Nevado del Ruiz — snow‑capped volcano in Colombia and the Armero disaster

Physical characteristics

Nevado del Ruiz is a composite cone that combines layers of lava, ash and volcanic debris with a summit that historically has been mantled by ice. Its geology is typical of Andean stratovolcanoes formed at the subduction margin where the Nazca Plate descends beneath the South American Plate. Glacial ice on the volcano plays a central role in its hazard profile; heat from eruptions can rapidly melt snow and ice and trigger fast, water‑rich debris flows.

Notable eruptions and the 1985 disaster

Although Nevado del Ruiz has produced multiple eruptions over centuries, the most consequential in modern times occurred in November 1985. A relatively small eruption melted part of the mountain’s ice cap and generated lahars—volcanic mudflows—that traveled down river valleys. One such flow overwhelmed and buried the town of Armero, causing a very large loss of life and marking the event as one of the deadliest volcanic disasters of the 20th century.

Hazards and risk reduction

The principal hazards from Nevado del Ruiz are:

• Lahars: fast, dense flows of water, mud and rock produced by melting ice or heavy rain mobilizing loose volcanic material.
• Ashfall: fine tephra that can affect air quality, agriculture and infrastructure.
• Pyroclastic phenomena: hot flows and surges during larger explosive eruptions.

Since 1985, Colombian authorities and international partners have invested in monitoring networks, early warning systems, hazard mapping and community preparedness to reduce future losses. Land‑use planning and evacuation drills are part of ongoing efforts to limit exposure in high‑risk river valleys.

Legacy and significance

Nevado del Ruiz is widely cited in volcanology and disaster management literature as a case study in how glaciated volcanoes can produce devastating lahars and why effective communication and preparedness are essential. Locally it is sometimes referred to as the "Sleeping Lion" because of long intervals of quiescence between eruptions. The volcano remains active and monitored, serving as a reminder of the complex interactions between volcanic processes, climate (through ice), and human settlement patterns.