The Nevado del Ruiz volcano killed 25,000 people in 1985. Not it has scientists worried again

Experts say the volcano is showing signs of increased activity, which haven’t been observed since the tragedy in the 1980s. As a result, the alert level has been raised from yellow to orange, the second-highest level on the scale and residents on the upper slopes of the volcano are being evacuated.

Last week, the volcano registered an unprecedented average of 6,000 earthquakes per day, likely caused by magma moving through the main fault system, says Colombia’s Geological Service (CGS). Prior to the change in status, the average was 50 per day.

On peak days, the CGS says, there have been as many as 12,000 earthquakes in a single day, though it notes “the number of daily earthquakes alone is not the only indicator that measures the behavior of a volcano.”

On Sunday, the CGS noted a marked decrease in the number of tremors.

Some 57,000 people live in the shadow of Nevado del Ruiz.

An orange alert does not mean an eruption is certain. There have, in fact, been 18 orange alerts since 1985—and no major eruptions in that time. CGS officials say “scientifically it is not possible to know exactly what will happen to the Nevado del Ruiz volcano.”

Still, they said, the activity level “will remain at the orange level for several weeks. During this time, in the event of an acceleration of processes suggesting an imminent eruption or the eruption itself occurring, the activity level will be changed to red level.”

Just as an eruption is impossible to predict, the force of any possible eruption can’t accurately be forecast, scientists say. If the eruption was a larger one, though, the main problems would be ash and mud slides, which was the issue that impacted Armero (as well as the 1980 Mount St. Helens eruption in Washington).