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Archives of Nethys

Pathfinder RPG (2nd Edition) Pathfinder RPG (1st Edition) Starfinder RPG

Rules Index | GM Screen
Mastering the Wild / Hazards and Disasters

Volcano (CR Varies)

Source Ultimate Wilderness pg. 150
Magma churns beneath the earth’s surface throughout the world, and in places where there are weaknesses in the crust, it can erupt outward in violent conflagrations. Volcanic dangers such as lava, lava bombs, poisonous gas, and pyroclastic flows are covered in the GameMastery Guide, but there are additional dangers that a volcano can present.

Earthquake: The force with which volcanoes erupt can shake the earth, so earthquakes are common during volcanic eruptions. Depending on the nature of the terrain, these disastrous events can cause any of the effects listed in the Earthquake section: they can hinder movement, cause buildings to collapse, open fissures in the ground, and topple structures both large and small. They can also trigger tsunamis.

Lahar: A lahar is a churning slurry of mud and debris created when intense heat melts the glaciers or snow atop a volcano. A lahar can travel hundreds of miles beyond the volcano, devastating everything in its path. Motion alone keeps a lahar in liquid form. When a lahar strikes a creature, it deals the damage listed in Table 4–8: Types of Lahars below (Reflex half, at the listed DC). For creatures caught in a flowing lahar, use the rules for being swept away in flowing water with a DC 25 Swim check. Anyone trapped under a lahar cannot breathe and must attempt Constitution checks to avoid suffocation. Lahars can be hot or cool depending on the events that cause them. A hot lahar deals 2d6 points of fire damage per round to those trapped by it. As a lahar slows, it settles to the consistency of packed earth, entombing those trapped within or beneath. See the Cave-Ins and Collapses section for rules on digging out a buried creature.

Table 4-8: Types of Lahars

TypeCRDepthWidthSpeedDamageReflex Save DC
Minor910 feet100 feet100 feet/round8d615
Typical1025 feet500 feet250 feet/round8d620
Massive1250+ feet2,500+ feet500 feet/round16d625


Steam Vent: Major eruptions of steam or boiling water often precede an eruption and deal between 4d6 and 15d6 points of fire damage (Reflex half, DC = 10 + number of damage dice). The radius of such bursts is typically equal to 5 feet per damage die. Mild steam vents are as hot as saunas and have a sulfurous odor.

Volcanic Ash: Erupting volcanoes spew ash, which can obscure vision and cause creatures to choke as if it were heavy smoke. Prolonged contact with hot ash deals 1d6 points of fire damage per minute. Clouds of ash can linger in the atmosphere, darkening the sky for weeks or even months and leading to colder temperatures and prolonged winters. This combination of cold and lack of sunlight hurts crops, and it can cripple food supplies and lead to famines. On the ground, ash buildup creates difficult terrain—not only is it slippery, but it might conceal other hazards. In heavy eruptions, a blanket of ash several feet thick can eventually blanket the region downwind of the volcano. Over the long term, however, this volcanic ash becomes fertile soil.

Volcanic Lightning: Ash clouds can generate powerful lightning strikes. These strikes typically deal between 4d8 and 10d8 points of electricity damage and are unusually difficult to dodge (Reflex half, DC = 15 + number of damage dice).