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Pyroclastic deposits of San Diego maar, central Colombia: an example of a silicic magma-related monogenetic eruption in a hard substrate

Abstract The San Diego maar is a volcano located at the middle of the Colombian Central Cordillera that forms part of the dispersed and isolated Samaná Volcanic Field (with at least three volcanoes). San Diego is excavated on Triassic metamorphic rocks and Neogene sub-volcanic andesitic units, and forms approximately 15 m of mostly unconsolidated eruption-related deposits. These deposits were divided into four stratigraphic units (U1–U4) that together define the evolution of the eruption: (1) an unsteady vent-clearing stage; (2) drier to wet pyroclastic base surges; (3) dry base surges; and (4) a final wet stage. At the end of the activity, the crater was enlarged due to a complex set of rock falls and slides in the crater walls. Finally, the volcanic activity switched to a magmatic phase, creating a dacitic dome. The northern dome flank was affected by a gravitational collapse that produced a small-volume debris avalanche. The eruption style of the San Diego maar was controlled by the stratigraphic, structural and hydrogeological characteristics of the substrate, as well as the surficial environmental condition. In addition, the mountainous terrain around the maar crater controlled the deposit extension. These constraints provide additional information for a hazard assessment related to this type of eruption in the region.