Volcanoes (Under Construction)

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By Tom Verreault

Volcanoes are massively destructive setting elements available to module writers and referees. The biggest eruptions on Earth have killed tens of thousands, had lava flows stretching over a hundred kilometers, lowered global temperatures by degrees, produced acid rain that burned people, and produced mud slides and pyroclastic flows and covered huge areas with ash and debris. Volcanic eruptions wiped out communities, shifted the populations of major civilizations (Mayans), disrupted trade routes in ancient times, and in modern times have crippled world air travel and negatively impacted the world’s economy. There is tremendous scope for using them in any RPG setting.

Volcanic Eruptions as Backdrops or Setting Locations



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A Fissure Vent

This type of volcanic event erupts as a long linear fissure and can effectively be a kilometers long curtain of fire. In Iceland they are parallel to the local fault line but in Hawaii they can be radial from a volcano with a traditional caldera. One geological feature associated with narrow fissures is that they can become filled with lava, which hardens and then erosion removes the surrounding material leaving a dyke.

Both the curtains of fire and the lava dyke can be uses as blocking terrain. The lava dyke could be a clue or foreshadowing that volcanic activity is possible.

Shield Volcano

A shield volcano is formed from a low viscosity lava eruption and the lava will flow for great distance creating a volcano with a low broad shield like profile. They are not normally associated with violent eruptions but are typical on islands rather than the continental shelf. Fissure vents can be quite common with this volcano and the typical start of its eruption will be a curtain of fire from a fissure vent.

This volcano lacks the violence of an explosion but can complicate the lives of the player characters with steadily advancing flows of lava that could threaten a location or object of value to the player characters. Player characters should be able to evade the advancing lava without any problem but immovable objects or buildings in the lava’s path will eventually be destroyed. This will put time pressure on the player characters for accomplishing their mission at a location close to a shield volcano.



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Lava Dome

A lava dome is formed by high viscosity lava that will not flow very far.  They are unpredictable and can experience explosive eruptions as rock debris from the dome collapses back into the magma chamber. Pyroclastic flows may be triggered by this volcano.

Increased seismic activity from fluid pressure within the dome as well as sudden  or even steady dome growth can be used as clues and foreshadowing that an eruption is imminent. Player characters will need to be some distance from this volcano when it erupts. An associated hazard with this type of eruption is forest fires in any surrounding woodlands.



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Pyroclastic Flow

This is a fast moving (up to 700 km/hour) flow of gas and rock experiencing temperatures up to 1000 C. Pyroclastic flows have been demonstrated to flow over water as far as 48 km. Direction of the flow depends largely on the wind.

This effect is a killer if the player characters are too close. They should be tens of kilometers away and have some shelter. A prisoner on Martinique survived the 1902 eruption that killed 23,000 because of his poorly ventilated cavern like accommodations. The devastated landscape after this event becomes part of the challenge the player characters face. Trees and buildings flattened as well as the accumulation of volcanic ash.

Cinder Cone

A cinder cone volcano is what was typically portrayed by Hollywood as a volcano in film. It’s made from pyroclastic material and ejected rock and rarely does lava emerge from the summit unless early in the eruption when the lava fountains from higher gas content. As the eruption progresses the lava loses its gas content and will fill up the cone or burrow out of the base of the cinder cone and flow away from the volcano. When the eruption is done the cinder cone will be in the center of a pad of volcanic rock. Cinder cones are not uncommon on the flanks of a shield volcano.

This is the classic movie eruption though lava flowing out of the top of the cone is pure Hollywood fabrication. Like a shield volcanic eruption, this volcano can threaten an object or location of value to the player characters.


This volcano is a composite of alternating layers of lava flow and ejecta. They form steep cones with 30-35 degree slopes. The high viscosity of the lava associated with this volcano means that lava flows rarely travel very far from the volcano and the volcano is prone to pressure build up which can lead to violent eruptions. Associated hazards are mud flows, pyroclastic flows, and volcanic bombs.

The stratovolcano is the most hazardous to a civilization. Ash plumes can impact air travel and cripple a globe spanning economy. A recent eruption from this type of volcano could be used to ground air travel and interrupt launching of vehicles into space allowing a game master to limit player character movement during the time of emergency without it being too heavy handed, especially if the volcanic eruption plays more than a backdrop role in the game. This volcano is a killer and player characters will need to be some distance from it when it erupts violently.

Mud Flows

Created by water, rocky debris, and pyroclastic material, a mud flow can flow tens of meters per second, be 140 meters deep, and obliterate structures in its path travelling as far as 300 km. Its viscosity and density is that of concrete when flowing and at rest. It will typically follow a river valley.

This effect is a killer and player characters should not be directly in its path. One use for it might be that the player characters need to try to locate a location or object buried by a mud flow. For example a cargo container (suitable for the transport of goods into space) might have been swept away by a mud flow and its contents are of sufficient value to send adventurers looking for it.

Volcanic Bombs

Volcanic bombs are ejected rock from the eruption of a stratovolcano ranging from the size of a book to that of a ground car. They can travel up to 20 km. They do not actually explode by will strike a structure with such force that it explodes.

This is an excellent effect to have crashing down around the player characters if for no other reason than heightened atmosphere and increased drama. If the player character’s vehicle was struck by a small one it would be violently taken out of action or a building they are headed for could be spectacularly destroyed as they approach.


Moons made up of ice and water orbiting gas giants will experience tidal interaction from the planet they orbit. Pressure can build and fissures crack the surface ice causing plumes of volatiles like water, ammonia and methane. Radioactive decay is also believed to be a mechanism for producing this effect as well. The plume can be 2.5 to 26 km high.

In game terms it could be ruled to act as a masking screen from the Star Frontiers Knight Hawks game. In Knight Hawks the masking screen is a cloud of water sprayed out of special nozzles on the hull of a star ship and provides a measure of protection against laser weapons. A ship would need to be maneuvered to use a plume as cover from an enemy and would be quite close to the moon from which it originates.

Alternately a ship that landed “down wind” of such a plume would become coated in ice. This could become a mystery for the player characters to investigate; a strange ship encased in ice on the moon’s surface begs investigation.

Pumice Raft

A pumice raft forms from volcanic activity in the ocean and will float. These islands of rock that float can be as much as 30 km across.

In game terms it is an oddity, rock that floats, but could become a way point for characters in an aquatic adventure. Perhaps if the player character’s flying conveyance was brought down by ash in the atmosphere they may survive on the sea by climbing onto it.

Historic Catastrophic Eruptions on Earth

Vesuvius, Italy 79

Killed 25,000 and buried the city of Pompeii.

Unzen, Japan 1792

The eruption and related tsunami killed 15,000

Tambora, Indonesia 1815

This eruption cancelled summer due to the huge ash cloud blocking out sunlight. Lava and pyroclastic flows killed 10,000 and tsunamis killed another 90,000.

Krakatoa, Indonesia 1883

This eruption is estimated to have had the power of 13,000 atomic bombs. It killed 36,000 people and obliterated most of an island. Its shock wave was registered thousands of miles away.

Mt. Pelée, Martinique 1902

This eruption killed 29,000 and destroyed the city of St. Pierre. Observers off shore witnessed a mushroom cloud at the time of the eruption.

Mount St Helens, United States 1980

Killed 57 and created a 15 mile high ash plume.

El Chichon, Mexico 1982

Killed 2,000 and lowered global temperatures. Its summit now has a sulfuric acid lake.

Mt. Kilauea, United States 1983 to present.

Not the most explosive volcano but the most active with an eruption lasting 20 years.

Nevada del-Ruiz, Columbia 1985

Killed 23,000 with a mudslide amplified by the melting glaciers on its slopes.

Mt. Pinatubo, Philippines 1991

Killed 800 and spewed 2.5 cubic miles of material. Its eruption was rated as being in the Krakatoa range.

Adventure Seeds

Save the Orphans

Needy non-player characters are threatened by the imminent volcanic eruption can the player characters get them to safety in time?

Mystery of the Ice Ship

A mysterious ship is found encased in ice near a cryovolcano on a moon orbiting a gas giant. Can the player characters unravel its mysteries and recover its treasures?

A Hot Time in Alien Ruins

Steadily advancing lava flows from a shield volcano or cinder cone threatens an ancient set of alien ruins but the ruins hold the promise of great treasure. Can the player characters locate the treasure and escape before the lava arrives. For added complication include fissure vents producing fountains of fire.

Grounded by the Government

The local authorities have effectively impounded the player character’s starship soon after they land. Local scientists are predicting a major eruption and the government wants to use the player characters’ vessel to save the heads of the government. Can the player characters discover the truth and escape before volcano-geddon?