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Abstract:
The Young Doña Juana central vent within the Doña Juana Volcanic Complex, in SW Colombia, is an excellent example for dome-dominated, tropical arc volcanoes. Here, fast rates of weathering and erosion in the tropical climate and active tectonics across the North-Andean block strongly fragment the geological record. We focused on the geology of the Young Doña Juana central summit vent zone, which is the best exposed, the only one showing pyroclastic besides effusive activity, and has affected the inhabited territory to the west of the volcano in the XXth century. We integrate new geological mapping at a 1:5000 scale with radiocarbon ages, sedimentology analysis, and historical chronicles to reconstruct the Late Holocene evolution of this young lava-dome complex.Descriptions of new outcrops at 93 locations allowed defining lithostratigraphic units. The lithofacies associations and sedimentological analyses indicate that pyroclastic-density-currents were predominant, generated by dome collapse leading to block-and-ash flows, or by pyroclastic fountain/column-collapse producing lithic or pumice-bearing deposits. Lahars were also common. The PDCs were ~4 to 10 ´ 106 m3 in volume and deposited under granular-flow or fluid escape-dominated depositional regimes at high clast concentrations, and affecting currently inhabited areas. Hence, lava-dome growth and collapse phases, as well as lava dome/plug disruption through Vulcanian and possibly sub-Plinian eruptions dominated over the Late Holocene, with at least three main explosive eruption episodes since ~5 cal ky. We pose a new baseline of knowledge on a potentially active volcanic center of the Northern Andes experiencing explosive activity during the XX century.
