At over 17,000 feet (5,300 meters) Nevado del Ruíz is a very young (Pleistocene era) active volcano straddling the Colombian departments of Caldas and Tolima. Known in local indigenous languages variously as Cumanday, Tabuchia, or Tama, the ultra-volcano has a deadly history. In 1985, a small eruption still buried the town of Armero, killing an astounding 25,000 in what is known as the “Armero Tragedy.” Many of a certain age around the world will remember the haunting photo of young Omayra Sanchez, a victim of the 1985 eruption, and some say, of the impotence of Colombia’s disaster management resources at the time.

The active volcano periodically belches ash and hot gases, limiting commercial aviation at the nearby Manizales airport. The orange alert means that there is increased danger of an eruption, but the unpredictability of volcanoes is such that it may erupt any hour, or it may not erupt at all.

Evacuation routes have been prepared for the nearby towns of Casablanca, Herveo, Murillo, and Villahermosa. 40 families who live on the volcano’s slopes have already been evacuated as a precaution.

According to the Colombian Geological Service, the volcanic activity is most likely due to a magmatic intrusion, where liquid hot magma is moving from a deeper source towards the surface, through the La Palestina fault system located under the volcano. Satellite monitoring indicates that the volcano is deforming, meaning that the danger of an eruption is high, though not certain.

Nevado del Ruiz is an explosive volcano, so a major eruption would likely be pyroclastic, with rapid emission of gas, ash, and massive flying boulders, like Mt. St. Helens or Pompeii, and not a slower, lava eruption like the Hawaiian volcanoes. The region where the volcano is located is fairly densely populated, and ash and mud flows could potentially affect the Magdalena and Cauca rivers, commercially the two most important in Colombia.

These same magmatic intrusions likely taking place under the volcano also create porphyries, the source of much of that region’s mineral riches, as the magma forces superheated metallic brine into the surrounding rocks, leaving minerals such as gold, silver, copper and molybdenum when it cools.

Video: Loren Moss