Evolution of the Galeras Volcanic complex, SW Colombia: An updated version of the stratigraphy and geological map

Abstract

The Galeras Volcanic Complex (GVC) is one of the most active centers in the southern Colombian Andes. In this study, we present an updated version of the GVC geological map by integrating field observations with existing literature, new Ar/Ar and ¹⁴C geochronology, petrography, geochemistry, and remote sensing analyses. Our revised stratigraphic scheme combines lithostratigraphic units (as the basic mapped units) into informal lithosomes (representing the main eruptive centers), with interpretations of the volcanological sequence in terms of eruption units (e.g., fallout, pyroclastic density current, block-and-ash flow) and volcanic activity units (e.g., period, epoch, eruption, phase, pulse), which are fundamental for understanding the volcanic evolution of the GVC throughout its history.

The GVC is an andesitic to basaltic andesitic volcanic complex consisting of five overlapping stratovolcanoes: Cariaco, Coba Negra, Genoy, Urcunina, and Galeras; as well as one adventive cone known as La Guaca located southwest of the complex. Only remnants of the oldest Cariaco edifice, formed between 1440 ± 163 and 1249 ± 279 ka, are preserved to the west. Progressive vent migration eastward led to the formation of the Coba Negra (1138 ± 30 ka – 406 ± 3.2 ka) and Genoy (364 ± 47 ka to ∼9 ka) structures, controlled by lateral collapses under structural influence. Monogenetic activity southwest of the complex is recorded by basaltic lava flows dated at 900 ka and 185 ka, as well as the La Guaca scoria cone. Urcunina, smaller than the previous edifices, was the last eruptive center (∼7.5–0.9 ka) before the current active cone. Similar to Coba Negra and Genoy, the summit of Urcunina is truncated by a volcano-tectonic collapse scar, representing a proximal unconformity that, along with its related disconformities in medial to distal zones, indicates volcanic quiescence. Renewed eruptions occurred in approximately the same vent position, filling the upper part of the Urcunina tectonic depression and forming the active Galeras cone. Holocene activity has been dominated by dome-building events, lava flows, Strombolian activity, and minor to moderate vulcanian eruptions, often destroying domes partially or completely. Deposits from historical eruptions are primarily found around the summit and upper parts of the Urcunina collapsed scar. The volcano is considered active based on current seismic activity, gas emissions through fumaroles, hot springs, and the eruptive activity recorded from 1989 to 2013.