Decade Volcano: Galeras

What you’re looking at here is a parent-child portrait done in igneous rock.

While everyone refers to the whole thing as “Galeras,” this is technically only the name of that 5,000-year-old smoking volcanic cone.

Those enveloping walls of rock around it are all that’s left of the cone’s daddy — Urcunina, an active volcano from roughly 18,000 to 5,000 years ago.

Urcunina may have been 15,000 feet tall when it collapsed in a huge debris slide that traveled westward.

The collapse scar is most easily seen from space. (Image: NASA/JPL)

In this radar image taken during one of the Space Shuttle missions, that reddish area filling a valley east of Galeras is the city of San Juan de Pasto.

It is a regional government center and home to about 300,000 people.

The Galeras family of volcanoes has even more members, though these don’t have much of a presence today.

For example, Pasto sits atop ancient pyroclastic flow deposits erupted from Galeras’ grandfather, Jenoy, more than 45,000 years ago.

Jenoy Volcano and its even older relatives aren’t considered threats today.

Galeras is, though.

It’s Colombia’s most active volcano and many people live nearby. Pasto is growing, while new farms and settlements have been established, some on the volcano’s slopes.

Today, a village called Jenoy is built on pyroclastic flows from an 1830 Galeras eruption.

Indeed, per Williams and Gresham, thousands of people now live and work on cooled pyroclastic flows that Galeras has belched out during the last two millennia.

That’s hardly any geologic time at all, but it’s long enough for many locals to have developed a belief that the volcano, if shown respect and left undisturbed, will never harm them.

They feel that the eruptions are more spectacle than deadly hazard.

And many certainly are:

The remaining walls of old Urcunina block the view of Galeras cone from Pasto.

But volcanologists recognize the hazards here.

Galeras awoke in 1988 after sleeping through the mid-20th century. Given its closeness to a large population center, as well as the fact that very little was known about this frequent erupter, Galeras was made one of the Decade Volcanoes.

Galeras is the only Decade Volcano besides Unzen to have killed experts who were studying it during the International Decade declared in part to mitigate volcanic risk.

In early 1993, volcanologists convened an international workshop in Pasto. On January 14th, some of them took a field trip onto the volcano, which had seemed to quiet down a lot after a big explosion in mid-1992.

During the day, a few of these experts even ventured close to the cone to collect gas samples and take geophysical readings. They needed this data to learn more about the volcano’s inner structure and processes.

Such knowledge is necessary when making plans to protect human lives and property.

Unfortunately for them, Galeras wasn’t really quiet. Its conduit was plugged and pressure had been building inside since 1992.

The blast came just as scientists were starting to leave the crater. Six volcanologists and three civilians who had come up out of curiosity died instantly; several other group members were injured.

Once again, we laypeople see that even knowledgeable people are not safe on active volcanoes. They take calculated risks — and have lost their gamble with the fire mountain at least 67 times between 1893 and 2006. (Brown et al)

We have no business being on an active volcano at all.

Decade Volcano studies at Galeras did give volcanologists better insight into this volcano’s eruptive history, as well as showing the significance of seismological signals called tornillos in terms of forecasting activity (though more needs to be learned about these and other possible eruption precursors).


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

Nearby Population:

Per the Global Volcanism Program 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. The most recent reports found online are of increased seismicity in 2018, including M4 earthquakes that caused damage, as well as landslides in nearby communities. Two people died when their house was crushed by falling rocks.


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