Colombia's Nevado del Ruiz
When Nevado del Ruiz blew in 1985, it , killing 25,000 people. Now the notorious 17,457-foot stratovolcano, situated about 90 miles west of the capital Bogotá in Los Nevados National Natural Park—is again showing signs of unrest.
Recently Nevado del Ruiz has been emitting rising levels of gas and sulfur along with a series of volcanic tremors, likely related to deep magma movements. The ominous signs, understandably, have residents on edge. Local officials have raised the volcano alert level in nearby towns and have fire departments ready for an imminent eruption.
Nevado del Ruiz typically generates plinian eruptions, which produce speedy pyroclastic flows and high-rising columns of gas and volcanic ash that look as though they're ascending to the heavens. This type of explosion is marked by violent ejections of volcanic rock, continuous and powerful blasts of gas, and mud and debris flows called lahars that can wipe out entire towns.