These structures are among the few not carried away or completely destroyed by the lahar that swept through Armero, Colombia. 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. The lahar arrived in Armero about 2.5 hours after the start of the explosive eruption that rapidly melted some of the volcano's ice and snow.
This tragedy dramatized the need for scientists and emergency-management officials to (1) develop effective procedures for communicating emergency information to people in potentially hazardous areas before a volcano erupts; and (2) 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.
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