
Archives of Nethys

Archives of Nethys

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

Rules Index | GM Screen | Player's Guide
GM Core / Chapter 2: Building Games

Environment

Source GM Core pg. 90 2.0
Primarily used during exploration, environment rules bring the locales your party travels through to life. You'll often be able to use common sense to adjudicate how environments work, but you'll need special rules for environments that really stand out.

Each of the environments presented in this section uses the terrain rules (Player Core 423) in different ways, so be sure to familiarize yourself with those rules before reading this section. Some environments refer to the rules for climate (page 95) and natural disasters (beginning on page 96). Many places have the traits of multiple environments; a snow-covered mountain might use both the arctic and mountain environments, for example. For environmental features with effects based on how tall or deep they are, those effects vary further based on a creature's size. For instance, a shallow bog for a Medium creature might be a deep bog for smaller creatures, and a deep bog for a Medium creature could be only a shallow bog for a larger creature (and so insignificant for a truly massive creature that it isn't even difficult terrain).

The Environmental Features table (below) lists the features of various environments alphabetically for quick reference. The Proficiency DC Band entry indicates a range of appropriate simple DCs for that environmental feature, while also providing a rough estimate of the danger or complexity of the feature.

Environmental Damage

Source GM Core pg. 90 2.0
Some environmental features or natural disasters deal damage. Because the amount of damage can vary based on the specific circumstances, the rules for specific environments and natural disasters use damage categories to describe the damage, rather than exact numbers. Use the Environmental Damage table to determine damage from an environment or natural disaster. When deciding the exact damage amount, use your best judgment based on how extreme you deem the danger to be.

Table 10-11: Environmental Damage

CategoryDamage
Minor1d6-2d6
Moderate4d6-6d6
Major8d6-12d6
Massive16d6-24d6

Table 10-12: Environmental Features

FeatureProficiency DC Band
AvalancheExpert–legendary
Blizzard—
BogUntrained-trained
CanopyTrained-master
Chasm—
CliffTrained-master
Collapse—
CrowdTrained-master
CurrentTrained-master
DoorSee entry
EarthquakeTrained-legendary
FloodExpert-legendary
FloorUntrained-expert
Fog—
Gate—
Guard—
HedgeUntrained-trained
IceTrained-master
LavaExpert-legendary
LedgeUntrained-master
PortcullisSee entry
Precipitation—
RooftopTrained-master
RubbleUntrained-expert
SandUntrained-expert
SandstormTrained-master
Sewer—
SlopeUntrained-trained
SnowUntrained-expert
StairsUntrained-trained
StalagmiteTrained-expert
StreetUntrained-trained
Temperature—
TornadoMaster-legendary
TreeUntrained-master
TsunamiMaster-legendary
UndergrowthUntrained-expert
Underwater Visibility—
Volcanic EruptionTrained-legendary
WallSee entry
WildfireExpert-legendary
WindUntrained-legendary

Aquatic

Source GM Core pg. 90 2.0
Aquatic environments are among the most challenging for PCs short of other worlds and unusual planes. PCs in an aquatic environment need a way to breathe (typically a water breathing spell) and must usually Swim to move, though a PC who sinks to the bottom can walk awkwardly, using the rules for greater difficult terrain. Characters in aquatic environments make frequent use of the rules for aquatic combat (page 30, Player Core 437) and the drowning and suffocation rules (Player Core 437).

Currents and Flowing Water

Source GM Core pg. 91 2.0
Ocean currents, flowing rivers, and similar moving water are difficult terrain or greater difficult terrain (depending on the speed of the water) for a creature Swimming against the current. At the end of a creature’s turn, it moves a certain distance depending on the current’s speed. For instance, a 10-foot current moves a creature 10 feet in the current’s direction at the end of that creature’s turn.

Underwater Visibility

Source GM Core pg. 91 2.0
It’s much harder to see things at a distance underwater than it is on land, and it’s particularly difficult if the water is murky or full of particles. In pure water, the maximum visual range is roughly 240 feet to see a small object, and in murky water, visibility can be reduced to only 10 feet or even less.

Arctic

Source GM Core pg. 91 2.0
The main challenge in an arctic environment is the extreme low temperature, but arctic environments also contain ice and snow. The disasters that most often strike in arctic environments are avalanches, blizzards, and floods.

Ice

Source GM Core pg. 91 2.0
Icy ground is both uneven ground and difficult terrain, as characters slip and slide due to poor traction.

Snow

Source GM Core pg. 91 2.0
Depending on the depth of snow and its composition, most snowy ground is either difficult terrain or greater difficult terrain. In denser snow, characters can attempt to walk along the surface without breaking through, but some patches might be loose or soft enough that they’re uneven ground.

Desert

Source GM Core pg. 91 2.0
Desert encompasses sandy and rocky deserts as well as badlands. Though tundra is technically a desert, it’s classified as arctic, as the climate is the primary challenge in such areas. Sandy deserts often have quicksand hazards (page 107) and sandstorms.

Rubble

Source GM Core pg. 91 2.0
Rocky deserts are strewn with rubble, which is difficult terrain. Rubble dense enough to be walked over rather than navigated through is uneven ground.

Sand

Source GM Core pg. 91 2.0
Packed sand doesn’t usually significantly impede a character’s movement, but loose sand is either difficult terrain (if it’s shallow) or uneven ground (if it’s deep). The wind in a desert often shifts sand into dunes, hills of loose sand with uneven ground facing the wind and steeper inclines away from the wind.

Forest

Source GM Core pg. 91 2.0
These diverse environments include jungles and other wooded areas. They are sometimes struck by wildfires.

Canopies

Source GM Core pg. 91 2.0
Particularly dense forests, such as rain forests, have a canopy level above the ground. A creature trying to reach the canopy or travel along it must Climb. Swinging on vines and branches usually requires an Acrobatics or Athletics check. A canopy provides cover, and a thicker one can prevent creatures in the canopy from seeing those on the ground, and vice versa.

Trees

Source GM Core pg. 91 2.0
While trees are omnipresent in a forest, they typically don’t provide cover unless a character uses the Take Cover action. Only larger trees that take up an entire 5-foot square on the map (or more) are big enough to provide cover automatically.

Undergrowth

Source GM Core pg. 91 2.0
Light undergrowth is difficult terrain that allows a character to Take Cover. Heavy undergrowth is greater difficult terrain that automatically provides cover. Some sorts of undergrowth, such as thorns, might also be hazardous terrain, and areas with plenty of twisting roots might be uneven ground.

Mountain

Source GM Core pg. 91 2.0
Mountain environments also include hills, which share many aspects of mountains, though not their more extreme features. The most common disasters here are avalanches.

Chasms

Source GM Core pg. 91 2.0
Chasms are natural pits, typically at least 20 feet long and clearly visible (barring mundane or magical efforts to conceal them). The main danger posed by a chasm is that characters must Long Jump to get across. Alternatively, characters can take the safer but slower route of Climbing down the near side of the chasm and then ascending the far side to get across.

Cliffs

Source GM Core pg. 91 2.0
Cliffs and rock walls require creatures to Climb to ascend or descend. Without extensive safety precautions, a critical failure on Climb checks can result in significant falling damage.

Rubble

Source GM Core pg. 91 2.0
Mountains often have extremely rocky areas or shifting, gravelly scree that makes for difficult terrain. Especially deep or pervasive rubble is uneven ground.

Slopes

Source GM Core pg. 91 2.0
Slopes vary from the gentle rises of normal terrain to difficult terrain and inclines, depending on the angle of elevation. Moving down a slope is typically normal terrain, but characters might need to Climb up particularly steep slopes.

Terrain Rules

Environments make frequent use of the rules for difficult terrain, greater difficult terrain, and hazardous terrain, so those rules are summarized here.

Difficult terrain is any terrain that impedes movement, ranging from particularly rough or unstable surfaces to thick ground cover and countless other impediments. Moving into a square of difficult terrain (or moving 5 feet into or within an area of difficult terrain, if you're not using a grid) costs an extra 5 feet of movement. Moving into a square of greater difficult terrain instead costs 10 additional feet of movement. This additional cost is not increased when moving diagonally. Creatures can't normally Step into difficult terrain.

Any movement creatures make while jumping ignores terrain that the creature is jumping over. Some abilities (such as flight or being incorporeal) allow creatures to avoid the movement reduction from some types of difficult terrain. Certain other abilities let creatures ignore difficult terrain while traveling on foot; such an ability also allows a creature to move through greater difficult terrain using the movement cost for difficult terrain, but unless the ability specifies otherwise, these abilities don't let creatures ignore greater difficult terrain.

Hazardous terrain damages creatures whenever they move through it. For instance, an acid pool, a pit of burning embers, and a spike-filled passageway all constitute hazardous terrain. The amount and type of damage depend on the specific hazardous terrain.

Undergrowth

Source GM Core pg. 92 2.0
Light undergrowth is common in mountains. It is difficult terrain and allows a character to Take Cover.

Plains

Source GM Core pg. 92 2.0
The plains environment encompasses grasslands such as savannas and farmland. The most common disasters in plains are tornadoes and wildfires.

Hedges

Source GM Core pg. 92 2.0
Hedges are planted rows of bushes, shrubs, and trees. Their iconic appearance in adventures consists of tall hedges grown into mazes. A typical hedge is 2 to 5 feet tall, takes up a row of squares, and provides cover. A character trying to push through a hedge faces greater difficult terrain; it’s sometimes faster to Climb over.

Undergrowth

Source GM Core pg. 92 2.0
Light undergrowth is difficult terrain that allows a character to Take Cover. Heavy undergrowth is greater difficult terrain that provides cover automatically. Undergrowth in plains is usually light with a few scattered areas of heavy undergrowth, but fields of certain crops, like corn, are entirely heavy undergrowth.

Swamp

Source GM Core pg. 92 2.0
Wetlands are the most common kind of swamp, but this category also includes drier marshes such as moors. Swamps often contain quicksand hazards (page 107). Despite their soggy nature, swamps aren’t very likely to experience heavy flooding, since they act as natural sponges and absorb a great deal of water before they flood.

Bogs

Source GM Core pg. 92 2.0
Also called mires, bogs are watery areas that accumulate peat, are covered by shrubs and moss, and sometimes feature floating islands of vegetation covering deeper pools. Shallow bogs are difficult terrain for a Medium creature, and deep bogs are greater difficult terrain. If a bog is deep enough that a creature can’t reach the bottom, the creature has to Swim. Bogs are also acidic, so particularly extreme or magical bogs can be hazardous terrain.

Undergrowth

Source GM Core pg. 92 2.0
Light undergrowth is difficult terrain that allows a character to Take Cover, while heavy undergrowth is greater difficult terrain that provides cover automatically. Some sorts of undergrowth, such as thorns, are also hazardous terrain, and areas with plenty of twisting roots are uneven ground.

Urban

Source GM Core pg. 92 2.0
Urban environments include open city spaces as well as buildings. The building information in this section also applies to ruins and constructed dungeons. Depending on their construction and location, cities might be vulnerable to many sorts of disasters, especially fires and floods.

Doors, Gates, and Walls

Some of the most common obstacles that characters face in urban areas and dungeons are doors, gates, and walls.

Climbing

The table below gives the typical DC for Athletics checks to Climb a structure, which is usually a simple DC. You might adjust the difficulty based on the specifics of the structure and environment.

Demolishing

A character might want to smash their way through a door, a window, or certain walls. The Hardness, Hit Point, and Broken Threshold values provided in the table below are based on the material the structure is typically made out of, so a portcullis made of iron, for example, has a higher Hardness than one of wood. For more on damaging objects, see Player Core 269.

Strong walls, such as well-maintained masonry or hewn stone, can't be broken without dedicated work and proper tools. Getting through such walls requires downtime.

Doors, Gates, and Walls

DoorClimb DCHardness, HP (BT)
Wood2010, 40 (20)
Stone3014, 56 (28)
Reinforced wood1515, 60 (30)
Iron3018, 72 (36)
WallClimb DCHardness, HP (BT)
Crumbling masonry1510, 40 (20)
Wooden slats1510, 40 (20)
Masonry2014, 56 (28)
Hewn stone3014, 56 (28)
Iron4018, 72 (36)
PortcullisClimb DCHardness, HP (BT)
Wood1010, 40 (20)
Iron1018, 72 (36)

Forcing Open

Structures that can be opened—such as doors, gates, and windows—can be Forced Open using Athletics. This is usually necessary only if they’re locked or stuck. The DC to Force Open a structure uses the Thievery DC of its lock but adjusts it to be very hard (increasing the DC by 5). If there’s no lock, use the following table; when lifting a portcullis, use the lock DC or the DC from the table, whichever is higher.

Forcing Open

StructureForce Open DC
Stuck door or window15
Exceptionally stuck20
Lift wooden portcullis20
Lift iron portcullis30
Bend metal bars30

Crowds

Source GM Core pg. 92 2.0
Crowded thoroughfares and similar areas are difficult terrain, or greater difficult terrain if an area is truly packed with people. You might allow a character to get a crowd to part using Diplomacy, Intimidation, or Performance.

A crowd exposed to an obvious danger, like a fire or a rampaging monster, attempts to move away from the danger as quickly as possible, but it is slowed by its own mass. A fleeing crowd typically moves at the Speed of an average member each round (usually 25 feet), potentially trampling or leaving behind slower-moving members of the crowd.

Doors

Source GM Core pg. 92 2.0
Opening an unlocked door requires an Interact action (or more than one for a particularly complicated or large door). Stuck doors must be Forced Open, and locked ones require a character to Pick the Lock or Force them Open.

Floors

Source GM Core pg. 93 2.0
Wooden floors are easy to walk on, as are flagstone floors made of fitted stones. However, floors of worn flagstone often contain areas of uneven ground.

Gates

Source GM Core pg. 93 2.0
Walled settlements often have gates that the city can close for defense or open to allow travel. A typical gate consists of one portcullis at each end of a gatehouse, with murder holes in between or other protected spots from which guards can attack foes.

Guards

Source GM Core pg. 93 2.0
Most settlements of significant size have guards working in shifts to protect the settlement at all hours, patrolling the streets and guarding various posts. The size of this force varies from one guard for every 1,000 residents to a force 10 times this number.

Portcullises

Source GM Core pg. 93 2.0
A portcullis is a wooden or iron grate that descends to seal off a gate or corridor. Most are raised on ropes or chains operated by a winch, and they have locking mechanisms that keep them from being lifted easily. The rules on lifting a portcullis or bending its bars appear in the sidebar on this page. If a portcullis falls on a creature, use a slamming door trap (page 104).

Rooftops

Source GM Core pg. 93 2.0
Rooftops make for memorable ambushes, chase scenes, infiltrations, and running fights. Flat roofs are easy to move across, but they're rare in any settlement that receives significant snowfall, since heavy buildups of snow can collapse a roof. Angled roofs are uneven ground, or inclines if they're especially steep. The peak of an angled roof is a narrow surface.

Hurdling from roof to roof often requires a Long Jump, though some buildings are close enough to Leap between. A High Jump might be necessary to reach a higher roof, or a Leap followed by Grabbing an Edge and Climbing up.

Sewers

Source GM Core pg. 93 2.0
Sewers are generally 10 feet or more below street level and are equipped with ladders or other means to ascend and descend. Raised paths along the walls allow sewer workers access, while channels in the center carry the waste itself. Less sophisticated sewers, or sections those workers don’t usually access, might require wading through diseaseridden waste. Sewers can be accessed through sewer grates, which usually require 2 or more Interact actions to open.

Sewer Gas

Source GM Core pg. 93 2.0
Sewer gas often contains pockets of highly flammable gas. A pocket of sewer gas exposed to a source of flame explodes, dealing moderate environmental fire damage to creatures in the area.

Stairs

Source GM Core pg. 94 2.0
Stairs are difficult terrain for characters moving up them, and shoddy stairs might also be uneven ground. Some temples and giant-built structures have enormous stairs that are greater difficult terrain both up and down, or might require Climbing every step.

Streets

Source GM Core pg. 94 2.0
Most settlements have narrow and twisting streets that were largely established organically as the settlement grew in size. These roads are rarely more than 20 feet wide, with alleys as narrow as 5 feet. Streets are generally paved with cobblestones. If the cobblestones are in poor repair, they could be difficult terrain or uneven ground.

Particularly lawful or well-planned cities have major thoroughfares that allow wagons and merchants to reach marketplaces and other important areas in town. These need to be at least 25 feet wide to accommodate wagons moving in both directions, and they often have narrow sidewalks that allow pedestrians to avoid wagon traffic.

Walls

Source GM Core pg. 94 2.0
Well-built structures have exterior walls of brick or stonemasonry. Smaller, lower-quality, or temporary structures might have wooden walls. Interior walls tend to be less sturdy; they could be made of wooden planks, or even simply of thick, opaque paper held in a wooden frame. An underground structure might have thick walls carved out of solid rock to prevent the weight of the ground above from collapsing the structure. Rules for climbing and breaking walls are in the sidebar on page 93.

Underground

Source GM Core pg. 94 2.0
Underground environments consist of caves and natural underground areas. Artificial dungeons and ruins combine underground features with urban features like stairs and walls. Deep underground vaults have some of the same terrain features as mountains, such as chasms and cliffs. The most common disasters underground are collapses.

Dungeons

Dungeon environments, which include both ruins and contemporary buildings constructed in the wilderness, are a fairly common venue for adventures. As an environment, they combine urban features like doors and buildings (page 92) with features from an underground environment, and occasionally components from other environments. While underground dungeons are particularly common, you might also consider setting your adventure in a ruin reclaimed by the forest, with giant trees spreading their roots through the walls, or a ruin deep in a swamp, with bogs covering access to some of the ruin’s hidden secrets.

Floors

Source GM Core pg. 94 2.0
Natural underground environments rarely have flat floors, instead featuring abrupt changes in elevation that result in difficult terrain, uneven ground, and inclines.

Ledges

Source GM Core pg. 94 2.0
Ledges are narrow surfaces that overlook a lower area or provide the only means to move along the edge of a chasm. Moving across a narrow ledge requires using Acrobatics to Balance.

Rubble

Source GM Core pg. 94 2.0
Caverns can be covered in rubble, which is difficult terrain. Deep or pervasive rubble is also uneven ground.

Stalagmites and Stalactites

Source GM Core pg. 94 2.0
Stalagmites are tapering columns that rise from the floor of a cave. Areas filled with stalagmites are greater difficult terrain, and especially large stalagmites have to be sidestepped or Climbed. Stalagmites can be sharp enough they can be used as hazardous terrain in some circumstances, as can stalactites (icicle-shaped formations that hang from the roof of a cave) if they’re knocked loose from a ceiling or overhang.

Walls

Source GM Core pg. 94 2.0
Natural cave walls are rough and uneven, with nooks, crannies, and ledges. Since most caves are formed by water, cave walls are often damp, making them even more difficult to Climb.

Climate

Source GM Core pg. 95 2.0
Weather is more than just set dressing to establish mood—it has mechanical effects you can combine with environmental components to create a more memorable encounter. Weather can impose circumstance penalties on certain checks, from –1 to –4 based on severity.

Fog

Source GM Core pg. 95 2.0
Fog imposes a circumstance penalty to visual Perception checks, depending on the thickness; it causes creatures viewed through significant amounts of fog to be concealed; and it cuts off all visibility at half a mile or less—possibly much less. Conditions limiting visibility to about a mile are called mist, and those that do so to about 3 miles are called haze.

Precipitation

Source GM Core pg. 95 2.0
Precipitation includes rain as well as colder snow, sleet, and hail. Wet precipitation douses flames, and frozen precipitation can create areas of snow or ice on the ground. Drizzle or light snowfall has little mechanical effect beyond limited visibility.

Visibility

Source GM Core pg. 95 2.0
Most forms of precipitation impose circumstance penalties on visual Perception checks. Hail often is sparser but loud, instead penalizing auditory Perception checks. Especially heavy precipitation, such as a downpour of rain or heavy snow, might make creatures concealed if they’re far away.

Fatigue

Source GM Core pg. 95 2.0
Precipitation causes discomfort and fatigue. Anything heavier than drizzle or light snowfall reduces the time it takes for characters to become fatigued from overland travel to only 4 hours. Heavy precipitation can be dangerous in cold environments when characters go without protection. Soaked characters treat the temperature as one step colder (mild to severe, severe to extreme; see Temperature below).

Thunderstorms

Source GM Core pg. 95 2.0
High winds and heavy precipitation accompany many thunderstorms. There’s also a very small chance that a character might be struck by lightning during a storm. A lightning strike usually deals moderate electricity damage, or major electricity damage in a severe thunderstorm.

Temperature

Source GM Core pg. 95 2.0
Often, temperature doesn't impose enough of a mechanical effect to worry about beyond describing the clothing the characters need to wear to be comfortable. Particularly hot and cold weather can make creatures fatigued more quickly during overland travel and can cause damage if harsh enough, as shown in the Temperature Effects table below.

Appropriate cold-weather gear can negate the damage from severe cold or reduce the damage from extreme cold to that of particularly severe cold.

Table 10-13: Temperature Effects

CategoryTemperatureFatigueDamage
Incredible cold-80º F or colder (-62º C or colder)2 hoursModerate cold every minute
Extreme cold-79º F to -21º F (-61º C to -29º C)4 hoursMinor cold every 10 minutes
Severe cold-20º F to 12º F (-28º C to -11º C)4 hoursMinor cold every hour
Mild cold13º F to 32º F (-10º C to 0º C)4 hoursNone
Normal33º F to 94º F (1º C to 34º C)8 hoursNone
Mild heat95º F* to 104º F* (35º C to 40º C)4 hoursNone
Severe heat105º F* to 114º F (41º C to 45º C)4 hoursMinor fire every hour
Extreme heat115º F to 139º F (46º C to 59º C)4 hoursMinor fire every 10 minutes
Incredible heat140º F or warmer (60º C or warmer)2 hoursModerate fire every minute
* Adjust temperatures down by 15º F (9º C) in areas of high humidity

Wind

Source GM Core pg. 95 2.0
Wind imposes a circumstance penalty on auditory Perception checks depending on its strength. It also interferes with physical ranged attacks such as arrows, imposing a circumstance penalty to attack rolls involving such weapons, and potentially making attacks with them impossible in powerful windstorms. Wind snuffs out handheld flames; lanterns protect their flame from the wind, but particularly powerful winds can extinguish these as well.

Moving in Wind

Source GM Core pg. 95 2.0
Wind is difficult or greater difficult terrain when Flying. Moving in wind of sufficient strength requires a Maneuver in Flight action, and fliers are blown away on a critical failure or if they don't succeed at a minimum of one such check each round.

Even on the ground, particularly strong winds might require a creature to succeed at an Athletics check to move, knocking the creature back and prone on a critical failure. On such checks, Small creatures typically take a –1 circumstance penalty, and Tiny creatures typically take a –2 penalty.

Natural Disasters

Source GM Core pg. 95 2.0
Climate and environmental features can be a hindrance or long-term threat, but natural disasters represent acute danger, especially to those directly exposed to their fury. The damage in the following sections uses the categories in the Environmental Damage table on page 90.

Avalanches

Source GM Core pg. 96 2.0
Though the term avalanche specifically refers to a cascading flow of ice and snow down a mountain's slope, the same rules work for landslides, mudslides, and other similar disasters. Avalanches of wet snow usually travel up to 200 feet per round, though powdery snow can travel up to 10 times faster. Rockslides and mudslides are slower, sometimes even slow enough that a character might be able to outrun them.

An avalanche deals major or even massive bludgeoning damage to creatures and objects in its path. These victims are also buried under a significant mass. Creatures caught in an avalanche's path can attempt a Reflex save; if they succeed, they take only half the bludgeoning damage, and if they critically succeed, they also avoid being buried.

Burial

Source GM Core pg. 96 2.0
Buried creatures take minor bludgeoning damage each minute, and they potentially take minor cold damage if buried under an avalanche of snow. At the GM's discretion, creatures without a sufficient air pocket could also risk suffocation (Player Core 437). A buried creature is restrained and usually can't free itself.

Allies or bystanders can attempt to dig out a buried creature. Each creature digging clears roughly a 5-footby-5-foot square every 4 minutes with a successful Athletics check (or every 2 minutes on a critical success). Using shovels or other proper tools halves the time.

Blizzards

Source GM Core pg. 96 2.0
Blizzards combine cold weather, heavy snow, and strong winds. They don’t pose a single direct threat as other disasters do; instead, the combination of these factors all at once poses a substantial impediment to characters.

Collapses

Source GM Core pg. 96 2.0
Collapses and cave-ins occur when caverns or buildings fall, dumping tons of rock or other material on those caught below or inside them. Creatures under the collapse take major or massive bludgeoning damage and become buried, just as with an avalanche. Fortunately, collapses don’t spread unless they weaken the overall integrity of the area and lead to further collapses.

Earthquakes

Source GM Core pg. 96 2.0
Earthquakes often cause other natural disasters in the form of avalanches, collapses, floods, and tsunamis, but they also present unique threats such as fissures, soil liquefaction, and tremors.

Fissures

Source GM Core pg. 96 2.0
Fissures and other ground ruptures can destabilize structures, but more directly they lead to creatures taking bludgeoning damage from falling into a fissure.

Soil Liquefaction

Source GM Core pg. 96 2.0
Liquefaction occurs when granular particles shake to the point where they temporarily lose their solid form and act as liquids. When this happens to soil, it can cause creatures and even whole buildings to sink into the ground. You can use the earthquake spell for more specific rules, though that spell represents only one particular kind of localized quake.

Tremors

Source GM Core pg. 96 2.0
Tremors knock creatures prone, causing them to fall or careen into other objects, which can deal bludgeoning damage appropriate to the severity of the quake.

Floods

Source GM Core pg. 96 2.0
Though more gradual floods can damage structures and drown creatures, flash floods are similar to avalanches, except with a liquid mass instead of a solid one. Instead of burying creatures, a flash flood carries creatures and even massive objects away, buffeting the creatures and potentially drowning them. The drowning rules appear on page 437 of Player Core.

Sandstorms

Source GM Core pg. 96 2.0
Mild sandstorms and dust storms don’t present much more danger than a windy rainstorm, but they can cause damage to a creature’s lungs and spread diseases across long distances. Heavy sandstorms deal minor slashing damage each round to those exposed to the sand, force creatures to hold their breath to avoid suffocation, or both.

Tornadoes

Source GM Core pg. 96 2.0
In a tornado's path, wind conditions impose severe circumstance penalties, but creatures that would normally be blown away are instead picked up in the tornado's funnel, where they take massive bludgeoning damage from flying debris as they rise through the cone until they are eventually expelled (taking bludgeoning damage from falling).

Tornadoes usually travel around 300 feet per round (roughly 30 miles per hour). They normally travel a few miles before dissipating. Some tornadoes are stationary or travel much faster.

Tsunamis

Source GM Core pg. 96 2.0
Tsunamis present many of the same dangers as flash floods but are much larger and more destructive. Tsunami waves can reach 100 feet or more in height, wrecking buildings and creatures alike with massive bludgeoning damage from both the wave itself and debris pulled up along its path of destruction.

Volcanic Eruptions

Source GM Core pg. 97 2.0
Volcanic eruptions can contain any combination of ash, lava bombs, lava flows, pyroclastic flows, and vents.

Ash

Source GM Core pg. 97 2.0
Ash from volcanic eruptions is hot enough to cause minor fire damage each minute. It limits visibility like a thick fog and can make air unbreathable, requiring characters to hold their breath or suffocate (Player Core 437). Ash clouds generate ash lightning strikes, which typically deal moderate electricity damage but are very unlikely to hit an individual creature. Ash buildup on the ground creates areas of uneven ground, difficult terrain, or greater difficult terrain, and ash in the atmosphere can block the sun for weeks or even months, leading to colder temperatures and longer winters.

Lava Bombs

Source GM Core pg. 97 2.0
Pressure can launch lava into the air that falls as lava bombs: masses of lava that solidify as they fly and shatter on impact, dealing at least moderate bludgeoning damage and moderate fire damage.

Lava Flows

Source GM Core pg. 97 2.0
Lava flows are an iconic volcanic threat; they usually move between 5 and 60 feet per round over normal ground, so characters can often outrun them. However, flows can move up to 300 feet per round in a steep volcanic tube or channel. Lava emanates heat that deals minor fire damage even before it comes into contact with creatures, and immersion in lava deals massive fire damage each round.

Pyroclastic Flows

Source GM Core pg. 97 2.0
Mixes of hot gases and rock debris, pyroclastic flows spread much faster than lava, sometimes more than 4,000 feet per round. While cooler than the hottest lava, pyroclastic flows are capable of overwhelming entire settlements. They work like avalanches but deal half of their damage as fire damage.

Vents

Source GM Core pg. 97 2.0
Steam vents shoot from the ground, dealing moderate fire damage or more in a wide column. Acidic and poisonous gases released from beneath the surface can create wide areas of hazardous terrain that deals at least minor acid or poison damage.

Wildfires

Source GM Core pg. 97 2.0
Wildfires travel mainly along a front moving in a single direction. In a forest, the front can advance up to 70 feet per round (7 miles per hour). They can move up to twice as fast across plains due to a lack of shade and the relatively low humidity. Embers from the fire, carried by winds and rising hot air, can scatter, forming spot fires as far as 10 miles away from the main wildfire. Wildfires present three main threats: flames, heat, and smoke.

Flames

Source GM Core pg. 97 2.0
Flames are hazardous terrain, usually dealing moderate damage and potentially setting a character on fire, dealing moderate persistent fire damage. The flames from a small fire are often less dangerous than the advancing heat from the front of a large fire.

Heat

Source GM Core pg. 97 2.0
Wildfires increase the temperature in advance of the front, reaching nearly 1,500ºF at the fire’s arrival, as hot as some lava. This begins as minor fire damage every round at a reasonable distance from the front and increases to massive fire damage for someone within the wildfire.

Smoke

Source GM Core pg. 97 2.0
Wind can carry smoke far in front of the wildfire itself. Smoke imposes a circumstance penalty to visual Perception checks, depending on the thickness. It causes creatures viewed through significant amounts of smoke to be concealed, and it cuts off all visibility at half a mile or less. Near or within the wildfire, the combination of smoke and heated air require characters to hold their breath or suffocate (Player Core 437).