Chapter 10. Galeras (Colombia)

Here is volcanic threat — summed up in a single image!

That is the city of San Juan de Pasto on the right. It’s the capital of Nariño Department, in the Colombian Andes, and home to alnost half a million people.

Another 80,000-90,000 live in those small towns and other land holdings in the countryside around Pasto. (Calvache and Duque-Trujillo; Cardona; Muñoz et al.)

And there on the left, roughly six miles west of Pasto, is the volcano — a Vesuvius/Avachinsky-style active cone (labeled “Galeras”) that is surrounded on three sides by the somma walls of an older collapsed fire mountain. (Calvache and Duque-Trujillo; Williams and Montaigne)

Like Vesuvius and Avachinsky, the Galeras cone occasionally has powerful blasts — at least six of them in the last 4,500 years — as well as many small to moderate vulcanian events. (Cardona; GVP; Muñoz et al.)

All these ancient eruptions have smoothed out the rugged mountain topography with up to a hundred feet or more of ashfall and pyroclastic flow deposits (Calvache and Duque-Trujillo; Muñoz et al.), creating a nice level surface of rich soil on which to build cities and farms, as well as to construct a ring highway around the volcano’s base.

As you can see, people are thriving here today.

Five-hundred-year-old Pasto sits atop ancient pyroclastic flow deposits erupted from Galeras’ granddaddy — Jenoy — more than 45,000 years ago.

What’s left of old Jenoy Volcano isn’t considered a threat any more. But Galeras is.

Thousands of people now live and work on cooled pyroclastic flows that Galeras — Colombia’s most active volcano — has belched out during the last two millennia.

That’s hardly any geologic time at all, which means that Galeras will likely hit at least some of these places again.

However, enough time has passed for many locals to have developed a belief that the volcano, if shown respect and left undisturbed, will never harm them.

Seeing volcanic hazard through a satellite image is one thing. Communicating that hazard to local people who have a ground-based, traditional view of the volcano as a benign neighbor is something else entirely.

When science and the popular imagination meet, it can be like combining chocolate and peanut butter: for instance, the Victorian public’s fascination with dinosaurs not only brought us, indirectly, such delights as Jurassic Park — it also focused money and manpower on the then-new field of paleontology and associated scientific disciplines: an investment that is still paying dividends today.

But sometimes the meeting of geoscience and public perception seems more like a traffic accident.

That is my impression of efforts to manage volcanic risk at Galeras, as described in detail by Cardona.

But no one gave it up as an impossible task.

Today, lines of two-way communication are open. Many people are working hard to ensure that this particular meeting of the minds will ultimately benefit both scientists and the local people whose lives and property are at risk here. (Mesías Rosas; Wilmshurst)

And the lessons learned here are being incorporated into volcanic hazard communication worldwide.

What is Galeras?

It is a composite cone — the currently active part of a larger volcanic complex that owes its existence to an intricate subduction zone setting underneath the Colombian Andes. (Calvache and Duque-Trujillo)

This Galeras Volcanic Complex, more than a million years in the making, formed in stages with a series of vents that shifted eastward, under tectonic control, to the present cone location. (Calvache and Duque-Trujillo; Ugalde et al.)

For most of that time, the complex mainly erupted lava, building up some tall volcanoes. It’s only in the last 10,000 years or so that Galeras has developed its current style of frequent, typically small explosions. (Ugalde et al.)

There were two caldera-forming eruptions here in the late Pleistocene, as well as at least three Rainier-style sector collapses due to hydrothermal alteration of the rock. (GVP; Monsalve-Bustamante; Ugalde et al.)

The next-to-last collapse was of Jenoy Volcano — Galeras’ granddaddy — tens of thousands of years ago.

Next came Urcunina, which grew to an estimated 15,000 feet before losing its summit and western flank in a giant debris slide some time between 12,000 and 5,000 years ago.

Then, about 4,500 years ago, the Galeras cone appeared at the top of its daddy’s horseshoe-shaped collapse scar, which was and still is open to the west.

These climbers hiked up the Urcunina wall to see dawn from the top. The steaming Galeras cone isn’t well lit here but you can get some idea of its size. They also caught the eruptive plume from nearby Reventador over in Ecuador.

That cone isn’t yet large enough to rise above the truncated eastern flank of Urcunina (which is what people can see from Pasto and usually call “Galeras.”)

This footage of a 2008 vulcanian blast at Galeras, recorded on a monitoring camera in Pasto, shows how easy it is to mistake Urcunina’s flank for the active volcano just behind it.

Almost all of this information has been collected during the last three decades or so.

It wasn’t available in 1989, when Galeras first stirred after several decades of slumber.

That lack of knowledge, along with social and political repercussion from the country’s volcano disaster at Armero a few years earlier, contributed to the serious difficulties scientists and emergency managers encountered during the crisis. (Cardona)

Galeras and the Decade Volcano program

Colombia has many active volcanoes: 14, per the Global Volcanism Program, and up to 25 according to Monsalve-Bustamante (Table 1).

People have coexisted with these fire mountains for centuries, and no systematic study of the volcanoes was done until more than 20,000 residents of the town of Armero were buried by a mudflow during the 1985 eruption of Nevado del Ruiz Volcano — the result of cumulative human error that kept them in their homes when they could have escaped simply by walking to higher ground nearby. (Monsalve-Bustamente; Ugalde et al.; Wilmshurst)

After that disaster, the national officials charged with risk reduction and disaster management (DN-PAD) requested evaluation of all active Colombian volcanoes through INGEOMINAS — the country’s geological hazard specialists. (Cardona)

INGEOMINAS got to Galeras in 1988, and in February 1989, that volcano began to wake up. The survey responded by bringing in more instruments and setting up regular monitoring through an observatory in Pasto. (Cardona)

At the same time, DN-PAD coordinated activities of various national, regional, and local preparedness groups and invited international experts for consultations with INGEOMINAS and local emergency committees. (Cardona)

And in 1991, Galeras was selected as a Decade Volcano.

Unfortunately, little was known about Galeras at that point; volcanologists could not be certain about the size of the impending eruption. (Spoiler: It was a VEI 2, per the GVP.) (Cardona)

Hanging over everyone’s head was the shadow of that recent tragedy at Nevado del Ruiz.

Per Cardona:

[Galeras] volcano’s activity increased significantly during March and April until the first eruptive crisis during May 4-9, 1989. At this point, a large national, regional and local mobilization began, prompted by fear of a possible great disaster. This fear was based on memories of the relatively recent events at Nevado del Ruiz volcano in 1985, where approximately 22,000 deaths and 2500 injuries occurred as a result of lahars from the snow-covered volcano…Although effective inter-institutional cooperative work had been accomplished, some unfortunate events in 1989 generated strong dissatisfaction within economic organizations and the population as a whole.

These included, but weren’t limited to, unilateral declarations of voluntary evacuation and alert level changes that scared people and caused confusion and other problems. Worse, the media sensationalized it, exaggerating the seriousness of events at Galeras. (Cardona)

This all led to a reversal in political support for volcanic hazard management, especially at the regional and local levels. (Cardona)

For example, mayors and province governors refused to attend the Decade Volcano workshop in 1993 despite one of its goals being better relationships between scientists and local officials and residents. (Muñoz et al.)

Things reached their lowest point when the deaths of six volcanologists and three tourists in an explosion that occurred during a workshop field trip in Galeras crater on January 14, 1993, led to a confrontation between regional and national authorities, per Cardona.

Still, the Decade Volcano studies brought new information about the role played in volcanism by near-surface gas. (Newhall, 1999)

The workshop ended with a call for detailed mapping of the Galeras Volcanic Complex; improved monitoring by the Pasto Observatory; more training of Colombian volcanologists; and establishment of an effective hazards assessment and public education program for those living on or near the volcano. (Muñoz et al.)

A problem has grown out of that last point.

Hazard assessment led to the official decision to relocate communities sitting in zones at high risk of pyroclastic flows — the chief hazard at Galeras. (Hurtado Artunduaga and Cortés Jiménez; Wilmshurst)

To the surprise of scientists and hazard managers, people living in those communities are resisting the move. (Wilmshurst)

Wilmshurst goes into detail on this. Basically, she notes that some efforts in 2009 opened up a dialogue between residents who have “other considerations alongside the protection of life” and those who are trying to save as many lives as possible in a future Galeras eruption.

I can’t translate what these Jenoy indigenous people, living on the volcano’s flanks, are saying; however, the 2013 video’s title is “Jenoy Without Fear.”

But, at least as of 2011, the stalemate continued. (Mesías Rosas)

And Galeras is restless as it sleeps.


Location: 1.22° N, 77.37° W, Narino Department, Colombia. The GVP Volcano Number is 351080.

Nearby Population:
Per the Global Volcanism Program (GVP) website:

  • Within 5 km (3 miles): 705.
  • Within 10 km (6 miles): 120,817.
  • Within 30 km (19 miles): 630,777.
  • Within 100 km (62 miles): 1,700,248.

Current Status:

Yellow, Phase III, change in behavior.


  • Eruption styles: Galeras has had cycles of moderately explosive activity, with a few powerful (VEI 3 to 4) eruptions over the last 6,000 years or so.
  • Biggest recorded event: In 1866, the volcano sent a 90-foot-thick wall of lava almost four miles long down its western flank towards the town of Consaca, which was unharmed.
  • Most recent eruption: 2014.


Current information about all Colombian volcanoes, including Galeras, is online at the Colombian Geological Service website (Spanish). Galeras is monitored through the Pasto Volcano Observatory.

The Washington Volcanic Ash Advisory Center (VAAC) issues aviation advisories as needed. At the time of writing, none are in effect for Galeras.

This is one of the Decade Volcano eBook chapters that had to be completely rewritten. I decided to share it now for that reason and also because of the ongoing stalemate (as far as I can tell from the outside looking in) on the resettlement issue.

Featured image: NASA


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