Report on Nevado del Ruiz (Colombia) — November 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 11 (November 1986)
Managing Editor: Lindsay McClelland.
Nevado del Ruiz (Colombia) High seismicity; temperatures increase in hot springs
Please cite this report as:
Global Volcanism Program, 1986. Report on Nevado del Ruiz (Colombia) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:11. Smithsonian Institution.
Nevado del Ruiz
4.892°N, 75.324°W; summit elev. 5279 m
All times are local (unless otherwise noted)
"Activity remained at about the same level as . . .11 October-11 November, but showed different character and location. Shallow (non-tectonic) seismic events, which increased at the end of October and early November, were more frequent than during any previous month in 1986. From measurements of station-to station amplitude ratios this high-frequency activity appeared to be W of the volcano. Low-frequency events during earlier months had been centered more to the E, suggesting a possible relationship with tectonic-type swarms in April and late October. During the same period, the frequency of shallow (explosion-type) seismic events increased. Harmonic tremor remained at low levels with occasional increases correlating with increases in shallow seismic activity.
"The crater fumarole generally emitted very small steam plumes, but some plumes reached more than 1 km when wind speeds were low. Hot springs 10 km NW of Arenas Crater showed a decrease in pH and an increase in temperature for the first time since the pre-eruption period of 1985. Ash emission was the lowest since 4 May. COSPEC measurements were infrequent due to poor weather conditions but average SO2 emissions were between 2,000 and 3,000 t/d. The latest measurement, on 10 December, was 1,700 t/d."
Geologic Background. 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: H. Meyer, INGEOMINAS, Manizales.