Quaternary eruptive history of Nevado del Ruiz (Colombia)

Abstract

Nevado del Ruiz has a 1.8-m.y.-long eruptive record that includes alternate construction and destruction of three edifices during three main eruptive periods, termed “ancestral Ruiz”, “older Ruiz” and “Ruiz”. Nevado del Ruiz is located on a complex intersection of four groups of faults, the most significant being the N20° E Palestina strike-slip fault and the N50° W Villamaria-Termales normal fault. Ancestral Ruiz was a broad stratovolcano built by two eruptive stages of lava flows starting about 1.8 Ma ago and ending 1.0 Ma ago. A partial collapse and formation of a caldera are thought to have occurred between 1.0 and 0.8 Ma ago. Older Ruiz was a stratovolcano constructed by lava flows in three stages starting about 0.8 Ma ago and ending about 0.2 Ma ago. Extensive and voluminous welded and nonwelded pyroclastic-flow deposits that partly fill preexisting valleys record the formation of a young summit caldera between 0.2 and 0.15 Ma ago. Present Ruiz is formed by a cluster of composite lava domes that probably filled the summit caldera of older Ruiz. Present Ruiz eruptive activity is mostly explosive, but also includes dome growth, and parasitic dome activity of La Olleta and Alto La Piramide. Twelve eruptive stages occurred during the last 11,000 years, accompanied by rockslide-debris avalanches, pyroclastic flows or surges, and their subsequent interactions with the ice cap, as well as by glacial erosion and mass-wasting. Diverse processes within these twelve stages have led to a partial destruction of the summit domes. This long and complex Pleistocene and Holocene eruptive sequence helps to put the November 13, 1985, eruption into a broader perspective.