Who will be affected if Nevado del Ruiz volcano erupts after 38 years?

The Nevado del Ruiz volcano in Colombia, known for its deadly eruption 38 years ago that claimed 25,000 lives, is exhibiting seismic activity once again. Because it is located in the highly dangerous Pacific Ring of Fire, authorities issued a warning on Friday about a "probable" eruption in a matter of days or weeks.

High threat exposure for 57,000 people

According to an evaluation by the Colombian Geological Service, there are 57,000 people exposed to a high threat if the Nevado del Ruiz volcano erupts. More than 42,000 of them are dispersed rural populations, while the rest live in municipal capitals and populated centers.

That number of people, in municipalities such as Villamaría (Caldas), Casabianca, Herveo, Murillo and Villahermosa (Tolima), refers to the number of inhabitants that would have to be evacuated from the area in the event of an eruption.

Colombian official comments on volcano threats

Julio Fierro, director of the Colombian Geological Service, recalled that, although there is an orange alert, it may change in the coming days, depending on more intense or mild conditions. That is, it is not a certainty that the alert changes to be red, but it can also 'go down' and become yellow. 

“There is a probability that there will be an eruption, not a certainty, we are going to follow it. Our responsibility is to continue monitoring and generate daily reports, because we cannot predict what will happen," Fierro said. 

Threat events that could occur include pyroclastic flows, shock waves, debris avalanches, or volcanic gases, among others. 

He added that changes in seismicity, in terms of magnitude and depth, will determine whether an evacuation is ordered. For example, if there are more earthquakes and they are getting closer to the surface, the decision could be made.

Increase in seismic activity at Nevado del Ruiz

Since March 24, there has been an increase in seismic activity associated with a fracturing of rock inside the volcano. This seismicity is located on the southwestern flank of the volcano at a distance from 2 to 5 km from the Arenas crater, at depths between 2 and 4 km from the top of the volcano.

John Makario, Technical Director of Geothreats of the SGC explained that the most probable hypothesis is that it is due to an intrusion process inside the Nevado del Ruiz. 

This happens when a molten magma in the interior is propelled towards the surface through the fissure of a geological fault. "If that magma reaches a shallow level, it's likely to erupt," Makario continued. However, it is also likely that it will not happen and the magma will stay there.

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