frequently over recorded history. Significant eruptions occurred in or around 1580, 1616, 1797, 1830, 1865-1869, 1891, and 1936. With a record like this, one always has to keep the possibility of an eruption in mind, especially with a fair-size city so close by.
Galeras is also dangerous on account of the type of magma (molten volcanic rock) that it produces. Known as ‘andesite’, Galeras’s magma is rich in silica and consequently is thick and pasty, especially after it is exuded onto the surface and has a chance to cool. Unlike the more liquid magmas found in Hawaiian volcanoes, which run smoothly down the volcanoes’ outer slopes as incandescent lava flows, the magma at Galeras tends to pile up where it erupts, forming solid domes of lava that eventually seal off the vents through which the magma reached the surface. Thus, if pressure continues to build as more magma is forced upward from below, the result may be a sudden and difficult-to-predict explosion.
Frequent, explosive eruptions are dangerous, but there are also factors that tend to lessen the hazards posed by Galeras. For one thing, the historical eruptions have been fairly small – most of them have been confined to the volcano’s caldera, the mile-wide sunken amphitheatre that was created when the volcano’s summit collapsed during some prehistoric eruption. Also, the occasional lava flows and pyroclastic flows – lethal surges of ash and pumice buoyed by hot gases – have generally exited the caldera toward the west, because the caldera’s walls have been breached on that side. The city of Pasto, on the eastern side of the volcano, is partially protected by the caldera’s 500ft rampart.
One more feature of Galeras limits the hazard it poses to the local population. Because of its moderate altitude, combined with its location barely 80 miles north of the equator, its summit is free of snow or ice. Snow banks or glaciers may enhance a volcano’s beauty, but they also spell danger because an eruption can rapidly melt the ice. The resulting meltwater, mixed with soil, rock, and ash, is likely to rush downhill in the form of all-consuming mudflows. In 1985, an eruption of the 17,400ft Nevado del Ruiz volcano, 300 miles northeast of Galeras, melted its glacial cap: the resulting mudflow travelled more than 20 miles to the town of Armero, which was nearly totally destroyed at a cost of more than 23,000 lives. Such an event could not happen at Galeras.
Whatever its danger level, Galeras was largely ignored by the world’s volcanologists until 1988. In that year, after half a century of inactivity, the volcano showed renewed signs of life. A series of small earthquakes struck the area. In addition, steam began to vent from the volcano. The Colombian government, hypersensitive to volcanic hazards after the Nevado del Ruiz tragedy, sent several volcanologists to investigate and monitor the situation.
Climbing Galeras is a simple matter: one gets into a jeep and drives up. The access road zigzags its way up to the south-eastern rim of the caldera. There, in 1988, was located a small police post and several communications towers. A few policemen were always stationed at the post to guard the towers against sabotage by the leftist guerrillas who were active in Nariño province. From the rim, one could look down on the interior of the caldera: its main feature was a central volcanic cone. About half a mile wide at its base, the cone rose 450ft from the floor of the caldera but did not rise as high as the caldera rim. At the top of the cone was the actual crater of the volcano – a 100ft-deep cavity. Getting from the caldera rim to the edge of the crater was an arduous journey: it involved edging down the very steep eastern rampart of the caldera with the aid of a fixed rope, crossing the floor of the caldera (the ‘moat’), and then climbing the cone. From there, it was another tricky descent into the crater itself.
When the Colombian volcanologists
Galeras is also dangerous on account of the type of magma (molten volcanic rock) that it produces. Known as ‘andesite’, Galeras’s magma is rich in silica and consequently is thick and pasty, especially after it is exuded onto the surface and has a chance to cool. Unlike the more liquid magmas found in Hawaiian volcanoes, which run smoothly down the volcanoes’ outer slopes as incandescent lava flows, the magma at Galeras tends to pile up where it erupts, forming solid domes of lava that eventually seal off the vents through which the magma reached the surface. Thus, if pressure continues to build as more magma is forced upward from below, the result may be a sudden and difficult-to-predict explosion.
Frequent, explosive eruptions are dangerous, but there are also factors that tend to lessen the hazards posed by Galeras. For one thing, the historical eruptions have been fairly small – most of them have been confined to the volcano’s caldera, the mile-wide sunken amphitheatre that was created when the volcano’s summit collapsed during some prehistoric eruption. Also, the occasional lava flows and pyroclastic flows – lethal surges of ash and pumice buoyed by hot gases – have generally exited the caldera toward the west, because the caldera’s walls have been breached on that side. The city of Pasto, on the eastern side of the volcano, is partially protected by the caldera’s 500ft rampart.
One more feature of Galeras limits the hazard it poses to the local population. Because of its moderate altitude, combined with its location barely 80 miles north of the equator, its summit is free of snow or ice. Snow banks or glaciers may enhance a volcano’s beauty, but they also spell danger because an eruption can rapidly melt the ice. The resulting meltwater, mixed with soil, rock, and ash, is likely to rush downhill in the form of all-consuming mudflows. In 1985, an eruption of the 17,400ft Nevado del Ruiz volcano, 300 miles northeast of Galeras, melted its glacial cap: the resulting mudflow travelled more than 20 miles to the town of Armero, which was nearly totally destroyed at a cost of more than 23,000 lives. Such an event could not happen at Galeras.
Whatever its danger level, Galeras was largely ignored by the world’s volcanologists until 1988. In that year, after half a century of inactivity, the volcano showed renewed signs of life. A series of small earthquakes struck the area. In addition, steam began to vent from the volcano. The Colombian government, hypersensitive to volcanic hazards after the Nevado del Ruiz tragedy, sent several volcanologists to investigate and monitor the situation.
Climbing Galeras is a simple matter: one gets into a jeep and drives up. The access road zigzags its way up to the south-eastern rim of the caldera. There, in 1988, was located a small police post and several communications towers. A few policemen were always stationed at the post to guard the towers against sabotage by the leftist guerrillas who were active in Nariño province. From the rim, one could look down on the interior of the caldera: its main feature was a central volcanic cone. About half a mile wide at its base, the cone rose 450ft from the floor of the caldera but did not rise as high as the caldera rim. At the top of the cone was the actual crater of the volcano – a 100ft-deep cavity. Getting from the caldera rim to the edge of the crater was an arduous journey: it involved edging down the very steep eastern rampart of the caldera with the aid of a fixed rope, crossing the floor of the caldera (the ‘moat’), and then climbing the cone. From there, it was another tricky descent into the crater itself.
When the Colombian volcanologists
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