Geologic Background:
In the Andes 150 km WNW of Bogota, Ruiz is the
northernmost and highest Colombian volcano with historic
activity. Nevado del Ruiz, located 33 km SE of Manizales,
is a broad stratovolcano of andesitic and dacitic lavas
and andesitic pyroclastic deposits that cover more than
200 km2. Steep headwalls of massive landslides cut its
flanks, and melting of its summit ice cap during
historical eruptions resulted in devastating lahars. The
last eruption began with moderate phreatic ejections on
11 September 1985. On 13 November 1985 an explosive
eruption produced pyroclastic flows and surges that
melted part of the summit ice cap. Major mudflows
subsequently devastated Armero and other towns on the
flanks of the volcano, causing over 23,000 fatalities.
Intermittent minor ash emissions with occasional stronger
phreato-magmatic eruptions continued until July 1991.
Historic Activity:
- Eruptions in 1595, 1822, 1829, 1831, 1833, and
1845.
- Its first major historic eruption, in 1595, caused
damaging mudflows and those of 1845 resulted in
fatalities presaging the tragic events of 1985.
Recent Activity:
- Increased seismic activity began in November
1984.
- Minor phreatic activity in early 1985 along with
seismic activity. Small eruption on September 11, 1985
generated moderate mudflow which advanced 27 km to the
NE. Continued minor phreatic activity and steam emissions
into November.
- Volcanic tremor begins on November 10 and major
eruption occurs on November 13, 1985 generating mudflows
which kill 20,000 people. Several days of eruptive
activity.
- Phreatomagmatic eruption in early September resulted
in mudflow. Ash was emitted on 7 days during May 1990 and
on 5 days in July.
- Tremor was continuing in January thru March 1991 with
associated ash emissions through July.
- A high-frequency earthquake swarm in mid-March and
early April 1994, ended nearly two years of low activity.
Additional earthquake swarms occurred in July-Sept.
1995.
- Earthquake swarms in Jan.-June1996. A new fumarolic
field and a hot spring were found 1.7 km NE of Arenas
Crater at an elevation of 4,628 m.
Data Sources
- Smithsonian's SEAN Bulletin (V. 10, No. 5 to V. 14,
No. 12)
- Global Volcanism Network (V. 15, No. 1 to V. 24, No.
4).
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