders can become invulnerable to these after the Scorch Guard is salvaged, however.
In Pikmin, these geysers are in static locations, spit fire at regular intervals, and cannot be destroyed (although they can be punched by Captain Olimar, even if it is pointless). In Pikmin 2, they are actually damageable, and if destroyed, they will stop ejecting fire, making them harmless. Although any Pikmin type can damage a fire geyser, Pikmin that are vulnerable to fire are likely to get burned if the geyser shoots out a column of fire during the attack. In Pikmin 3, fire geysers act like the ones in Pikmin, except they are not visible. The only way to tell a fire geyser is somewhere is when a pillar of fire emerges from the ground. This can catch unwary players by surprise. It should be noted that leaders in Pikmin 3 can punch fire geysers, but the latter won't take any damage.
Their main purpose is to block pathways, encouraging the player to use Red Pikmin to transverse the area, as other Pikmin types may catch on fire. In Pikmin, fire geysers cause a considerable amount of damage to Captain Olimar, and may hit him multiple times during the same discharge.