DESCRIPTION:
Colombia Volcanoes and Volcanics

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Select Major Volcanoes of Colombia

Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. Major explosive eruptions since the mid Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous historical eruptions since the time of the Spanish conquistadors.

Huila, the highest active volcano in Colombia, consists of an elongated N-S-trending volcanic chain mantled by a glacier icecap. The volcano was constructed within a 10-kilometer-wide caldera. Volcanism at Huila has produced six volcanic cones whose ages in general migrated from south to north. Two glacier-free lava domes lie at the southern end of the Huila volcanic complex. Only a single 16th-century explosive eruption is recorded in historical time from this little known volcano. Two persistent steam columns rise from the central peak, and hot springs are also present.

Nevado del Ruiz is a broad, glacier-covered volcano that covers more than 200 square kilometers. 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 summit caldera of an older Ruiz volcano. The 1-kilometer-wide, 240-meter-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone is located on the SW flank, and may also have been active in historical time. Steep headwalls of massive landslides cut the flanks of Nevado del Ruiz. 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.

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Armero, Colombia, destroyed by lahar on November 13, 1985.More than 23,000 people were killed in Armero when lahars (volcanic debris flows) swept down from the erupting Nevado del Ruiz volcano. When the volcano became restless in 1984, no team of volcanologists existed that could rush to the scene of such an emergency. However, less than a year later, the U. S. Geological Survey organized a team and a portable volcano observatory that could be quickly dispatched to an awakening volcano anywhere in the world.
-- USGS Photo by R. J. Janda, 1985

When the seismograph began to record the violent earth-shaking caused by yet another eruption of the Nevado del Ruiz volcano in Colombia, no one thought that a few hours later more than 23,000 people would be dead, killed by lahars (volcanic debris flows) in towns and villages several tens of kilometers away from the volcano. Before the fatal eruption the volcano was being monitored by scientists at a seismic station located 9 kilometers from the summit, and information about the volcano's activity was being sent to Colombian emergency-response coordinators who were charged with alerting the public of the danger from the active volcano. Furthermore, areas known to be in the pathways of lahars had already been identified on maps, and communities at risk had been told of their precarious locations.

Unfortunately, a storm on November 13, 1985, obscured the glacier-clad summit of Nevado del Ruiz. On that night an explosive eruption tore through the summit and spewed approximately 20 million cubic meters of hot ash and rocks across the snow-covered glacier. These materials were transported across the snow pack by avalanches of hot volcanic debris (pyroclastic flows) and fast-moving, hot, turbulent clouds of gas and ash ( pyroclastic surges). The hot pyroclastic flows and surges caused rapid melting of the snow and ice, and created large volumes of water that swept down canyons leading away from the summit. As these floods of water descended the volcano, they picked up loose debris and soil from the canyon floors and walls, growing both in volume and density, to form hot lahars. In the river valleys farther down the volcano's flanks, the lahars were as much as 40 meters thick and traveled at velocities as fast as 50 kilometers per hour. Two and a half hours after the start of the eruption one of the lahars reached Armero, 74 kilometers from the explosion crater. In a few short minutes most of the town was swept away or buried in a torrent of mud and boulders, and three quarters of the townspeople perished.

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