Nevado del Ruiz

Nevado del Ruiz is a stratovolcano situated in the Andes mountain range of Colombia, marking the highest point in both the Caldas and Tolima departments. Its name, "Nevado del Ruiz," translates to "Snow-covered of Ruiz," reflecting the glaciers that crown its summit. The volcano's geological history is extensive, with volcanic activity beginning approximately two million years ago. The current volcanic cone formed during the present eruptive period, which commenced about 150,000 years ago.

Geography and Geology

The volcano is a stratovolcano, composed of numerous layers of lava alternating with hardened volcanic ash and pyroclastic rocks. Its lavas are andesitic–dacitic in composition. Nevado del Ruiz is part of the Ruiz–Tolima volcanic massif, a group of five ice-capped volcanoes. The massif is located at the intersection of four active faults and lies within the Pacific Ring of Fire. The modern volcanic cone includes five lava domes constructed within the caldera of an ancestral Ruiz volcano. The volcano's summit features the Arenas crater, a large, deep depression.

Glaciers and Hydrology

The summit of Nevado del Ruiz is covered by glaciers that have generally retreated since the Last Glacial Maximum. From a peak coverage of about 1,500 km2 during the period of 28,000 to 21,000 years ago, the glaciated area has dramatically decreased. By 1959, it had reduced to 34 km2, and after the 1985 eruption, it further halved to approximately 10 km2 by 2003. The ice cap can reach depths of up to 190 meters in some areas. The meltwater from these glaciers is a crucial source of fresh water for forty surrounding towns, draining primarily into the Cauca and Magdalena Rivers.

Eruptive History and Hazards

Nevado del Ruiz typically generates Vulcanian to Plinian eruptions, which can produce swift pyroclastic flows. A significant hazard arises when these eruptions melt the mountain's snowcap, leading to massive lahars (mud and debris flows). The most devastating event occurred on November 13, 1985, when a small eruption triggered an enormous lahar that buried and destroyed the town of Armero, causing an estimated 25,000 deaths. This event, known as the Armero tragedy, is the deadliest lahar in recorded history and Colombia's worst natural disaster. Similar, though less deadly, lahars occurred in 1595 and 1845.

Current Status and Monitoring

Nevado del Ruiz continues to pose a threat to nearby communities, with estimates suggesting up to 500,000 people could be at risk from future lahars. Even small eruptions can destabilize the remaining glaciers and trigger mudflows. The volcano is constantly monitored by the Colombian Geological Survey through the Volcanic and Seismic Observatory of Manizales to provide early warnings and preparedness measures. The volcano is part of Los Nevados National Natural Park, a popular tourist destination, but its potential for destructive eruptions remains a serious concern.