These structures are among the few not carried away or completely destroyed by a lahar that swept through Armero, Colombia, on November 13, 1985. More than 23,000 people were killed by the lahar. Located at the mouth of the Rio Lagunillas (top of image) 74 km from Nevado del Ruiz, Armero's residents should have had plenty of time to leave the city for higher ground just a few hundred meters away.

This tragedy dramatized the need for scientists and emergency-management officials to develop effective procedures for communicating emergency information to people in potentially hazardous areas before a volcano erupts and to inform people in such areas of the activity that could affect them. It also spurred a U.S. Geological Survey scientist to develop a lahar-detection system that today is used to monitor lahars around the world.

More Information

• Deadly lahars from Nevado del Ruiz, Colombia, on November 13, 1985
• USGS lahar-detection system
• Pilot Project: Mount Rainier lahar-warning system