Third version of the hazard map of Galeras Volcano, Colombia

Galeras is an andesitic stratovolcano whose activity is generally characterized by vulcanian eruptions. Based on14C dating, the active cone is considered to be 5000 years old. During that time, six major periods of eruptive activity have been identified, together with 45 individual events of pyroclastic flows, tephra falls, lava flows and lahars, excluding those reported in historic time ( < 500 years) and those which have occurred since the first signs of the current activity (1988). The stratigraphy of the past 5000 years reveals that the most common events are pyroclastic flows, constituting the principal volcanic hazard of Galeras. Additionally, lava extrusion, tephra falls, and lahars have also occurred, but are lesser hazards. The two previous hazard maps of Galeras did not account for the studies mentioned above. Methodology for this revision of the volcanic hazard map of Galeras is based on (1) probabilistic zoning of phenomena associated with eruptions that have occurred during the past 5000 years and (2) modeling of other phenomena which did not appear in the geologic record, such as shock waves and ballistic projectiles. The map consists of three categories of hazard zones: high, medium and low. The zone of high hazard is defined principally by the distribution of pyroclastic flow deposits, while the zone of low hazard is defined by tephra fall deposits. The medium hazard is a transition zone and ideally, if based on the geological record, does not include pyroclastic flows; however, it is possible that a comparatively large pyroclastic flow could extend into this zone. Additionally, this zone defines the possible trajectories of secondary lahars.