Why this glacier-capped Colombian volcano remains one of the world's most dangerous peaks
In short: Nevado del Ruiz is a massive stratovolcano in central Colombia, famous for its deadly history of lahars. While it remains active today, its greatest threat lies in its summit icecap. When eruptions melt this snow, the resulting mudflows can devastate entire towns, as seen in the tragic events of 1985.
Nevado del Ruiz is a sprawling stratovolcano covering over 200 square kilometers in the Colombian Andes. It is built from successive layers of andesitic and dacitic lavas, ash, and pyroclastic deposits. The summit features the Arenas crater, a 1-kilometer-wide and 240-meter-deep feature surrounded by glaciers. These glaciers are a defining characteristic of the mountain, which is part of the Ruiz-Tolima volcanic massif. The volcano sits above the boundary where the Nazca Plate subducts beneath the South American Plate, a tectonic setting that fuels its explosive potential.
The volcano's most infamous moment occurred on November 13, 1985, when an explosive eruption at the Arenas crater triggered massive lahars. These mud and debris flows surged down river valleys, burying the town of Armero and causing at least 23,000 deaths. This disaster remains the deadliest eruption in South American history. The mechanism is terrifyingly efficient: the heat from eruptive material rapidly melts the summit's ice and snow, creating a deluge of water that mixes with volcanic debris to form high-speed, destructive flows that can travel tens of kilometers from the source.
Today, the volcano is under constant surveillance by the Servicio Geológico Colombiano. Monitoring efforts include tracking seismic activity, sulfur dioxide emissions, and thermal anomalies. Recent reports from 2024 and 2026 highlight ongoing intermittent gas-and-ash plumes, ashfall, and fluctuating seismicity. While the current alert level is set to Yellow, the threat persists for the estimated 500,000 people living in surrounding areas. The glaciers, which have significantly retreated since the 1985 eruption, continue to pose a risk, as any future explosive activity could again mobilize the remaining ice into dangerous lahars, underscoring why this peak remains a critical focus for geological study and public safety.
The mountain's history is long, with eruptive activity beginning in the Pleistocene. Historical records of eruptions date back to 1570, and the current eruptive period has been ongoing since November 2014. Beyond the summit, the volcano features other structures like the La Olleta pyroclastic cone, which may have been active in historical times. The combination of its complex tectonic position, its persistent volcanic activity, and the presence of a vulnerable icecap makes Nevado del Ruiz a subject of both scientific fascination and significant humanitarian concern.
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Sources
- Summary by Intellect · source: Global Volcanism Program | Nevado del Ruiz
- Also: Nevado del Ruiz Volcano, Colombia - NASA Science
- Also: Nevado del Ruiz
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