Report on Nevado del Ruiz (Colombia) — July 1985
Scientific Event Alert Network Bulletin, vol. 10, no. 7 (July 1985)
Managing Editor: Lindsay McClelland.
Nevado del Ruiz (Colombia) Fumarolic activity increases; ash emissions
Please cite this report as:
Global Volcanism Program, 1985. Report on Nevado del Ruiz (Colombia) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 10:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198507-351020
Nevado del Ruiz
4.892°N, 75.324°W; summit elev. 5279 m
All times are local (unless otherwise noted)
Increased thermal and seismic activity have continued. Scientists from the Central Hidroeléctrica de Caldas visited the crater on 8 July and found evidence of increased activity since their previous visit on 22 February. They reported intense noise from the fumaroles as well as increased fuming which frequently made breathing difficult. Sulfur deposits were more extensive than those noted on their previous visit. On 22 February, there had been only a thin film of sulfur covering the surface near the fumaroles, but by July sand-sized material on the inner slopes of the crater was impregnated with sulfur deposits, creating a crust 10 cm thick. A new crack was observed near the crater rim; it was 1.5 m in length, 8 cm wide, and emitted hot gas and vapors. Ground temperatures were measured at various locations as the team descended into the crater. Isotopic studies are being conducted on waters collected at thermal vents on the flanks of the volcano.
Much of the bottom of the crater was covered by a green lake that emitted hot steam from its surface. On 22 February, the lake had a pH of 0.2. The water in the lake had risen at least 1 m since February, covering a mud pool and its surrounding "mud volcano" seen on 22 February, and also nearby fumaroles. Projecting into the SE side of the lake on 8 July was a peninsula that was thought to be the remnant of these features. An unusual thaw of the glacial ice that covers much of the summit area seemed to have contributed to the rise in the water level. Further evidence for thawing came from the presence of large blocks of ice scattered near the base of the crater.
A major increase in fumarolic activity producing an enormous yellow vapor cloud was reported on 23 July.
Geological Summary. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.
Information Contacts: B. Salazar A., M. Calvache V., and N. Garciá P., Central Hidroeléctrica de Caldas.