Geophysical Hazards

Term Level Definition Source
Geophysical hazard Subgroup A hazard originating from solid earth. This term is used interchangeably with the term geological hazard. IRDR
Earthquake Type Sudden movement of a block of the Earth’s crust along a geological fault and associated ground shaking. IRDR
Ground movement Subtype Surface displacement of earthen materials due to ground shaking triggered by earthquakes or volcanic eruptions. IRDR
Tsunami Subtype A series of waves (with long wavelengths when traveling across the deep ocean) that are generated by a displacement of massive amounts of water through underwater earthquakes, volcanic eruptions, or landslides. Tsunami waves travel at very high speed across the ocean, but as they begin to reach shallow water they slow down, and the wave grows steeper. IRDR
Mass movement (dry) Type Any type of downslope movement of earth materials under hydrological dry conditions. IRDR1
Avalanche (dry) Subtype A large mass of loosened earth material, snow, or ice that slides, flows, or falls rapidly down a mountainside under the force of gravity. Debris Avalanche: The sudden and very rapid downslope movement of a mixed mass of rock and soil. There are two general types of debris avalanches. A cold debris avalanche usually results from an unstable slope suddenly collapsing whereas a hot debris avalanche results from volcanic activity leading to slope instability and collapse. IRDR
Landslide (dry) Subtype Any kind of moderate to rapid soil movement incl. lahars, mudslides, and debris flows (under dry conditions). A landslide is the movement of soil or rock controlled by gravity and the speed of the movement usually ranges between slow and rapid, but it is not very slow. It can be superficial or deep, but the materials must make up a mass that is a portion of the slope or the slope itself. The movement has to be downward and outward with a free face. EM-DAT
Rockfall (dry) Subtype
Sudden subsidence (dry) Subtype Sinking of the ground due to groundwater removal, mining, dissolution of limestone (e.g., karst sinkholes), extraction of natural gas, and earthquakes. In this case, the sinking occurs under dry conditions as a result of a geophysical trigger. IRDR2
Volcanic activity Type Subtype (General) A type of volcanic event near an opening/vent in the Earth’s surface including volcanic eruptions of lava, ash, hot vapor, gas, and pyroclastic material. IRDR
Ash fall Subtype Fine (less than 4 mm in diameter) unconsolidated volcanic debris blown into the atmosphere during an eruption; can remain airborne for long periods of time and travel a considerable distance from the source. IRDR
Lava flow Subtype The ejected magma that moves as a liquid mass downslope from a volcano during an eruption. IRDR
Pyroclastic flow Subtype Extremely hot gases, ash, and other materials with a temperature of more than 1,000 degrees Celsius that rapidly flow down the flank of a volcano (at more than 700 km/h) during an eruption. IRDR
Lahar Subtype Hot or cold mixture of earthen material flowing down the slope of a volcano either during or between volcanic eruptions. IRDR

  1. The definition of “Mass movement (dry)” is adapted from the “Mass movement” IRDR definition. ↩︎

  2. The first definition sentence of “Sudden subsidence (dry)” is the definition of “Subsidence” in the IRDR glossary. The second sentence has been added to distinguish this class from “Sudden subsidence (wet)” in the hydrological group. ↩︎